TRANSGENIC PLANTS FOR THE CONTROL OF ANIMAL PARASITES

Abstract: The invention relates to a method of combatting an animal parasite in a host animal which comprises delivering an anti-parasitic protein to the parasite or to a locus thereof by administering the protein to the host animal as a medicament or as a food. The anti-parasitic protein may be an inhibitor of an enzyme of the parasite, for example an inhibitor of a digestive enzyme such as a cysteine protease inhibitor. The parasite may be a helminth or a protozoan for example a nematode. According to one embodiment the anti-parasitic protein is expressed in a transgenic plant which may be a dietary crop for the host animal.

Description: TRANSGENIC PLANTS FOR THE CONTROL OF ANIMAL PARASITES This invention relates to the control of parasites. More particularly the invention relates to the prophylactic and curative control of animal parasites, such as parasitic nematodes, other helminths, protozoa and all parasites possessing proteases. Parasites are organisms which are physiologically dependent on one or more host(s) in a relationship which is generally obligatory and where the organism lives at the expense of its host(s). If bacteria, viruses, fungi and rickettsias are excluded, parasites which infect animals (including humans) can be divided into three principal groups: protozoa, helminths (both of which are endoparasitic) and arthropods which are both endo and ectoparasitic. Parasites infect all species of domestic and wild animals as well as humans. Humans are host to over one hundred species of parasite. Protozoa are unicellular, although they may contain more than one nucleus, and are covered in a plasma membrane as found in other cells. There are at least 45,000 species of protozoa although not all of these are parasitic. Parasitic protozoa include Plasmodium (the causative agent of the disease malaria in humans) which is blood and liver dwelling and transmitted by mosquitoes. At least 300 million people suffer from malaria in tropical and sub-tropical regions. Babesia spp are transmitted by ticks and live in the blood of vertebrates; serious disease is caused in domestic animals, particularly ruminants. Theileria spp. are found in the lymphoid tissue and blood of ruminants and cause diseases including East Coast Fever in cattle. Trypanoso a spp, which cause sleeping sickness in humans and domestic animals, particularly in Africa, mostly live in the blood and tissue fluids of the host and are transmitted by the bite of the tsetse flies. One exception is T cruzi which causes Chagas disease in South and Central America where it infects up to 20 million people. This is transmitted by triatomid bugs. Leislmania tropica and L major, spread by sandflies, cause a disfiguring disease, cutaneous leishmaniasis, in humans, while L donavani causes kala azar which may be both disfiguring and life threatening. It is thought that 100 million people suffer acute or chronic effects of amoebic dysentry and the disease may be responsible for the death of up to 100,000 people per year; amoebic dysentry is due to Entamoeba histolytica an intestinal protozoan parasite. The species is cosmopolitan but in many parts of the tropics and subtropics the prevalence is more than 50% and dysentry is common. Coccidia cause coccidiosis, a common and serious disease of domestic animals; Eimeria tenella which is found in the intestinal cecae of chickens is the best known example, but there are thought to be several important species of coccidia and they occur in other fowl as well as ruminants. Crowded conditions found in batteries can lead to massive infection, which may be severe or fatal. Such is the importance of this group that domestic chickens are maintained on a diet which includes prophylactic drugs (coccidios ats) . The US Department of Agriculture estimates that in 1986 $80 million was lost to US farmers in added labour costs and medicated feeds to control coccidiosis. Another coccidian, Toxoplasma, is an intracellular parasite of many tissues particularly in humans and sheep; stillbirths, spontaneous abortions or disability in the new born may result from infection of the foetus. Toxoplasmosis is responsible for one third of all sheep abortions and causes congenital abnormalities in children at the rate of 1 in 2,000 births in the U.K. Toxoplasmosis has been implicated as a cause of death in immunodeficient patients. Giardia intestinalis which lives in the small intestine of humans and Hexami ta eleagridis in fowl cause highly contagious, diarrhoeal diseases. Infection depends on ingestion of infected water. Giardiasis outbreaks occur frequently in the USA. Trichomonas spp cause a number of disorders of the genito-urinary and digestive system of humans and domestic animals. Helminth parasites are worms; the group includes the flatworms, such as tapeworms and flukes and the roundworms or nematodes. Again, not all flatworms and nematodes are parasites and of those nematodes which are parasitic, many infect plants and have a major economic effect on many crops. The nematodes vary is size from the microscopic filarial worms to the guinea worms (Dracuncul us medinensis) which can be up to 80 cm long. Ascaris lumbricoides is estimated to infect one quarter to one third of the human population of the world; it is found predominantly in the tropics and sub-tropics. Ascaris suum is a related parasite of pigs and has a wide distribution. These are large worms, 15-50 cm long; as with many parasites their success largely depends on high fecundity and poor levels of sanitation. Eggs are readily dispersed around livestock farms and human communities. They are common in the third world as contaminants of drinking water and fresh produce that has been fertilised with faeces or sewage sludge. Immature Ascaris undergo a migration from the intestine through the liver and lungs before growing to adults in the intestine. There may be pathological consequences of the migratory phase: milk spot causes condemnation of pork livers; juveniles in the lungs may give rise to Loeffler's pneumonia. The most significant pathological consequences are due to the adult nematodes in the intestine. Adult Ascaris consume the contents of the intestine reducing protein, fat and vitamin A uptake and induce an intolerance to milk; in moderate and heavy infections this leads to malnutrition and underdevelopment in children and reduced growth rates in pigs. Other symptoms such as asthma and abdominal pain may arise through allergic responses to Ascaris metabolites. Massive infection can lead to fatal blockage of the intestine and wandering adult worms may block pancreatic or bile ducts. The increase in free range pigs in the United Kingdom in recent years favours a resurgence of Ascariasis in pigs. Ascaridia galli is a related species and is a cosmopolitan parasite of chickens. Toxocara canis in dogs and T cati , are broadly similar, though their eggs can hatch if ingested by humans and may give rise to visceral larva migrans. Other nematode parasites of the digestive system include the hookworms such as Ancylostoma and Necator in humans and Bunostomum in ruminants. They attach to the mucosal wall of the intestine and feed on blood and tissue fluids. Infection is through penetration of the skin by juveniles. Trichuris spp. are cosmopolitan though most common in the tropics; they disrupt the caecal mucosa; it is estimated that 700 million humans are infected. Strongyloides spp. are found in the intestinal mucosa of humans and domestic animals. Heterakis gallinarum is a cosmopolitan parasite of chickens and other fowl; they live in the caecum and feed on its contents. The Trychostrongyle nematodes are economically very important parasites of the digestive tract of domestic animals, particularly sheep and cattle: Haemonchus contortus, a blood feeder found in the abomasum, causes an acute anaemia in sheep and cattle; Ostertagia spp., which are similarly located, costs the US cattle industry $600 million each year. The principal effects of the latter are due to the migration of juveniles within the gastric glands, resulting in incomplete digestion, fat depletion and malnurition. Trychostrongylus spp. parasitize the small intestine of many animals including humans causing damage to the mucosa due to burrowing juveniles and feeding adults. Filarial nematodes are blood or tissue-dwelling. The group includes Onchocerca spp. the causative agent of river blindness, which is particularly prevalent in West Africa, and related diseases in domestic animals. Nuchereria bancrofti and Brugia spp. cause filariasis in humans across a broad equatorial belt; elephantiasis is one form of the disease. Trichinella spp. are also tissue dwelling, being found in muscle, particularly of pigs; human infection may occur through eating inadequately cooked pork. The most important flatworms belong to the genus Schistoso a ; this includes species which are parasitic in humans and domestic animals. At least 200 million people suffer from schistosomiasis (Bilharzia) in the tropics and sub- ropics. Infection occurs through direct penetration of the skin by the water-dwelling infective stage; thereafter the parasites (which achieve 1-3 cm in length) are blood-dwelling either in the veins around the bladder or the intestine, depending on the species involved. Other economically important flatworms include Fasciola hepatica, the liver fluke, a cosmopolitan parasite of the bile ducts of sheep and cattle, and Dicrocoelium dendri ticu which inhabits the bile ducts of cattle, sheep, goats and pigs. The latter is common throughout most of Europe and North America. Cestodes, or tapeworms, possess no gut and the body wall or tegument is reponsible for digestion and absorption of external nutrients. In several cases, such as Taenia soli u in humans and pigs and Echinococcus granulosus in sheep the principal pathology is due to the larvae in the body tissues of the host. Adult tapeworms which induce a significant pathology include Diphyllobothrium latum in humans, where pernicious anaemia may result from infection; this is most common in Baltic countries and is due to eating undercooked fish. At present, control of parasitic diseases depends largely on the use of drugs, the control of intermediate hosts and improvements in living conditions, particularly sanitation. Drug treatment is generally expensive, and may need to be repeated frequently whether the aim is prophylaxis or cure. In the third world there are often logistical problems about availabilty of diagnostic expertise and appropriate medication and with some drugs medical monitoring is necessary. Details of the life cycle and pathogenicity of parasites are given in standard texts (see, for example, Schmidt, G M and Roberts, S (1989) Foundations of Parasitology, Times Mirror/Mosby College Publishing, St Louis, U.S.A.; Urquhart, G M et al (1987) Veterinary Parasitology, Longman Scientific and Technical, London, U.K.) . Proteases are normally divided into four main classes of serine, cysteine (thiol) , aspartyl (carboxyl) and metallo-proteases (Barrett, 1980) . Proteases are involved in important physiological processes that range from protein catabolism or post-translational modification as found in lysosomal metabolism (Kirschke, et al 1980) , to involvement in extracellular digestion of dietary proteins. There has been much interest in the characterisation, cloning and description of the functional significance of proteases in a range of parasites including nematodes, other helminths such as Schistosoma mansoni (Chavez-Olortegui et al 1992; Landsperger et al 1982), and protozoans, including Entamoeba histolytica (Luaces & Barrett, 1988) , Plasmodi um falciparum (Rosenthal & Nelson, 1992) , Trypanosoma spp (Eakin et al 1992; Mbawa et al 1992) and Theileria annulata (Baylis et al 1992) . ϊ' .rm3.Mϋ/00419 Parasite proteases have been studied recently for their roles in infection and nutrition and to explore the potential they offer as targets for vaccine development (McKerrow, 1989) . For instance, proteases of all four classes have been reported from animal parasitic nematodes (Sakanari, 1990) . The infective larvae of Dirofilaria i mi tis show metallo-protease activity in their secretory/excretory products (Richer et al , 1992) . Nippostrongylus brasiliensis also possesses this class of proteins in both infective and adult stages. Cysteine proteases occur in adults of N. brasiliensis (Healer et al 1991) and two proteases of this class have been cloned for Haemonchus contortus (Cox et al , 1990, Pratt et al , 1990) . Expression of the proteases of H. contortus are developmentally regulated and the protein is present at much higher levels in feeding adults than in the non-feeding, infective larvae (Pratt et al , 1990) . In addition, the free-living species Caenorhabdi tis elegans has also been studied and shown to possess both aspartic and cysteine protease activity (Sarkis et al , 1988) . Generic oligonucleotide probes were designed for conserved regions of proteases and used to PCR-amplify gene fragments from C. elegans and certain parasitic protozoa (Sakanari et al , 1989) . The approach led to characterisation of a cysteine protease gene from C. elegans . In si tu hybridisation has established expression of this gene within the intestinal cells of this animal which strongly suggests a role for this enzyme in digestion (Ray & McKerrow, 1992) . Ascaris has been shown to possess cysteine (Maki and Yanagisawa, 1986) proteases as digestive enzymes in contrast to other classes of proteases used by mammals in protein digestion (Barrett, 1980) . Ascaris secretes inhibitors of proteases other than cysteine proteases into the intestinal lumen so lessening nutritional competition from its host (Martzen et al , 1990, Bennett et al , 1992) . Animals are unable to synthesise all the amino acids which they require and so proteins are essential to their nutrition. Proteases are used by animals to break down proteins into smaller molecules (peptides) as part of the assimilation of food. In addition, they are of value to many parasites in assisting the invasion of hosts. The substrate specificity of proteases from different sources vary and do not provide a basis on which to define them. The enzymes act through four distinct catalytic mechanisms and this allows division into four classes of serine, cysteine, aspartic and metalloproteases. Serine proteases are widespread and diverse and cysteine proteases are also widely distributed and occur in bacteria, microorganisms, plants and animals. The metalloproteases are also widely distributed and occur in bacteria, eukaryotic microorganisms, plants and animals. The aspartic class has a more limited distribution and seems restricted to eukaryotes. A wide range of inhibitors are known but of particular interest are various proteins that are not substrates but inhibitors of such enzymes. These protease inhibitors occur widely, for instance there is a protease inhibitor of cysteine proteases (i.e. a cystatin) in chick egg white and several human and rat cystatins. Many protease inhibitors occur in plants and in particular they accumulate in seeds. The currently recognized plant protease inhibitor (PI) families are Bowman-Birk, Kunitz, potato 1, potato 2, cucurbit, the cereal superfamily, Ragi 1-2, maize 22kDa and the cystatin family. The cystatin family includes oryzacystatin I and II which occur in rice and a cystatin from maize which is termed zeacystatin herein. Oryzacystatin I has been expressed transgenically in tobacco plants (Masoud et al , 1993) establishing the ability of cystatins to be expressed as transgenes. The natural role of Pis in plants include anti-pathogen or anti-herbivore effects. For instance Cowpea trypsin inhibitor (CPTi) is a double headed serine protease inhibitor for which protein and cDNA sequence is known (EP-A-0 272 144; Hilder et al 1989) . There are reports that variation in CPTi levels in seeds can be correlated with field resistance to bruchid beetles suggesting that CPTi protects seeds of Cowpea from herbivory by certain insects. A cassette including a CaMV35S promoter and the coding sequence for a mature CPTi inhibitor has been inserted into tobacco using Agrobacteri um tumefaciens-mediated transformation. There was a correlation between the level of expression of CPTi and both survival of Heliothis virescens and the level of damage caused by these insect larvae to the plants (Hilder et al , 1987; EP-A-0 272 144) . Protease inhibitors such as CPTi have been shown to have protective effects against plant parasitic nematodes such as Globodera and Meloidogyne species. Expression of CPTi in plants suppresses the growth rate, fecundity and sex ratio of these crop pests (EP-A-0 502 730) . EP-A-0 348 348 relates to the production of transgenic plants expressing protease inhibitors to render the plant resistent to pests such as insects, mites, fungi and bacteria (although there is no reference to plant nematodes) . Examples include transgenic maize, potatoes, tomatoes, orchard grass, cotton and tobacco expressing serine protease inhibitors and the cysteine protease inhibitor chicken egg white cystatin. WO 92/21753 relates to the use of so-called midgut effective plant cystatins to control insect pests which attack plants. The specification discloses transgenic plants expressing these cystatins and examples are transgenic maize, rice, cotton, alfalfa, dry bean, potato and rape seed which express potato papain inhibitor. The use of proteases such as papain in the treatment of intestinal helminth infections including Ascaris has been documented (Pawlowski, 1990) and is derived from the traditional use of leaves and latex of the papaya plant as a vermifuge (McKee, 1962) . However, this traditional use of proteases as a vermifuge, which was first reported nearly 200 years ago, is not now regarded as an effective treatment and does not suggest the use of proteins with a specific anti-parasite activity in combating animal parasites. Pharmaceutical uses for cystatins unrelated to the control of pests have been proposed. EP-A-0373 771 relates to the use of cystatins in the treatment of allergic and bone diseases. WO 88/09384 proposes the use of cystatin C as an anti-viral, anti-bacterial and anti-cancer agent and in the treatment of sciatica and brain haemorrhage. WO 94/15578 relates to oral and edible compositions comprising cystatin S, cystatin SA or cystatin SN where the cystatin is said to have an anti-caries effect. JP-040178335 relates to the use of protease inhibitors including cystatins in the treatment of viral diarrhoea in children and domestic animals . There is clearly still a need for better control of animal parasites. It is an object of the present invention to provide an improved prophylactic and curative approach for parasites in humans and livestock and, in particular, a method which is not dependent on periodic dosing as either a prophylactic or curative measure. It has now surprisingly been found that prophylactic and curative control of animal parasites can be achieved by administration of an anti-parasitic protein, preferably an inhibitor of an enzyme of the parasite, to the potential host, for example as a medicament or as part of the food of the host. As used herein, references to "combating" an animal parasite are intended to include both prophylactic and curative control of the parasite. It should be understood that as used herein the terms "animal", "mammal" and the like are used in their normal biological sense as including man. According to one aspect, the present invention provides a method for combating an animal parasite in a host animal which comprises delivering an anti-parasitic protein, preferably an inhibitor of an enzyme of the parasite, to the parasite or to a locus thereof by administering the protein to the host animal as a medicament or as a food. According to one preferred embodiment of the invention, the anti-parasitic protein is administered orally to the host animal either as part of the food of the animal or as a medicament. However, other suitable modes of administration can be used provided that they result in an effective amount of the anti-parasitic protein being delivered to the locus of the parasite. For example oral administration may be appropriate in the case of a parasite which lives in the intestine of the host animal and consumes the host's food such as Ascaris and Ascaridia . Oral administration may also be appropriate in the case of intestinal parasites which feed on blood or tissue fluids of the host, such as Giardia , Haemonchus and hookworm. Parasites in the intestinal tissues, for example Coccidia and Ostertagia may also be susceptible to an anti-parasitic protein administered by the oral route. Non-intestinal parasites, such as blood and tissue dwelling parasites, may also be susceptible to anti-parasitic protein administered orally provided that an effective amount of the protein can be absorbed into the bloodstream. Alternatively, anti- parasitic protein can be incorporated into a medicament for parenteral administration, for example for use as an injection, or for topical administration. Parasites in skin such as Leishmania and Onchocerca may be particularly susceptible to topical administration of the anti-parasitic protein . The following is a summary of possible modes of administration of the anti-parasitic protein together with examples of target parasites against which particular modes of administration may be effective: Administration of an anti-parasite protein to the host animal or its locus as a medicament or as a food or incorporated into food i.e. by oral administration Members of the Order Ascaridata including Ascaris suum, Ascaris l umbricoides, Ascaridia galli , Anisakis spp, Parascaris equorum, Toxocara canis, T cati , T vi tulorum and Toxascaris leonina . Trichostrongyles including Nematodirus battus , Nematodirus spathiger, Nematodirus filicollis , Haemonchus contortus, Trichostrongylus colubriformis, T tenuis, T capri cola , T falcatus, T rugatus, T axei , Ostertagia ostertagi , 0 circumcincta , 0 trifurcata, Oesophagostomum radiatum and Cooperia cuticei . Strongyloids including Strongyloides stercoralis , S ransomi and S papillosus . Hookworms including Necator a ericanis, Ancylostoma duodenale, . ceylanicum, A braziliense, A caninum and Bunostomum spp. Members of the Order Trichurata including Trichuris trichuria, T suis, T ovis, Capillaria hepatica , C annulata , C caudinflata . Oxyurids including Heterakis gallinaru , Oxyuris egui , Enterobius vermicularis and E gregorii . Tapeworms including Taenia solium, T saginata, Diphyllobothrium latum, Echinococcus granulosus, E hydatigena, Hymenolepis diminuta and H nana . Trematodes including Fasciola hepatica, F gigantea, Fasciolopsis buski , Dicrocoelium dendri ti cum, Chlonorchis sinensis and Opisthorchis felineus . Coccidia including Eimeria acervulina, E necatrix, E maxima, E brunetti, E tenella, E meleagrimitis, E danailova, E anseris, E alabamensis, E bovis, E zuernii, E ahsata, E arloingi, E debliecki, Isospora belli, Toxoplas a gondii, Sarcocystis hirsuta, S porcifelis, S cruzi, S tenella, S jberϋrami, S fayeri, S meischeriana, S suihominis, S hominis, S gigantea, Besnoita bennetti, B wallacei, Hammondia heydorni and Cryptosporidium spp. Intestinal flagellates including Giardia intestinalis, Hexamita meleagridis, Histomonas meleagridis, Trichomonas gallinarum, Spironucleus meleagridis and Dientamoeba frag His . Amoebae including Enta oeba histolytica, E hartmanni, E gingivalis, E coli, Endolimax nana, Naegleria fowler i and lo a-πoeJa buetschlii. Administration of an anti-parasite protein to the host animal or its locus as a medicament by injection into the bloodstream or tissues Members of the family Sarcocystidae including Toxoplasma gondii, Sarcocystis hirsuta, S porcifelis, S cruzi, S tenella, S bertrami, S fayeri, S meischeriana, S suihominis, S hominis, S gigantea, Besnoita bennetti, B wallacei and Hammondia heydorni. Other protozoa including Trypanosoma brucei, T brucei jrucei, T brucei gambiense, T brucei rhodesiense, T congolense, T vivax, T cruzi, T equiperdum, T equinum, T evansi, T r angel i, T theileri, Leishmania tropica, L tropica tropica, L tropica major, L aethiopica, L donavani, L donavani donavani, L donavani archibaldi, L donavani infantum, L donavani chagasi, L mexicana, L mexicana mexicana, L mexicana amazonensis, L mexicana pifanoi, L mexicana aristedesi, L mexicana garnhami, L braziliensis, L braziliensis braziliensis, L braziliensis guyanensis, L braziliensis panamensis, L peruviana, L enriettii, L hertigi, L hertigi hertigi, L hertigi deanei, L aethiopica, Trichomonas vaginalis, T tenax, T foetus, Pentatrichomonas hominis, Plasmodium vivax, P falciparum, P ovale, P malariae, P gallinaceum, Babesia bigemina, B bovis, B berbera, B divergens, B argentina, B major, B caballi, B equi, B ovis, B motasi, B traumanni, B canis, B gibsoni, B felis, Theileria parva, T annulata, T mutans, T hirei, T sergenti, T hirci, T ovis and Hae atoxenus veliferous. Filarial nematodes including PΛicΛereria jbancrofti, Brugia alayi, Onchocerca vovulus, 0 gutterosa, 0 gibsoni, Loa loa, Dipetalonema perstans, D streptocerca, Mansonella ozzardi and Dirofilaria imitis . Members of the Order Trichurata including Trichinella spiralis and T psuedospiralis. Trematodes including Schistosoma mansoni, S haematobium, S japonicum, S mekongi, S matthei, S intercalatum, S bovis, Fasciola hepatica, F gigantea, Fasciolopsis buski , Dicrocoelium dendriticum, Chlonorchis sinensis and Opisthorchis felineus . Metastrongyles including Dictyocaulus viviparis, D filaria, D arnfieldi and Angiostrongylus cantonensis . Tapeworms including Taenia solium, T saginata, Diphyllobothrium latum, Echinococcus granulosus, E hydatigena, Hymenolepis diminuta and H nana. Members of the Order Ascaridata including Toxocara canis, T cati, T vitulorum and Toxascaris leonina. Guinea worms including Dracunculus medinensis . Administration of an anti-parasite protein to the host animal or its locus as an ointment or cream for topical application Filarial nematodes including Onchocerca vovulus, 0 gutterosa, O gibsoni, Loa loa, Dipetalonema streptocerca, Mansonella ozzardi. Leishmania species including Leishmania tropica, L tropica tropica, L tropica major, L aethiopica, L donavani, L donavani donavani, L donavani archibaldi, L donavani infanturn, L donavani chagasi, L mexicana, L mexicana mexicana, L mexicana amazonensis, L mexicana pifanoi, L mexicana aristedesi, L mexicana garnhami, L braziliensis, L braziliensis braziliensis, L braziliensis guyanensis, L braziliensis panamensis , L peruviana, L enriettii , L hertigi , L hertigi hertigi, L hertigi deanei , L aethiopica . Guinea worms including Dracunculus medinensis . Administration of an anti-parasite protein to the host animal or its locus as a pessary Trichomonas vaginal is . For example, the anti-parasitic protein may be an inhibitor of a digestive enzyme of the parasite, such as a cysteine protease inhibitor. The animal parasite may be a helminth, for example a nematode, or a protozoan. Preferably the anti-parasitic protein is an inhibitor of a class of protease found in the parasite but not at the locus of the parasite in the host. As noted above, it has already been proposed that protease inhibitors such as CPTi have protective effects against insects (EP-A-0 272 144, EP-A-0 348 348 and WO 92/21753) and plant parasitic nematodes such as Globodera and Meloidogyne species (EP-A-0 502 730) . However, there are such large differences between the physiology, mode of nutrition and environment of both herbivorous insects and plant pathogens, and that of any animal parasites that it could not have been predicted that a protease inhibitor effective against any insect species or plant pathogen would show efficacy against any animal parasite. In addition any protective role of a plant protease inhibitor against either a herbivore or a pathogen can have no such benefit for the plant against animal parasites with which it does not interact. The plant parasitic nematodes used in previous work (EP-A-0 502 730) modify plant cells to form specialised feeding sites and their nutrition is very different from that shown by most animal parasitic nematodes. It was therefore quite unpredictable that a particular protease inhibitor, even one that influences a pathogen or herbivore including plant parasitic nematodes feeding in roots, would also influence animal parasites including nematodes when the plant is ingested by livestock or humans. As used herein the term "anti-parasitic protein" means a protein which has a specific anti-parasitic action by a mechanism not involving the host immune system. Some activity against the host may not be precluded in some cases but the action against the parasite must be sufficiently specific for the protein to be useful in combating the parasite. Proteins which cause non-specific damage to host and parasite alike are excluded. The anti-parasitic protein used according to the present invention is preferably an inhibitor of a digestive enzyme of the parasite, for example an inhibitor of plant or animal origin. The protease inhibitor may be a cysteine protease inhibitor, such as a cysteine protease inhibitor from maize. Other suitable plant cysteine protease inhibitors include those from rice, papaya, potato, Wisteria, soybean, pineapple, broom or other legumes or other plant species. Alternatively, the protease inhibitor is or has significant structural and functional similarity to a cysteine protease inhibitor from animal or other sources such as chicken egg white cystatin, human cystatin A, human cystatin B, human cystatin C, human cystatin S, rat cystatin , rat cystatin β, kininogen, L-kininogen and H-kininogen. Protease inhibitors such as the cystatins from maize and rice occur in seeds of these plants and not in the roots of these plants where nematodes such as Meloidogyne occur. Therefore it is surprising that these stored seed proteins are effective against animal parasites even after their oral uptake by the host. The protease inhibitor must survive passage to the locus of the parasite and be taken up in levels that show an effect against the parasites. This is very different from demonstrating an effect against a plant parasitic nematode for a protease inhibitor expressed by its host i.e. a plant. As already indicated, the protease inhibitor is preferably effective against a class of proteases found in the parasite but not at the locus of the parasite in the host, for example an inhibitor of a class of proteases found in intestinal nematodes but not in the vertebrate intestine. The cystatins fall within this class but whilst there are no proteases in the mammalian intestine likely to be inhibited by cystatins, there are cysteine proteases elsewhere in the mammalian body so that care will be needed that intravenous administration of cystatins does not produce an unacceptable toxicological hazard. Administration of other classes of protease inhibitors may be less hazardous and thus more appropriate for tissue dwelling parasites. The anti-parasitic protein used according to the present invention may also be an antibody acting on the parasite without involvement of the host immune system either in the production of the antibody or its action against the parasite. For example, the antibody could bind to and thereby block the active site of an enzyme of the parasite. The enzyme can be a digestive enzyme (protease) of the parasite, in which case the antibody can also be regarded as a protease inhibitor, or can be an enzyme with another function vital to the parasite. Such antibodies will generally be monoclonal antibodies and can be produced by conventional hybridoma technology and can be modified in various ways as desired, for example by removal of a region of the antibody such as the Fc region. The anti-parasitic protein may also be an antibody specific for an antigen expressed by the parasite and which has been modified to conjugate an antibody protein specific for a parasite with a toxin for the parasite. Suitable monoclonal antibodies, optionally conjugated with a toxin, can be produced by conventional methods of recombinant DNA technology. - . Recent work has established the potential of plant biotechnology for medical applications in that antibodies have been expressed in plants (Hiatt et al 1989, During et al 1990) and use of these antibodies for passive immunisation has been suggested (Haitt & Ma, 1992) . The Hepatitis B surface antigen (Mason et al 1992) , the non- toxic β-chain of cholera toxin and antigens from Streptococcus mutans and Escherichia coli have been expressed in plants as a future basis for administering oral vaccines (reported by Moff t, 1993) . This approach is very distinct from the present invention which does not envisage use of proteins that act via the immune system by initiating an immune response as immunogens do within a vaccine. Oral vaccines act in this way after ingestion of the antigen. The anti-parasitic proteins according to the present invention may be antibodies produced by the mammalian immune system or by use of hybridoma technology which may optionally be modified, and which may subsequently be engineered into plants, and which act directly on the parasite without involvement of the host immune system. Such antibodies are less likely to suffer from the problems of degradation in the gut which arise in the development of an oral vaccine or an antibody for the induction of passive immunity. In addition protease inhibitors are also able to withstand passage through the mammalian or avian gut system without loss of activity. According to one embodiment of the invention, the anti- parasitic protein is expressed by a transgenic plant. The means by which transgenic plants expressing heterologous proteins throughout the plant or at various locations or at various stages of their life-cycle are known. In addition, transgenic plants have already been produced expressing protease inhibitors as a means of protecting the plant against plant parasites (see EP-A-0 272 144, EP-A-0 348 348, WO 92/21753 and Masoud et al , 1993) . The same methods can be used to produce transgenic plants expressing anti- parasitic proteins, for example cysteine protease inhibitors of plant or animal origin. Without wishing to be bound by specific methodology, an example of the steps required to produce a transgenic plant expressing an anti-parasitic protein is as follows: isolation of mRNA from a suitable source and preparation of cDNA encoding the anti-parasitic protein using standard techniques of cDNA cloning; - transfer of the cDNA encoding the anti-parasitic protein into an expression cassette including a promoter and other regulatory elements suitable for use in the intended host plant; transfer of the expression cassette into a transgenesis vehicle suitable for infection of the intended host plant, e.g. -AsrroJba terium tumefaciens ; Infection of the intended host plant with the transgenesis vehicle. Many alternatives exist for the steps referred to above and in some cases some of the steps may already have been carried out, for example, cDNA encoding the anti-parasitic protein may already exist. For example, protease inhibitors can be expressed constitutively using a promoter such as CaMV35S but in addition some of the more efficacious inhibitors as described herein can be produced in a manner which enhances efficacy by confining expression to part only of the transgenic plant. For example in the case of a protease inhibitor produced naturally only in the seeds of the plant in which it occurs, the promoters naturally occurring in the gene encoding the protease inhibitor can be used to control expression to just seeds of the transgenic plant. Suitable plants which can be transformed with DNA encoding the anti-parasitic protein include dietary crops for the intended host of the animal parasite, such as fruit crops, vegetables and tubers, oil crops, sugar crops, forage legumes. Fiber plants and woods and drug crops can also be used. Suitable plants which can be transformed with DNA encoding anti-parasitic protein, classified according to the use of the plants, are set out in the following Table A. TABLE Plant Classification According to Use CEREALS Monocot Avena nuda (chinensis) Chinese naked oat A . sativa Common oats Aleusine coracan African millet Eragrostis tef Tef grass Hordeum distichum Two-row barley H. vulgare Barley Oryza sativa Rice Panicum i talicium Italian millet P. miliaceum Broomcorn millet Pennisetum glaucum Spiked millet P. spica turn (americanum) Pearl millet Secale cereal e Rye Sorghum vulgare Grain sorghums Tri ti cala hexaploide Triticale Tri ticum aestivu Common wheat T. di coccum Emmer T. durum Abyssinian hard wheat T. monococcum Einkorn wheat Zea mays Starch, sweet corn Dicot Amaranthus pani culatus Grain amaranth Fagopyru esculentum Buckwheat F. tatari cum Rye buckwheat LEGUMES Dicot Arachiε hypogea Peanut, groundnut Cajanuε indicuε Pigeon pea Cicer arietinum Chickpea Dolichoε lablab Hyacinth bean Glycine gracilas Manchurian soya G. max Soybean G. uεεurienεiε Wild soya Lathyruε εativuε Grass pea Lens culinaris Lentil Mucuna pruriens Cowitch, Florida velvet bean Phaεeoluε acutifoliuε Tepary bean P. aureuε Mung, green gram P. lunatuε Lima bean, Sieva P. coccineus (mul tiflorus) Scarlet runner bean P. mungo Mung bean, black gram P. vulgar iε French, common, kidney or dwarf bean Piεum εativum Pea Vicia faba Broad bean, horse bean, field bean Vigna angular iε Adzuki bean V. radiata Mung bean V. seεquipedaliε Asparagus bean, yard-long bean V. εinenεiε Cowpea FRUIT CROPS Dicots Amygdaluε communiε Almond Ananas comosus Pineapple Artocarpuε communiε Breadfruit Carica papaya Papaya Ci trulluε vulgar iε Watermelon Ci rus grandiε Pummelo C. medica Lemon, citron C. nobiliε Tangerine C. reticulata Mandarin C. sinensis Orange Cydonia oblon a Quince Diospyroε kaki Japanese persimmon Ficuε carica Fig Fragaria chiloensis Wild strawberry F. virginiana Strawberry Litchi chinenεiε Lychee Maluε aεiatica Chinese apple M. pumila Apple Mangifera indica Mango Moruε rubra Red mulberry Muεa cavendiεhii Banana M. paradiεiaca Banana Paεεiflora eduliε Passion fruit, purple granadilla Persea americana Avocado pear P. ligularis Passion flower Phoenix dactylifera Date palm Prunuε armeniaca Apricot P. aviu Sweet cherry, mazzard P. ceraεifera (divaricata) Cherry plum P. ceraεuε Cherry P. domestica European plum or prune P. maheleb Maheleb cherry P. perεica Peach and nectarine P. pεeudoceraεuε Cherry P. εalicinia Japanese peach P. εerotina Wild black cherry Pεidiu guajava Guava Punica granatum Pomegranate Pyruε communiε Pear P. uεεurienεis Chinese pear Ribeε groεεularia Gooseberry R. nigrum Blackcurrant R. rubrum Red currant, white currant Rubuε idaeuε European raspberry R. εtrigoεuε American raspberry Tamarinduε indica Tamarind Vaccinium anguεti folium Sugarberry V. aεhei Rabbiteye blueberry V. corymboεum Highbush blueberry V. myrtilluε Canada blueberry V. oxycoccoε Cranberry Viburnum tr ilobum American cranberry Vitiε labruεca Fox grape V. vinifera Grape VEGETABLES AND TUBERS Monocot Alii urn aεcalonicum Shallot, green onion A . cepa Onion A. chinenεe Onion A. fiεtuloεum Welsh onion A . porrum Leek A. εativum Garlic A. εchoenoprasum Chives Asparagus officinaliε Asparagus (var. attilis) Zea mays Sweet corn Dicot Amoracia lapathifolia Horseradish Apium graved ens Celery Arabidopεiε thai i ana Common wall cress, thale cress Beta vulgaris Sugar, mangold or garden beet Brasεica alboglabra Chinese kale B . campe tri ε Turnip rape B. carinata Abyssinian mustard B. cernua Karashina B . chinenεiε Chinese mustard or pak-choi B . hirta White mustard B. juncea Brown mustard, pai B . kaber Charlock B. napobraεεica (rutabaga) Swede B . napuε Rape, oilseed rape, kale B . nigra Black mustard B . oleracea Cole, kale, collards, brussel sprouts, cauliflower, cabbage, kohlrabi, broccoli B . pekinenεiε Chinese cabbage or celery cabbage B . rapa Turnip Cajanuε cajan (indicuε) Pigeon pea Canavalia enεiformiε Jack bean Canna eduliε Edible canna Capiεcum annuum Common cultivated pepper C. chinenεe Pepper C. fruteεcenε Cayenne pepper C. pendulum Pepper C. pubescens Pepper Cichorium endivia Endive C. intybuε Chicory Colocaεia antiquorum Taro Cra be mariti a Sea kale Cucumiε melo Melon, cantaloupe C. εativuε Cucumber Cucurbi ta ficifolia Malabar gourd C. foetidiεsima Calabazilla, buffalo gourd C. maxima Pumpkin C. moεchata Winter pumpkin C . pepo Summer squash, vegetable marrow Cynara εcolymuε Globe artichoke Daucuε carota . Carrot Dioεcorea εlata Yam D . batataε Chinese yam D. cayenn enεiε Attoto yam Eruca εativa Rocket salad, rocket or roquette Ipomea batataε Sweet potato Lactuca εativa Lettuce Lepidium εativum Garden cress Lycoperεicon ceraεiforme Cherry tomato L. eεculentum Tomato Mahihot utiliεεi a Manioc, cassava Naεturtium officinale Water cress Paεtinaca εativa Parsnip Petroεelinum criεpum Parsley (εativum) Phyεaliε peruviana Ground cherry Piεum εativum Pea Raphanuε εativuε Radish Rheum officinale Rhubarb R . rhapon ti cum English rhubarb Scorzonera hiεpanica Black salsify Sechium edule Chayote Solanum andigenum Andean potato S. elongena Egg plant S. muricatum Pepino S. phureja Potato S. tuberoεum Common potato Spinacia oleracea Spinach NUTS Dicot Anacardium occidentale Cashew Arachiε hypogea Peanut Carya illinoinenεiε Pecan C. ovata Shagbark hickory Caεtanea εativa Chestnut Cocoε nucifera Coconut palm Coryluε americana American hazel, filbert C. avellana European hazel, cobnut Juglanε nigra Black walnut J. regia English walnut J. εinenεiε Walnut Li tchi chinenεiε Lychee Macadamia integrifolia Queensland nut Piεtacia vera Pistachio nut Prunuε amygdaluε Almond OIL CROPS (COOKING OR VEGETABLE OILS) Monocot Zea mayε Corn Dicot Aleurites cor data Tung, China wood oil A . moluccana (triloba) Candlenut Arachiε hypogea Ground nut , peanut Braεεica campeεtriε Rapeseed oil , canola oil B. napuε Rapeseed oil , canola oil Cannabiε εativa Hempseed oil Carthamuε tinctoriuε Saf flower oil , false saffron Cocoε nucifera Coconut palm Elaeiε guineenεiε Oil palm Gly cine graciluε Manch, soya G. max Soybean G. uεεurienεiε Wild soya Goεεypium hirεutum Cottonseed oil Helianthuε annuε Sunflower Linu uεi tatiεεimum Flax Olea europaea Olive Papaver εomniferum Poppy seed Ri cinuε communiε Castor bean Sesamum indicum Sesame SUGAR CROPS Monocot Saccharum officinarum Sugarcane (offi cinarum x εpontaneum) S. robuεtum Sugarcane S. εinenεe Sugarcane S. εpontaneum Kans grass Sorghum dochna Sorgo syrup, sugar sorghum Dicot Acer εaccharum Sugar maple Beta vulgariε Sugar or mangold beet FORAGE AND TURF GRASSES Monocot Agropyron criεtatum Crested wheatgrass A . deεertorum Crested wheatgrass A . elongatum Tall wheatgrass A . intermedium Intermediate wheatgrass A. εmithii Western wheatgrass A . εpicatum Blue bunch wheatgrass A . tra chycaul rn Slender wheatgrass A . tri chophorum Pubescent wheatgrass Alopecuruε pratenεiε Meadow foxtail Andropogon gerardi Big bluestem Arrhenatherum elatiuε Tall oat grass Bothriochloa barbinodiε Cane bluestem B m iεchaemum King ranch bluestem B . εaccharoideε Silver bluestem Bouteloua curipendula Side oats grama B . eriopoda Black grama B . graciliε Blue grama Bromuε erectuε Upright brome B . inermiε Smooth brome B . ripariuε Meadow brome B . unioloideε Cenchrus ciliariε Buffel grass Chloriε gayana Rhodes grass Cymbopogon nardus Citronella grass Cynodon dactylon Bermuda grass Dactyl is glomerata Cocksfoot, orchard grass Dichanthium annul a turn Kleberg bluestem D. ariεtatum Angleton bluestem D. fecundum D . εeri ceum Silky bluestem Digi taria decu benε Pangola grass D. εmutεii Elymuε anguεtuε Altai wild rye E. junceuε Russian wild rye Eragroεtiε curvula Weeping love grass Feεtuca arundinacea (elation) Tall fescue F. ovina Sheeps fescue F. pratensiε Meadow fescue F . rubra Red fescue Lolium multiflorum (i talicum) Italian ryegrass L. perenne Perennial ryegrass L. rigidum Panicum maximum Guinea grass P. americanum P. purpuraεcenε Para grass P. virgatum Switchgrass Paεpalum dilatatum Dallis grass, large water grass P. notatum Bahia grass Penniεetum clandeεtinum Kikuyu grass P. purpureum Dry napier grass Phalariε arundinacea Reed canary grass Phleum bertolinii Timothy P. pratenεe Timothy Poa fendleriana Mutton grass P. nemoraliε Wood meadow grass P. pratenεiε Kentucky bluegrass, smooth stalked meadow grass P. trivialiε Rough stalked meadow grass Setaria εphacelata Rhodesian timothy S. ancepε Sorghaεtrum nutanε Indian grass Sorghum halepenεe Johnson grass S. εudanenεe Sudan grass S. vulgare Great millet FORAGE LEGUMES Dicot Coronilla varia Crown vetch Crotalaria juncea Sunn hemp Deεmodium intortum D. heterophyllum D. εandwicenεe D. uncinatum Digitaria decumbenε Gly cine wight ii Lespedeza εtipulacea Korean lespedeza L. εtriata Common lespedeza L. εericea Lotononiε baineεii Lotuε corniculatuε Birdsfoot trefoil L . maj or L. uliginoεuε Lupinuε albuε Wolf bean, white lupin L. angustifoliuε Blue lupin L. luteuε European yellow lupin L. mutabiliε South American lupin Macroptiliom atropurpureum Medicago arabica Spotted burr-clover M. arbor ea Tree alfalfa M. falcata Yellow lucerne M. hiεpida Carlifornia burr-clover M. littoraliε M. polymorpha M. εativa Alfalfa M. tribuloideε Barrel medic M. trunculata Melilotuε albuε White sweet clover M. officinaliε Yellow sweet clover Onobrychiε viciifolia Sainfoin Orni thopuε εativuε Serradella Pueraria thunbergiana Kudzu vine Styloεantheε guyanenεiε S. lamata S. limit is Trifolium alexandrinum Egyptian clover T. auguεtifolium Fineleaf clover T. diffuεum Rose clover T. fragiferum T. hybrid m Alsike clover T. incarnatum Cromson clover T. ingreεcenε Ball clover T. pratenεe Red clover T. repenε White clover T. reεupinatum Persian clover T. εubterraneum Subterranean clover Trigonnela foenum-graecum Fenugreek Vicia εativa Common vetch V. villoεa Hairy vetch V. atropurpurea Purple vetch V. anguεtifolia Narrowleaf vetch V. daεycarpa Woolly pod vetch V. ervilia Monantha (bitter) vetch V. pannonica Hungarian vetch V. calcarata Bard vetch FIBER PLANTS AND WOODS Monocot _3a_τιJ usa vulgar iε Bamboo Dicot Agave εiεalena Sisal hemp Boehmeria nivea Rhea fibre, ramie Cannabiε indica Hemp C. εativa Hemp Ceiba pentandra Silk cotton tree, kapok Corchoruε mucronata (εtriata) Hemp Goεεypium arbor um Tree cotton G. barbadenεe Egyptian cotton G. herbaceum Cotton G. hirεutum Upland cotton G. manking Oriental cotton Linum anguεtifolium Wild flax L. uεi tatiεsimum Flax . Λfusa textileε Manila hemp, abaca DRUG CROPS Dicot Angelica archangelica Angelica Chrysanthemum cinerarii folium Palm pyrethrum Camellia sinenεiε Chinese tea C. coccineum Pyrethrum Coffea arabica Coffee C. canephora Quillow coffee Cola acuminata Kola nut Nicotiana ruεtica Tobacco N. tabacum Tobacco Papaver dubium Poppy P. εomniferum Opium poppy Theobroma cacao Cocoa SPICES AND FLAVOURINGS Monocot Vanilla fragranε Vanilla Dicot Artemisa dracunculuε Tarragon Cinnamomum zeylanicum Cinnamon Hibiεcuε eεculentuε Okra Salvia officinaliε Sage Thymuε vulgar iε Thyme Pimpinella aniεu Anise Metha arvenεiε Menthol M. piper i ta Peppermint M. viridiε Spearmint Coriandrum εativum Coriander Most of the crops mentioned in the above table can be used as human foods except for the forage and wood crops. Depending on the nature of the plant, the transgenic plant can be administered directly to the intended host of the animal parasite as food or can be processed to yield a medicament. Where the transgenic plant is administered as a food, the plant will generally already be used as a food or a source of food for the animal in question and the plant can be eaten directly by the animal or processed in the usual way for that plant. In the case of a transgenic plant intended to yield a medicament, the plant can be processed in an appropriate manner, for example, to concentrate or extract the anti-parasitic protein, which may then be formulated into a composition, optionally with appropriate excipients. The following Table B sets out examples of food crops of domestic animals and crops for which animal feed is derived, classified by the type of animal. TABLE B Examples of Food Crops of Domestic Animals and Crops from which Animal Feed is Derived Poultry: alfalfa, artichokes, barley, beans, broomcorn, buckwheat, cabbage, carrots, cassava, clover, coconut, cotton seed, cowpea, field bean, flax seed, hemp seed, kale, lentils, lettuce, linseed, lucerne, lupin, maize, mangold, millet, oat, parsnip, pea, peanut, potato, rape, rice, rutabagas, rye, sorghum, soy bean, sugar beet, sugar cane, sunflower, swede, turnip, velvet bean, wheat. Pig: alfalfa, barley, brussel sprout, buckwheat, cabbage, carrots, cassava, castor bean, coconut, cottonseed, field bean, kale, kapok/ kohlrabi, lentil, lucerne, lupins, maize, mangold, mung bean, mustard, oat, palm kernel, parsnip, peanut, peas, potato, pumpkin, rapeseed, rice, rye, safflower, salseed, sesame, sorghum, soybean, sugar beet, sunflower, sweet potato, triticale, wheat. Cattle: barley, brussel sprout, buckwheat, cabbage, carrots, cottonseed, forage grasses, forage legumes, kale, kohlrabi, linseed, maize, mangold beet, mustard, oat, parsnip, peanut, potato, rape, rice, rye, sorghum, soybean, sugar beet, sunflower, swede, turnip, wheat. Sheep and goats: barley, brussel sprout, buckwheat, cabbage, carrot, forage grasses, forage legumes, groundnut, kale, kohlrabi, linseed, maize, mangold, mustard, oat, potato, rape, rye, sorghum, soybean, sugar beet, swede, turnip, wheat. According to another aspect, the present invention provides the use of an anti-parasitic protein against an animal parasite, which is preferably an inhibitor of an enzyme of the parasite, for example an inhibitor of a digestive enzyme of the animal parasite, for the manufacture of a composition suitable for administration to the host animal as a medicament or as a food for combating the parasite. According to a further aspect the invention provides the use of a transgenic plant transformed with DNA encoding an anti-parasitic protein against an animal parasite, which is preferably an inhibitor of an enzyme of the parasite, for example an inhibitor of a digestive enzyme of the animal parasite, and capable of expressing the protein within the transgenic plant for the manufacture of a composition suitable for administration to the host animal as a medicament or a food for combating the animal parasite. According to a still further aspect, the invention provides a composition adapted for oral, parenteral or topical administration to a host animal which comprises an anti-parasitic protein directed against a parasite to which the host animal is or may be subject, preferably an inhibitor of an enzyme of the parasite, the anti-parasitic protein having been expressed by a transgenic plant. The composition is preferably adapted for oral administration and may be in the form of a food for the host animal, or in t h e form of a drug or medicament. According to another aspect, the present invention provides a composition adapted for oral, topical or parenteral administration to a host animal as a medicament or a food which comprises a cysteine protease inhibitor from maize or rice as an anti-parasitic protein. The invention also provides a transgenic plant transformed with DNA encoding an anti-parasitic protein against an animal parasite in a form capable of expressing the protein within the transgenic plant, wherein the anti- parasitic protein is a cysteine protease inhibitor from maize or rice and the plant is a dietary crop for the host animal. The animal parasite is preferably a helminth or a protozoan. The parasite may be of the nematode genus Aεcaridia or Aεcariε . For example the animal parasite may be a member of the Order Ascaridata including Aεcariε εuum, Aεcariε lumbricoides, Ascaridia galli , Aniεakiε spp, Paraεcariε equoru , Toxocara caniε, T cati , T vituloru and Toxaεcaris leonina . The animal parasite may also be a trichostrongyle including Nematodiruε battuε, Nematodiruε εpathiger, Nema todiruε filicolliε , Haemonchuε contortus , Trichoεtrongyluε colubriformiε, T tenuiε, T capricola, T falcatuε, T rugatuε, T axei , Oεtertagia oεtertagi , 0 circumcincta, 0 trifurcata, Oeεophagoεtomum radiatum and Cooper a cuticei . The animal parasite may also be a strongyloid including Ξtrongyloideε stercoraliε, S ransomi and 5 papilloεuε . The animal parasite may also be a hookworm including Necator americaniε, Ancyloεtoma duodenale, A ceylanicum, A brazilienεe, A caninum and Bunostomum spp. The animal parasite may also be a metastrongyle including Dictyocaulus viviparis, D filaria, D arnfieldi and Angioεtrongyluε cantonensiε . The animal parasite may also belong to the Order Trichurata including Trichuriε trichuria, T εuis , T ovis, Capillaria hepatica, C annulata, C caudinflata, Trichinella εpiraliε and T pεuedoεpiraliε . The animal parasite may also be an oxyurid including Heterakiε gallinarum, Oxyuriε equi , Enterobiuε vermicularis and E gregorii . The animal parasite may also be a guinea worm including Dracunculuε medinenεis . The animal parasite may also be a filarial worm including JVuchereria bancrofti , Brugia malayi , Onchocerca vovulus, 0 gutterosa , 0 gibεoni , Loa loa , Dipetalonema perεtanε, D εtreptocerca, Manεonella ozzardi and Dirofilaria imitiε . The animal parasite may also be a tapeworm including Taenia solium, ' T εaginata , Diphyllobothrium latum, Ξchinococcuε granulosuε, E hydatigena , Hymenolepiε diminuta and H nana . The animal parasite may also be another helminth including Schiεtosoma mansoni , S haematobium, S japoni cum, S mekongi , S matthei , S intercalatum, S boviε , Faεciola hepati ca, F gigantea , Faεciolopεiε buεki , Dicrocoelium . . dendriticum, Chlonorchiε εinenεis and Opisthorchis felineuε. The animal parasite may also be a protozoan, including coccidia and amoeba. For example the animal parasite may be a coccidian including Eimeria acervulina, E necatrix, E maxima, E brunetti, E tenella, E meleagrimitiε, E danailova, E anεeriε, E alabamenεiε, E boviε, E zuernii, E ahεata, E arloingi, E debliecki, Iεoεpora belli, Toxoplaεma gondii, Sarcocyεtiε hirεuta, S porcifeliε, S cruzi, S tenella, S bertrami, S fayeri, S meiεcheriana, S εuihominiε, S hominiε, S gigantea, Beεnoita bennetti, B wallacei, Hammondia heydorni and Crypto poridium spp.. The animal parasite may also be an amoeba including Entamoeba hiεtolytica, E hartmanni, E gingivaliε, E coli, Endolimax nana, Naegleria fowleri and JodamoeJba buetεchlii. The animal parasite may also be an intestinal flagellate including Giardia inteεtinaliε, Hexamita meleagridis , Hiεtomonaε meleagridiε , Trichomonaε gallinarum, Spironucleuε meleagridiε and Dientamoeba fragiliε. The animal parasite may also be another protozoan including Trypanoεoma brucei, T brucei brucei, T brucei gambienεe, T brucei rhodeεiense, T congolenεe, T vivax, T cruzi, T equiperdu , T equinum, T evanεi, T rangeli, T theileri, Leiεhmania tropica, L tropica tropica, L tropica major, L aethiopica, L donavani, L donavani donavani, L donavani archibaldi, L donavani infantum, L donavani chagaεi, L mexicana, L mexicana mexicana, L mexicana amazonenεiε, L mexicana pifanoi, L mexicana ariεtedeεi, L mexicana garnhami, L brazilienεiε, L braziliensis brazilienεiε, L brazilienεiε guyanenεiε, L brazilienεiε panamenεiε, L peruviana, L enriettii, L hertigi, L hertigi hertigi, L hertigi deanei, L aethiopica, Trichomonaε vaginalis, T tenax, T foetuε, Pentatri cho onaε hominis, Plasmodium vivax, P falciparum, P ovale, P malariae, P gallinaceum, Babesia bigemina , B bovis, B berbera, B divergens, B argentina, B major, B caballi , B equi , B ovis, B motaεi , B traumanni , B caniε , B gibεoni , B feliε, Theileria parva, T annulata, T mutanε, T hirei , T εergenti , T hirci , T oviε and Haematoxenuε veliferouε . The invention is based on the experimental work described in the following Examples. Part of this work is based on Aεcarida galli which is a parasite of chicks. Whilst Aεcarida galli itself is not of particular economic importance as a parasite, the related human and pig roundworms (Aεcariε lumbri coides and Aεcariε εuum respectively) are major world parasites. A . galli represents a suitable experimental model for the validation of the concept on which the present invention is based and demonstrates the applicability of this model to nematodes in particular and other animal parasites in general. In the examples, reference is made to the accompanying drawings in which: Figure 1 shows papain proteolytic activity is inhibited by certain fractions of maize proteins eluted from CM-Sepharose. Figure 2 shows maize proteins eluted from CM-Sephadex in a NaCl gradient. Figure 3 shows inhibition of coloration due to papain activity by maize eluted proteins obtained by the bulk extraction method ' . Figure 4 shows fluorescence caused by cysteine proteinase activity of Aεcaridia galli in fractions of a worm homogenate passed down a Q-Sepharose ion-exchange column. Figure 5 shows protein content of A . galli fractions used in Fig. 4. Figure 6 shows the effect of no inhibitor, E64 and the maize inhibitor preparation on proteolytic activity of A. galli . Figure 7 shows the influence of pre-treatment of maize inhibitor by digestive enzymes and pH condition of the mammalian digestive system on its ability to inhibit papain. Figure 8 shows the effect of maize inhibitor on A. galli incubated in vi tro for 4 days at 37°C in the dark. Figure 9 shows no effect of maize inhibitor on growth rates of chicks. Figure 10 shows a probit curve relating to the mortality of larvae of C. eleganε to the oryzacystatin concentration in the medium from which it feeds. Figure 11 shows changes in total weight of A . galli for chicks fed either on untransformed Arabidopεiε or this plant expressing a low level of oryzacystatin I. Example 1 - Extraction of a cystatin from plants to demonstrate effects on parasites Maize meal was stirred overnight at 4°C in 50mM Na acetate buffer (pH 5.0) and centrifuged for 30 min at 15,000 g. The supernatant was put on a CM Sepharose column (10 x 1 cm) equilibrated with acetate buffer (pH 5.0) . The column was washed with acetate buffer and proteins eluted by a linear gradient system of NaCl (0-1M) in 50mM Na acetate buffer (pH 5.0). 1 ml fractions were collected and tested for inhibition of papain using the papain-specific chromogenic substrate, p-Glu-Phe-Leu-p-nitroaniline. The inhibition of papain was investigated by dissolving 0.5 mg/ml papain in 50 mM Tris-HCl at pH 7.5 and 100 μl placed in individual wells of a microtitre plate (NUNC) and incubated overnight at 4°C. After several rinses of the plates in phosphate buffered saline (PBS) , papain coated to the plate was activated for 20 min with 0.1M 2- [N- morpholino]ethanesulphonate (MES-OH) pH6 containing 4mM dithiothrietol (DTT) and 4mM EDTA. These prepared plates were used for inhibition assays. 100 μl aliquots of the eluted zeacystatin preparation from CM Sephadex chromatography were added and incubated for 30 min at 37°C. The plates were rinsed thoroughly in PBS (10 mM Na 2 P0 4 /KH 2 P0 4 + 0.14M NaCl) before 100 ml 50 mM p- Glu-Phe-Leu-p-nitroaniline in 50 mM MES-OH (pH 6) containing 2 mM DTT and 2 mM EDTA was added. The colour was allowed to develop before absorbance was measured at 405 nM using a microtitre plate reader (Biorad) . Blanks consisted of wells without coated papain. The most active fractions (eluted between 0.2-0.3 M NaCl) were pooled and dialysed extensively against 0.1M KH 2 P0 4 /K 2 HP0 4 buffer (pH 7.0). Maize inhibitor was purified by affinity chromatography using carboxymethylpapain-Sepharose made according to the method of Anastasi et al (1983) . Pooled maize fractions were loaded onto the column previously equilibrated with phosphate buffer (pH 7.0), and the solution allowed to percolate. Unbound protein was removed by washing with 10 column volumes of phosphate buffer (pH 7.0) . Inhibitor was eluted with 2 column volumes of 75mM K 3 P0 4 (pH 11.5) containing 0.1M NaCl and the 1.0 ml fractions quickly adjusted to pH 7.5 with 3M Na formate/formic acid buffer (pH 3.0) prior to dialysis against distilled water. Figure 1 shows the effect of fractions on coated papain activity using p-Glu-Phe-Leu-p-nitroaniline as substrate. As shown by this figure, the fractionation of maize meal protein on CM Sepharose revealed major papain inhibitory properties between fractions 20-28 and a minor inhibition for fractions 42-44; the latter effect was not studied further. Figure 2 shows the CM Sephadex C50 chromatography profile of acid-soluble maize proteins eluted with a linear gradient of NaCl. Fractions eluted in 0.2 to 0.4 M NaCl were used to assay for protease inhibitors (Abe and Arai, 1985; Abe and Whittaker, 1988) . This information was used to devise a larger-scale method for extracting sufficient material for subsequent experiments. The protease inhibitor was extracted in bulk from maize meal (pollenta medium, Smith Flour Mills, Worksop, Notts., UK) using a batch technique. 5 kg of maize meal was extracted in 15 litres of 50 mM Na acetate buffer (pH 7.0) for 4 h at room temperature. The mixture was filtered through 4 layers of muslin, adjusted to pH 5 with acetic acid and left overnight at 4°C. The supernatant (about 9 litres) was siphoned into a container containing 3 litres of CM Sephadex previously equilibrated with 50 mM Na acetate buffer (pH 5.0) and the mixture gently agitated for 3h at 4°C. The mixture was poured through a 30μm mesh filter and the retained Sephadex washed extensively with 50mM acetate buffer (pH 5.0). 1.5 litres of 50 mM acetate buffer (pH 5.0) were added and the mixture gently agitated for 3 h at 4°C. 1.5 litres of 50mM acetate buffer (pH 5.0) containing 0.2M NaCl was added to the gel and allowed to equilibrate for 20 min with gentle agitation. The liquid was removed by filtration through 30μm mesh and discarded. The Sephadex was re-treated with 1.5 litres acetate buffer containing 0.4M NaCl and the supernatant (about 1.2 litres) containing eluted proteins was kept. Ammonium sulphate was added to 80% (w/v) and the precipitate collected by centrifugation at 10,000 g for 15 min, and re-suspended in 50 ml of distilled water. Salts were removed by dialysis against distilled water overnight at 4°C. The dialysed solution containing inhibitor was tested for activity with papain. The final elutant between 0.2-0.4 M NaCl from CM-Sephadex in this larger scale preparation was tested for potency against papain. For this test, 50μl of l.5μg/ml papain was added to 50μl of 62μg/ml or 46.5μg/ml or 31μg/ml of the eluant protein for 20 minutes before addition of substrate. Figure 3 shows the effect of partially purified inhibitor from maize (large scale batch method) on the activity of papain (100% = undiluted inhibitor; 0% = no inhibitor) . Undiluted CM-Sephadex fraction contained 31μg of inhibitor in lOOμl. From Figure 3 it can be seen that undiluted CM-Sephadex extract almost completely blocked papain activity and 30% inhibition was obtained with 15.5μg zeacystatin/lOOμl (i.e. 25% in Figure 3) . Example 2 - The protease activity of animal parasites Ascaripain from Aεcariε suum is similar to Ascaridia cysteine protease. Both prefer hydrolysis of Z-Phe-Arg-aminomethylcoumarin and both have limited action on Z - Phe-Arg-Arg-aminomethy1coumarin and Bz-Arg-aminomethylcoumarin. Both proteases are highly sensitive to egg white cystatin, E64 and zeacyεtatin and both are stimulated by EDTA/DTT. Pepstatin and serine protease inhibitors have no effect. Cysteine proteases were extracted from whole Ascaridia galli obtained from the small intestine of chicks, snap frozen in liquid nitrogen and stored at -70°C until required. 4g of frozen worms were homogenised in 40 ml of 30 mM Tris-HCl (pH 7.5) buffer (TB) , centrifuged at 20,000 g for 30 minutes at 4°C and the resultant supernatant mixed with 5 ml Q-Sepharose (fast flow) previously equilibrated with TB. The mixture was gently stirred overnight at 4°C and the matrix poured into a 10 x 1 cm column and allowed to drain. The gel was washed with 15 column volumes of TB with a flow rate of 1ml min *1 . Proteins were eluted with a 0-1M NaCl gradient in TB. 1 ml fractions were collected and assayed for cysteine protease activity with the specific fluorogenic substrate Z-Phe-Arg-aminomethylcoumarin (Z-Phe-Arg-AMC; Sigma) . A 50μl sub-sample of each fraction from column chromatography was added to 50μl of 0.1M MES-OH (pH 6.0) containing 2mM EDTA and 2mM DTT (MED) and 50 M of Z-Phe-Arg-AMC (first dissolved in DMSO) . The solutions were mixed and placed in wells of a 96 well microtitre plate (NUNC) and viewed under UV light after 30 min incubation at 37°C. Wells of the microtitre plate with a fluorescent product signified presence of proteolytic activity in the corresponding fraction from which the 50 μl sub-sample was derived. The main fractions giving rise to the principal fluorescence were pooled, dialysed against MED buffer and used for inhibition studies. Protein concentration was assayed according to Bradford (1974) . 60μl of dialysed pooled cysteine protease fraction derived from A . galli was added to (i) 30 μl of distilled water (ii) 10 μM E64 or (iii) 30 μM zeacystatin and pre-incubated for 20 min at 37°C. 50 μM of Z-Arg-Phe-β- naphthylamine was added and the reaction terminated after 20 min with 100 μl of Fast Garnett reagent containing Mersalyl acid and Brij 35 (Barrett and Kirschke, 1981) . The resultant optical density due to protease activity was measured at 490 nm using a micotitre plate reader (Biorad) . Proteolytic activity of eluted worm fractions from Q-Sepharose chromatography was monitored in a microtitre plate with Z-Phe-Arg-AMC. Figure 4 shows fluoresence of fractions viewed with UV light from Q Sepharose chromatography after incubating with Z-Phe-Arg-AMC. Fluorescence in wells indicates proteolytic activity (cathepsin L-lik ' e enzymes) . Cysteine proteases were detected between fractions 9-19, with peak proteolytic activity found between fractions 12-15. Figure 5 shows protein content (indicated by the solid line with square symbols) of fractions obtained from Q-Sepharose ion-exchange chromatography. The dashed line represents proteolytic activity in fractions 9 to 19 with peak activity found in fractions 12 to 15 (thick line) . The solid line without symbols indicates NaCl levels of the eluant. The activity corresponded with the second peak of eluted protein which came off at 0.23-0.28 M in the NaCl gradient. The most active fractions were pooled, dialysed against MES-OH (pH 6.0) buffer containing DTT and EDTA and assayed with E64 or zeacystatin. A single band of about 13 KDa was visualised after SDS-PAGE and staining for protein with Commassie Blue. Figure 6 shows the effect of inhibitors on the activity of protease from Ascaridia galli . Controls containing no inhibitor indicate a relative activity of 100% towards Z-Phe-Arg-β-napthylamine and is represented by an absorbance of 0.6 OD units. E64 inhibited proteolytic activity by over 90%, whilst the zeacystatin curtailed proteolysis by 65%. A single band of about 13 KDa was seen on SDS-PAGE as before. The use of a cysteine protease-specific substrate, together with inhibition of the enzyme by E64, confirms the presence of cysteine proteases in A. galli with properties not dissimilar to those of cathepsin L from a range of parasitic organisms and Ascaripain from A. εuum (Koritsas, unpublished) . Example 3 - Test to show protease inhibitors can withstand physiological conditions occuring in the alimentary system of livestock and humans. The orally administered protective agent must retain its efficacy after passage through the alimentary system to its site of action against the parasite. An experiment was therefore carried out to demonstrate that certain protease inhibitors are capable of retaining their efficacy after exposure to the enzymes that digest proteins in the mammalian alimentary system. Figure 7 shows the action of "gut-enzyme-treated" maize inhibitor on the activity of papain. Absorbance of 0.49 represents 100% papain activity. In Figure 7, 1 = papain only, 2 = papain + untreated inhibitor, 3 = papain + enzyme- reated inhibitor; 4 = buffer only + treated inhibitor; 5 = papain + enzyme mixture only. The example shows the ability of zeacystatin to withstand challenge by proteolytic enzymes of the stomach in a highly acidic environment and then to withstand hydrolytic enzymes found in the more alkaline pHs of the intestine. 50μl of 0.1 mg/ml zeacystatin was mixed with 25μl pepsin (2μl/ml) for 90 minutes at pH 2.0 (37°C) before being inactivated by increasing the pH to 8.0 with 3M NaOH. 25 ml of an enzyme cocktail containing 5 mg/ml of each of trypsin, chymotrypsin and elastase in 50 mM Tris-HCl (pH 8.0), 2mM CaCl 2 was then added and incubated further at 37°C for 90 min. The enzymes were inactivated by bringing down the pH to 1.5 with 1 M HC1 and left for 30 min at 4°C. The mixture was centrifuged and the supernatant brought to pH 6.0 with NaOH. Zeacystatin was assayed for inhibition with papain at a 1:1 molar ratio in buffer (pH 6.0) containing 2 mM DTT and 4 mM EDTA. The inhibitor and enzyme were preincubated for 15 min at 37°C prior to addition of papain substrate (50 μm p-Glu-Phe-Leu p-nitroaniline) and incubated for a further 30 min. Controls were treated similarily but zeacystatin was not added at the start of the reaction. Absorbance was read at 405 nm as before. No apparent effect was seen on inhibitor activity which remained very effective in reducing papain activity. Example 4 - Evidence for the effect of protease inhibitors on animal parasitic nematodes held in vitro 35 day old Aεcaridia were removed from the host and thoroughly rinsed with 0.9% (w/v) NaCl in distilled water before transfer to 3 cm plastic Petri-dishes containing basic culture medium: CaCl 2 2H 2 0 (0.24 mg/ml), Na 2 HCϋ 3 (0.2 mg/ml), NaCl (9.0 mg/ml) and D-glucose (1 mg/ml). Streptomycin sulphate (100 mg) and penicillin (60 u) were included to reduce microbial contamination. Three treatments of five replicates containing 4 worms each were used to assess the potency of the maize inhibitor. Each treatment was carried out in the basal culture medium supplemented with: (i) 0.5mg/ml bovine serum albumin (BSA); (ii) 0.5mg/ml maize protein recovered by the batch method of which zeacystatin was estimated to be at 22μg/ml; (iii) no supplement to the medium. The worms were kept for 4 days in the dark at 37°C and solutions changed daily. Zeacystatin concentration was estimated using a papain inhibition assay as previously and by comparison of the inhibition derived from the batch method with that achieved for the zeacystatin obtained by affinity chromatography earlier. Worms cultured in basic medium and that supplemented with BSA remained active for 4 days at 37°C. Most worms in the maize proteins enriched for the inhibitor were dead but a few were inactive but responsive to a tactile stimulus. These observations were quantified and expressed as activity scores for each individual on the following limited scale: 0 (dead) , l (inactive but responsive to a tactile stimulus) , 2 (intermittant activity) to 3 (frequently active) . The results are presented in Table 1 which shows a clear effect of the preparation containing zeacystatin on the viability of the nematodes in vi tro . . TABLE 1 Effect of Maize inhibitor after 4 days on the activity and general appearance of A. galli maintained in basic medium in the dark at 37°C No Inhibitor Inhibitor BSA Activity 3.00 ± 0 0.85 ± 0.65 2.75 ± 0.35 Score Figure 8 shows the general appearance of A . galli after 4 days treatment with inhibitor and BSA in the dark at 37°C. This work establishes that maize meal contains an inhibitor capable of affecting the well-being of whole worms in culture. This finding establishes that a preparation of maize proteins enriched for zeacystatin is capable of inducing lethargus leading to mortality in A . galli . Example 5 - Evidence for in vivo effect of protease inhibitors on animal parasitic nematodes within hosts Two-week old chicks were paired according to their body weight and housed in eleven cages each containing two birds on concrete floors covered with wood shavings at 15-22°C. Food and water were available ad libi tum . Two days prior to infection of the chicks with A. galli , the birds were injected (and every 10 days thereafter) in the thigh with an immunosuppresant, (Depo-medrone - Upjohn) . This was necessary to ensure a high worm burden in the chicks. Birds were weighed and each was inocculated orally with 100 embyronated eggs of A. galli in 0.1 ml distilled water. Three days after infection, one chick from each cage was dosed orally with 0.5 ml water from a syringe and the other treated similarily with 1 mg of the batch isolated maize proteins containing 22 μg zeacystatin in 0.5 ml water. The dose was given daily until one day before sacrifice of the birds. Birds were weighed, sacrificed and the worm burden removed from the small intestine. The nematodes were rinsed with water and placed in fixing solution containing 2 ml triethanolamine, 7 ml formalin (40% formaldehyde) and 91 ml distilled water. Parasite length and width were determined by placing the animals on a graticule overlayed with acetate sheeting. They were viewed under a stereobinocular microscope with reflective lighting and their length and maximum width recorded. Measurements of the reproductive systems of females were made as an indicator of reproductive development. Reproductive structures were gently removed with dissecting needles, placed on acetate and the length of the female reproductive system recorded. The ratio of the female reproductive structures to worm length was calculated. Figure 9 shows the effect of maize inhibitor on the growth rate of chicks. Birds fed on maize inhibitor showed no ill effects and continued to grow at the same rate as the controls. The feeding behaviour and water uptake of both groups showed no differences. All three measurements on parasite body length, width and volume revealed significant reductions (Table 2) . The inhibitor reduced worm length, width and volume, by 10, 13 and 32% respectively. Values were estimated from measurements of length and maximum width using a standard formula (Andrassy, 1956) . TABLE 2 The effect of partially purified inhibitor on the size of A. galli growing in chicks after 28 days treatment. Values represent means ± sd of over 100 replicates Parameter Control Inhibitor Significance Length (mm) 51 ± 2.5 46 ± 1.5 P < 0.001 Width (mm) 0.83 ± 0.04 0.72 ± 0.02 P < 0.05 Volume (mm 3 ) 20.67 ± 1.2 14.03 ± 0.07 P < 0.001 The length of the ovaries housing the developing eggs was highly significantly reduced (P < 0.001) in worms from chicks treated with zeacystatin (Table 3) . Even when taking body length into account, the effect was still highly significant both in absolute lengths and as a ratio to body length. TABLE 3 Effect of partially purified inhibitor on the reproductive structures of A. galli after 28 days treatment of chicks. Values represent means ± sd of 24 replicates Control Inhibitor Significance Uterus (mm) 67.0 ± 7.0 41.0 ± 18.4 P < 0.001 Uterus: 1.25 ± 0.12 0.81 ± 0.33 P < 0.001 female Body length This work demonstrates that normal growth and development of A. galli was affected by the uptake of zeacystatin by the host. This requires the inhibitor to remain active after oral administration and to be taken up by the parasite within the intestine. This uptake in the experimental system is sufficient to have effect on the growth and development of the parasite. Therefore the effects established in examples 1-3 are substantiated with the results in example 4. The suppression of growth of A. galli was achieved with necessarily low levels of zeacystatin because of the need to recover the inhibitor from a low concentration within maize meal. The clear effect were achieved with doses of only 22 μg/day of zeacystatin. This is a small fraction of that available via the diet given expression levels of 1-2% total soluble protein is often achieved for transgenes in plants including a protease inhibitor (Hepher & Atkinson, 1992) . Such levels could be delivered in as little as ll-22mg of dry food/day. This is only 0.005-0.05% of the daily food intake of the birds and gives scope for considerable increase in the daily dose rate once the inhibitor is expressed in experimental transgenic plants with a constitutive promoter such as Cauliflower mosaic virus 35S promoter. Example 6 - Extraction of cloned cystatin and evidence for an in vitro effect on animal parasitic protozoa in culture Preparation and manipulation of DNA Plasmid DNA was purified from E. coli cultures by the alkaline lysis method (Sambrook et al., 1989) . Restriction digests and ligation reactions were carried out using the recommendations of the manufacturer of the relevant enzymes. DNA fragments were recovered from agarose gels using an εlectroelution chamber (IBI) following the manufacturer s protocol. Oligonucleotides were synthesised on an Applied Biosystems 381A instrument. DNA sequencing of double stranded plasmid DNA was performed using Sequenase version 2.0 (Amersham) , according to the manufacturer s instructions. Cloning of the cystatin Oc-J was amplified from genomic DNA of Oryza εativa L . j aponi ca with primers PI and P 2 designed from published sequence data (Abe et al, 1987) and with the addition of restriction enzyme sites to assist cloning. The intron was removed using the PCR technique of SOEing (Horton et al 1989) using primers P1/P3 and P2/P4 to amplify the two exons. These were then SOEn together by amplifying with primers PI and P4. The SOEn product was cloned into Sma I / Eco RI pBluescript. The sequence of the cloned coding region was verified by comparing with the published data for Oc-J (Abe et al 1987) . The sequences of primers PI to P4 are shown as follows: Primer PI SEQ ID NO. 1 Primer P2 SEQ ID NO. 2 Primer P3 SEQ ID NO. 3 Primer P4 SEQ ID NO. 4 Expression of Oc-J Oc-I expressed from pQE30 ( QIAexpress system) contained six N-terminal histidine residues, encoded by the vector to allow one-step Nickel chelate affinity. Oc-I protein was purified from 1 litre cultures of E. coli Ml5[pREP4] harbouring the pQE30 derived expression plasmid. 20 ml overnight cultures were used to inoculate 1 litre of LB media and grown at 37°C to A 600 0.7-0.9. IPTG was added to a final concentration of 2 mM and growth was allowed to continue for a further 2 h. The cells were harvested by centrifugation at 10,000g for 10 min. The cells were re- suspended in a total volume of approximately 12 ml of sonication buffer (50 mM Na 2 HP0 4 , 300 mM NaCl) and stored at -20°C overnight. The sample was thawed and aliquoted to three 15 ml tubes and sonicated on ice in short pulses (3x30 sec). Cell debris was pelleted by centrifugation (10,000g) and approximately 0.5-0.75 ml of Ni-NTA resin slurry (Qiagen, California, USA) was added to each tube and mixed gently on ice for 1 h. The resin was collected (1000 g for 1 min) and washed with 5 ml of buffer (50 mM Na 2 HP0 4 pH 6.0, 500 mM NaCl, 40 mM imidazole at 4C for 0.5h). Protein was eluted with 1 ml of elution buffer (50 mM Na 2 HP0 4 , 300 mM NaCl, lOO M EDTA) and the resin was re-pelleted at 1000 g for 1 min and the elution repeated a further two times. The purified proteins were analysed by SDS-PAGE (Hames 1981) and only one protein was detected on these gels (Commassie staining) and following Western blotting using the polyclonal antibody prepared against this protein (see below) . Antibody production Oc-I antibodies were raised in male Wistar rats (6 weeks old) which were immunised intraperitoneally. Three injections were given at four week intervals of 100 μg Oc-I recovered from the pQE30 expression system in a final volume of 300 μl. The first injection was an emulsion of protein and complete Freund s adjuvant in a 1:1 (v/v) ratio and the second and third injection were similar but used incomplete Freund s adjuvant. Ten days after the final injection, blood was collected and allowed to coagulate at 4 °C before centrifugation at 5000 g for 10 min. The resultant serum was collected and stored at -20°C in glycerol. The antibody gave optimal results in ELISA at a dilution of 1 in 10000 and recognised both native and denatured protein. Tachyzoites of T. gondii were produced by intraperitoneal passage in Tuck's Number 1 outbred mice, approximately 10 7 parasites are injected intra-peritoneally and parasites for culture were harvested three days later by peritoneal lavage with F12 medium and used immediately. MDBK cells were plated onto 13mm cover-slip cultures at a density of 1x10 s per cover slip and incubated overnight in HAM's F12 medium (GIBCO) plus 10% foetal calf serum at 37°C. Tachyzoites of RH strain Toxoplaεma gondii (2xl0 6 ) were loaded onto each cover slip and incubated for 4 hours at 37°C to allow invasion of the MDBK cells. Cultures were then washed with F12 medium to remove extracellular parasites and the inhibitor was added at a concentration of 0, 30 or 120 μg/ml. The cultures were incubated for a further 24 hours at 37°C and then removed, washed with PBS, fixed with Bouin's solution and stained with Geimsa. Parasite growth was assessed by scoring approximately 200 cells for the number of infected cells and the total number of parasites in the sample. The percentage of MDBK cells infected with T. gondii fell from 76 ± 9 in the control to 66 ± 2 and 59 ± 0.6 with increasing concentration of inhibitor. The number of T. gondii was 4.2 ± 0.17 per host cell when an inhibitor concentration of 120μg/ml was used. This was a significant reduction (P<0.05 Analysis of variance, linear combination, Snedecor and Cochrane, 1989) in the number of T. gondii per host cell compared with a lower concentration of 30 μg/ml of the inhibitor and the control respectively (see Table 4 below) . TABLE 4 Example 7 - Anti-nematode effect of cystatin when ingested by a nematode Cysteine proteinases have been reported from animal parasitic nematodes (Sakanari, 1990; Healer et al 1991; Cox et al 1990; Pratt et al 1990) but feeding trials are not readily carried out using obligate parasites. In situ hybridisation has demonstrated transcripts of cysteine proteinases are abundant in the intestine of the bacterial feeding nematode Caenorhabdi tiε eleganε (Ray and McKerrow, 1992) . This animal can be fed and reared on E. coli on media to which proteins of interest can be added. Therefore we have used this system to gain insights into the probable mode of activity of a cystatin against nematodes. This work involve cloning a previously described cystatin from rice (Abe et al 1987) and expressing it in a bacterial expression vector. The expressed protein was recovered and used to add to the agar from which E. coli fed. Challenging C. elegans with a cystatin Caenorhabdi tiε eleganε was cultured on NGM agar carrying a lawn of OP50 E. coli as described by Wood (1988) . Populations were maintained for 5 days after which time an agar plug from the colony plate was inserted onto fresh media. When required, the Oc-I (see Example 6) or BSA was added to the cooled medium to a final concentration of 2.5 mg l "1 just before polymerisation. Single nematodes were transferred from non-supplemented solid agar plates to plates containing Oc-I or BSA. In vivo testing against C. eleganε Feeding trials were set-up using C. eleganε to examine the effect of Oc-I on nematode survival and growth. As soon as hermaphrodites became apparent on normal agar they were transferred to individual plates containing either Oc-I or BSA and egg laying was observed. Ten replicates were carried out for each condition. Irrespective of the culture conditions the hermaphrodites laid a mean of 300 eggs. Greater than 95% of the eggs hatched even when a cystatin was present in the medium. Of the larvae hatched from eggs on BSA, and Oc-I supplemented media and then transferred to normal media, 96.0%, and 97.0% completed development. Of the larvae hatched and left to develop on cystatin- supplemented media less than 2% of the larvae achieved normal development to adulthood, in contrast to 95% of corresponding larvae exposed to BSA-supplemented media. Subsequently the larvae hatched under normal conditions were removed to media supplemented with either Oc-I or BSA. 50 larvae were removed at 6 h, 12 h, 24 h and 30 h (corresponding to the four larval stages LI, L2, L3 and L4 respectively) . Of the larvae transferred 6, 12 or 24 h after hatching (on normal media) to media supplemented with Oc-I, none developed further to reach the mature adult stages. 76 % of larvae allowed to develop on normal media for 30 h after hatching prior to transfer to Oc-I supplemented media carried on their development and reached adult male or hermaphrodite stages. The remainder of these larvae (24 %) did not reach the adult stages of development. All juveniles hatched from eggs laid on media containing BSA and transferred to normal media developed into adult nematodes. Larvae of C. eleganε were transferred to agar plates with E. coli in which the medium was supplemented with 0-10 mg/L of Oc-I and the subsequent mortality of the animals during feeding was estimated from activity of the animals. The data was subject to probit analysis from which a value for LD50 was derived of approximately 7mg Ocl per litre of medium. Figure 10 shows a probit curve relating the mortality of larvae of C. eleganε to the oryzactstatin concentration in the medium from which it feeds. Some C. eleganε larvae which failed to develop on Oc-I plates were transferred to fresh media not supplemented with the cystatin and observed for signs of recovery. The larvae failed to respond to the fresh food source and showed no signs of further development. These larvae also failed to respond to being touched, exhibiting no signs of movement following repeated stimuli indicating mortality and not dauer larvae formation. These experiments established that a cystatin was only lethal to the nematode when actively feeding and growing. It did not prevent hatching or kill adult nematodes. The latter have completed the period of rapid growth that precedes sexual maturity. They may have sufficient endogenous reserves to ensure that further dietary intake of protein is not essential for their survival. Alternatively, the adult may have other than a cysteine proteinase in its intestine. Given the known presence of a cysteine proteinase in the intestine of larvae and the correlation between anti-parasitic effects of a cystatin and feeding, it seems likely that it is the intestinal digestion of protein that is disrupted in A . galli by a cystatin in other examples given in this application. Example 8 : Anti-parasitic effect of a cystatin when expressed in plant material that is fed to the host These experiments used Oc-I to produce transgenic Arabidopεiε expressing the cystatin constitutively. The fresh plant material was then used as supplement in the food of chicks that had been previously infected with A. galli . The objective was to confirm that a cystatin had the beneficial anti-parasitic effect already established by oral dosing in aqueous media when administered within the food of the host. Transgenic Arabidopsis Oc-I was cloned from within pBluescript into the vector pBIN19 (Bevan, 1984) using standard procedures (Maniatis et al . , 1982) to produce a chimeric gene construct under control of the Cauliflower Mosaic Virus 35S promoter (Guilley et al . , 1982). This promoter is generally constitutively active in plant tissues (Odell et al . , 1985) . Gene constructs for transformation were transferred to Agrobacterium tumefacienε by electro-transformation (Wen-Jun and Forde, 1989) . Root explants of Arabidopεiε thaliana ecotype C24 were transformed essentially as described by Valvekens et al. (1988) with modifications to the procedure as described by Clarke et al . (1992) . Aseptically grown roots were excised and pre-incubated for 2-3 days on an agar-solidified medium containing plant growth regulators for callus-induction before being cut into approximately 0.5 cm explants and inoculated with Agrrojacterium. Following 2 days of co-cultivation with the bacteria, explants were transferred to shoot-inducing medium and after 10-14 days transformed plants began to regenerate. Regenerated plants were individually transferred to plant growth regulator-free medium and allowed to set seed in vitro. The resulting seeds were used to bulk up stocks and the subsequent generation used for feeding experiments. Seeds were sown in standard seed trays and grown under glasshouse conditions. Seeds of non-transformed Arabidopεiε were similarly sown. Chicks were supplied with rooted, intact, fresh plant material as a supplement to their normal feed. Observation established that this plant material was consumed in preference to their concurrently supplied normal food. The birds did disperse some of their food and so consumed less than their daily supply of Arabidopεiε . Anti-parasitic effects of transgenic Arabidopsis provided to chicks in their feed These exeriments with chicks were carried out with similar experimental conditions to example 5. All were immunosuppressed and infected with Aεcaridia galli as described earlier. Each bird was weighed immediately before infection and birds of similar weights were paired for the two treatments of untransformed and cystatin-expressing Arabi dopεiε . Twelve pairs of chicks were established in this way and two birds of one treatment were housed together to avoid incorrect access to the transgenic plants. They were provided from infection ad libi tum with water and a proprietry chick starter crumb feed and the plant material supplement on a daily basis. Each pair of birds had access to a mean of 448±25 g of Arabidopεiε per week , the majority of which was ingested. After 28 days, the birds were weighed, sacrificed and the A. galli were recovered from their intestine as before. These nematodes from each host were fixed in TAF in a series of containers. They were subsequently counted, blotted on filter paper to remove excess fixative and their total wet weight determined using an analytical balance. The weight of each group of nematodes was plotted as a percentage of that for the largest weight in each of the two treatments. This data is plotted against nematodes per host in Figure 11 which shows changes in weight of A galli as a percentage of the maximum value plotted with linear regression lines against the number of nematodes per host for 24 chicks fed either on untransformed Arabidopεiε (■) or this plant expressing a low level of oryzacystatin I (0) . There was no significant decrease in weight of A . galli with increasing parasitic burden per host for the controls. However this effect did occur for chicks fed on A.rabidopεiε expressing the oryzacystatin and the downward slope of the regression line was statistically significant (P 0.05) . These results establish that even low levels of a cystatin expressed in only a small part of the food intake of chicks is sufficient for an anti-parasitic effect. The results demonstrate the considerable practical utility of this novel approach to parasite control from several standpoints. The results suggest there may be potential for plant material expressing much higher levels of anti- parasitic protein to be used as an additive to normal food rather as the principal form of dietary intake. References ABE, K. and ARAI, S. (1985) . Purification of a cysteine proteinase inhibitor from rice, Oryza εativa L. Japonica. Agricultural and Biological Chemiεtry 49, 3349-3350. 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SEQUENCE LISTING (1) GENERAL INFORMATION: (i) APPLICANT: (A) NAME: The University of Leeds (B) STREET: Leeds (C) CITY: Leeds (E) COUNTRY: Great Britain (F) POSTAL CODE (ZIP) : LS2 9JT (A) NAME: Howard John Atkinson (USA only) (B) STREET: 43 Sutherland Avenue (C) CITY: Leeds (E) COUNTRY: Great Britain (F) POSTAL CODE (ZIP) : LS8 1BY (A) NAME: Vas Michael Koritsas (USA only) (B) STREET: 87 Stainbeck Road (C) CITY: Leeds (E) COUNTRY: Great Britain (F) POSTAL CODE (ZIP) : LS7 2PR (A) NAME: Donald Lewes Lee (USA only) (B) STREET: 970 Scott Hall Road (C) CITY: Leeds (E) COUNTRY: Great Britain (F) POSTAL CODE (ZIP) : LS17 6HH (A) NAME: Andrew Neilson Macgregor (USA only) (B) STREET-. 12 Carr Manor Drive (C) CITY: Leeds (E) COUNTRY: Great Britain (F) POSTAL CODE (ZIP) : LS17 5AU (A) NAME: Judith Elisabeth Smith (USA only) (B) STREET: 15 St Chad's Drive (C) CITY: Leeds (E) COUNTRY: Great Britain (F) POSTAL CODE (ZIP) : LS6 3PZ (ii) TITLE OF INVENTION: Control of Parasites (iii) NUMBER OF SEQUENCES: 4 (iv) COMPUTER READABLE FORM: (A) MEDIUM TYPE: Floppy disk (B) COMPUTER: IBM PC compatible (C) OPERATING SYSTEM: PC-DOS/MS-DOS (D) SOFTWARE: PatentIn Release #1.0, Version #1.30 (EPO) (2) INFORMATION FOR SEQ ID NO: 1: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 31 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: other nucleic acid (A) DESCRIPTION: /desc = "OLIGONUCLEOTIDΞ" (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 1: ACATGTCGAA TTCTTAGGCA TTTGCACTGG C 31 (2) INFORMATION FOR SEQ ID NO: 2: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 24 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: other nucleic acid (A) DESCRIPTION: /desc = "OLIGONUCLEOTIDE" (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 2: GAGGAGCCCG GGTCGAGCGA CGGA 24 (2) INFORMATION FOR SEQ ID NO: 3: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 33 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: other nucleic acid (A) DESCRIPTION: /desc = "OLIGONUCLEOTIDE" (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 3: CTCGAACTCT AGAAGAGAAT TGGCCTTGTT GTG 33 (2) INFORMATION FOR SEQ ID NO: 4: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 18 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: other nucleic acid (A) DESCRIPTION: /desc = "OLIGONUCLEOTIDE" (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 4: AATTCTCTTC TAGAGTTC 18

Claims: CLAIMS : 1. A method for combating an animal parasite in a host animal which comprises delivering an anti-parasitic protein to the parasite or to a locus thereof by administering the protein to the host animal as a medicament or as a food. 2. A method according to claim 1 wherein the anti- parasitic protein is an inibitor of an enzyme of the parasite. 3. A method according to claim 1 or 2 wherein the animal parasite is a helminth or a protozoan. 4. A method according to claim 3 wherein the animal parasite is a nematode. 5. A method according to any of claims 1 to 4 wherein the anti-parasitic protein is an inhibitor of a digestive enzyme of the parasite. 6. A method according to claim 5 wherein the anti- parasitic protein is a cysteine protease inhibitor. 7. A method according to claim 5 wherein the anti- parasitic protein is a cysteine protease inhibitor from maize or rice. 8. A method according to any of claims l to 7 wherein the anti-parasitic protein is expressed by a transgenic plant. 9. A method according to claim 8 wherein the transgenic plant is a dietary crop for the host animal. 10. Use of an anti-parasitic protein against an animal parasite for the manufacture of a composition suitable for administration to a host animal as a medicament or as a food for combating the parasite. 11. Use according to claim 10 wherein the anti-parasitic protein is an inhibitor of an enzyme of the parasite. 12. Use according to claim 11 wherein the animal parasite is a helminth or a protozoan. 13. Use according to claim 12 wherein the animal parasite is a nematode. 14. Use according to any of claims 10 to 12 wherein the anti-parasitic protein is an inhibitor of a digestive enzyme of the parasite. 15. Use according to claim 14 wherein the anti-parasitic protein is a cysteine protease inhibitor. 16. Use according to claim 15 wherein the anti-parasitic protein is a cysteine protease inhibitor from maize or rice. 17. Use according to any of claims 10 to 16 wherein the anti-parasitic protein is expressed by a transgenic plant. 18. Use according to claim 17 wherein the transgenic plant is a dietary crop for the host animal. 19. A composition adapted for oral, parenteral or topical administration to a host animal which comprises an anti- parasitic protein directed against a parasite to which the host animal is or may be subject, the anti-parasitic protein having been expressed by a transgenic plant. 20. A composition according to claim 19 wherein the transgenic plant is a dietary crop for the host animal. 21. A composition according to claim 19 or 20 wherein the anti-parasitic protein is extracted from the transgenic plant prior to incorporation into the composition. 22. A composition according to claim 20 wherein the anti- parasitic protein is incorporated into the composition in the form of parts of the transgenic plant. 23. A composition according to any of claims 19 to 22 wherein the anti-parasitic protein is an inhibitor of an enzyme of the parasite. 24. A composition according to any of claims 19 to 23 in a form adapted for oral administration. 25. A composition according to claim 24 in the form of a food or a medicament for the host animal. 26. A composition according to any of claims 19 to 25 wherein the animal parasite is a helminth or a protozoan. 27. A composition according to claim 26 wherein the animal parasite is a nematode. 28. A composition according to any of claims 19 to 27 wherein the anti-parasitic protein is an inhibitor of a digestive enzyme of the parasite. 29. A composition according to claim 28 wherein the anti- parasitic protein is a cysteine protease inhibitor. 30. A composition according to claim 29 wherein the anti- parasitic protein is a cysteine protease inhibitor from maize or rice. 31. A composition adapted for oral, topical or parenteral administration to a host animal as a medicament or a food which comprises a cysteine protease inhibitor from maize or rice as an anti-parasitic protein. 32. Use of a transgenic plant transformed with DNA encoding an anti-parasitic protein against an animal parasite and capable of expressing the protein within the transgenic plant for the manufacture of a composition suitable for administration to the host animal as a medicament or a food for combating the animal parasite. 33. Use according to claim 32 wherein the anti-parasitic protein is an inhibitor of an enzyme of the parasite. 34. Use according to claim 32 or 33 wherein the animal parasite is a helminth or a protozoan. 35. Use according to any of claims 32 to 34 wherein the animal parasite is a nematode. 36. Use according to any of claims 32 to 35 wherein the anti-parasitic protein is an inhibitor of a digestive enzyme of the parasite. 37. Use according to claim 36 wherein the anti-parasitic protein is a cysteine protease inhibitor. 38. Use according to claim 37 wherein the anti-parasitic protein is a cysteine protease inhibitor from maize or rice. 39. Use according to any of claims 32 to 38 wherein the transgenic plant is a dietary crop for the host animal. 40. A transgenic plant transformed with DNA encoding an anti-parasitic protein against an animal parasite in a form capable of expressing the protein within the transgenic plant wherein the anti-parasitic protein is a cysteine protease inhibitor from maize or rice and the plant is a dietary crop for the host animal.

Inventors: ATKINSON HOWARD JOHN, KORITSAS VAS MICHAEL, LEE DONALD LEWIS, MACGREGOR ANDREW NEILSON, SMITH JUDITH ELIZABETH, ATKINSON, HOWARD, JOHN, KORITSAS, VAS, MICHAEL, LEE, DONALD, LEWIS, MACGREGOR, ANDREW, NEILSON, SMITH, JUDITH, ELIZABETH
Applicants: ATKINSON HOWARD JOHN, KORITSAS VAS MICHAEL, LEE DONALD LEWIS, MACGREGOR ANDREW NEILSON, SMITH JUDITH ELIZABETH, UNIV LEEDS, ATKINSON, HOWARD, JOHN, KORITSAS, VAS, MICHAEL, LEE, DONALD, LEWIS, MACGREGOR, ANDREW, NEILSON, SMITH, JUDITH, ELIZABETH, THE UNIVERSITY OF LEEDS
Application year: 1995
Main classification: C12N15
IPC codes: A01N65, A61K38, A61P33, C07K14, C12N15