bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations on the feeding behaviour of parasitic third-stage hookworm larvae
Authors: Hawdon J. M. , Volk S. W. , Rose R. , Pritchard D. I. , Behnke J. M. , Schad G. A.
Published: June 2009

The feeding behaviour of parasitic 3rd-stage larvae (L3) of the hookworms Ancylostoma caninum, A. ceylanicum and Necator americanus was examined. Less than 11% of A. caninum L3 recovered from the small intestines of dogs infected orally were feeding at 4–48 h post-infection (p.i.). and none of the A. ceylanicum L3 recovered from the intestines of orally infected hamsters had resumed feeding. All L4 of both species recovered at 36 and 48 h p.i. had resumed feeding. On the other hand, approximately 16% of the A. ceylanicum L3 recovered from the skin of percutaneously infected hamsters at 18 h were feeding, and the percentage feeding increased to nearly 58% at 44 h p.i. Necator americanus L3 recovered from the skin of percutaneously infected neonatal hamsters resumed feeding at 6–12 h p.i. and reached 90–94% by 18 h. Feeding began to decline at 66 h, and reached 29% at 120 h p.i. This decrease was associated with the migration of larvae from the skin to the lungs. By 192 h p.i. over 95% of the larvae had reached the small intestine, and all had moulted to the L4. The results indicate that parasitic L3 resume feeding in the skin during percutaneous infections, and suggest that feeding by hookworm L3 correlates with the resumption of development.
Stereological estimation of the total number of neurons in the asexually dividing tetrathyridium of Mesocestoides corti
Authors: Yaegashi H. , Howard C.V. , McKerr G. , Burns A.
Published: June 2009

Fifty tetrathyridia of Mesocestoides corti showing various degrees of scolex fission during asexual multiplication were subjected to estimation of the total number of neurons in the central ganglia, using a ‘fractionator’ designed sampling scheme on every 10th Historesin section through the specimen. Neurons were stained with Cresyl fast violet and viewed by transmission light microscopy. Cells were only counted if a nucleolus was present. The animals were divided into groups according to their stage in the asexual reproduction process indicated by head shape and sucker number. Animals which had a narrow head with 4 suckers contained about 250 neurons. As their heads became wider, in preparation for fission, neurons were overproduced by up to 5-fold. As additional suckers were developed (8 in total), neurons were reduced to about 500. Finally, when the animals had 2 clearly discernible heads, with 4 suckers on each, the total number of neurons (per head) was again approximately 250. As the heads became wider again, neuron over-production recommenced. Exceptionally shaped animals with an X- or T-shaped single head were observed. These results suggest that there is a preparatory stage for neuronal regeneration, during which the basic population of neurons is about 250. This is followed by neuron over-production followed by a selective cell death of neurons which occurred during asexual multiplication. Another cycle for neuronal regeneration can occur before an animal completes its fission process.
Role of reactive oxygen species in expulsion ofNippostrongylus brasiliensisfrom rats
Authors: Batra S. , Srivastrava J. K. , Gupta S. , Katiyar J. C. , Srivastava V. M. L.
Published: June 2009

To understand the mechanism for the expulsion ofNippostrongylus brasiliensisfrom rats, age-dependent variations in the metabolism of reactive oxygen species in the parasite and the host intestines were examined.N. brasiliensisshowed an age-dependent increase in its susceptibility to xanthine-xanthine oxidase andt−butyl hydroperoxide generated oxidants as well as to H2O2. Protection obtained with several scavengers suggested that the worms were damaged by the combined action of oxidants generated by thein vitrosystems employed. The level of superoxide dismutase in the nematode and its release into the surroundings exhibited a marked depression with advancement of age. No such alteration was, however, recorded for catalase and glutathione peroxidase. An appreciable decrease in the level of reduced glutathione in olderN. brasiliensisappears to render them prone to oxidant attack. The rat intestines, on the other hand, exhibited an appreciable depression in catalase and a reduced glutathione content with progress of the infection. Vitamin E levels were elevated. The release of O27and H2O2by the intestines was also found to be greater during later stages of the infection. The combined effect of the changes observed inN. brasiliensisand in the rat intestines may be at least partly responsible for expulsion of the nematode from the rats after day 10.
Preliminary analysis of the transmission dynamics of Theileria parva in eastern Africa
Authors: Medley G. F. , Perry B. D. , Young A. S.
Published: June 2009

Two mathematical models are developed that investigate the transmission dynamics of Theileria parva by the ixodid tickRhipicephalus appendiculatus to cattle in endemically stable areas. A method of estimating the rate of infection to cattle ofT. parva at the endemically stable state is given. Empirical estimates of ail the parameters in the model are available. The degree to which animals that have recovered from theileriosis (the ‘carrier’ state) are able to transmit the infection to tick nymphs or larvae is a crucial determinant of the dynamics of infection in a herd. Two control methods influencing the transmission of infection are considered – infection and treatment immunization and the reduction in tick feeding by acaricide application. The impact of each method on the transmission of infection is evaluated. Future developments and the data required to predict the dynamics of T. parva infections in cattle and ticks are discussed.
An IgG (Fcγ,)-binding protein ofTaenia crassiceps(Cestoda) exhibits sequence homology and antigenic similarity with schistosome paramyosin
Authors: Kalinna B. , McManus D. P.
Published: June 2009

Previous studies from this laboratory have suggested the presence of antibody-binding molecules on the surface ofTaenia crassicepsmetacestodes. We now report the purification of aT. crassicepsFcγ-binding protein which has an equivalent molecular size (96 kDa), is antigenically similar and exhibits significant amino acid sequence homology to schistosome paramyosin. The similarities in molecular weight of theT. crassicepsprotein,Schistosoma mansoniparamyosin and antigen B ofT. solium, the close amino acid sequence homologies between theT. crassicepsprotein andS. mansoniparamyosin and betweenS. mansoniparamyosin and antigen B ofT. solium, and the antigenic similarity of theT. crassicepsprotein with paramyosin indicates that this family of platyhelminth proteins are closely related. The known characteristics ofT. soliumantigen B (collagen binding affinity; disruption of complement function) and the Fcγ-binding activity of theT. crassicepsmolecule suggests that this class of proteins may be multifunctional, fulfilling not only a structural role but also as components interacting with the host immune system to increase parasite survival.
Hookworm infections and human iron metabolism
Authors: Crompton D. W. T. , Whitehead R. R.
Published: June 2009

Ancylostoma duodenale and Necator americanus are extremely common species of soil-transmitted helminth which flourish where poverty and malnutrition prevail. Hookworms contribute significantly to iron-deficiency anaemia, which remains one of the world's major nutritional problems, through the feeding activities of intestinal stages leading to chronic blood loss into the gut. In this article, a mathematical model is proposed to explain how human iron metabolism may respond to hookworm infection of varying intensity. The model draws attention to the importance of the regulation of stored iron levels in the process. The results from the model are presented for the effects of hookworm infection on the iron metabolism of a healthy adult male. Calculations are also presented in which the effects of hookworms on the iron metabolism of a non-pregnant woman are compared with those of a pregnant woman. Use of the model may help develop a better understanding of the pathology of hookworm disease.
Infection, nutrition and cognitive performance in children
Authors: Connolly K. J. , Kvalsvig J. D.
Published: June 2009

The paper considers briefly the nature of cognition and its relationship to intelligence. The information processing model of human cognition is outlined and IQ and DQ are explained. The literature dealing with the effects of malnutrition and parasitic infection on cognitive performance and development in children is selectively reviewed. A speculative hypothesis concerning the psychological effects of parasitic infection is sketched and brief consideration is given to models and measures in research on development.
Models of intermediate complexity in insect-pathogen interactions: population dynamics of the microsporidian pathogen,Nosema pyrausta, of the European corn borer,Ostrinia nubilalis
Authors: Briggs C. J. , Godfray H. C. J.
Published: June 2009

Nosema pyraustais an important microsporidian pathogen of the European corn-borer,Ostrinia nubilalis(Pyralidae), a major pest of corn (maize). The population dynamics of the interaction between the moth and its pathogen have been studied previously using simple models phrased as coupled differential equations, and using large simulation models containing over 150000 coupled equations. A middle approach is adopted here and the interaction studied using an age-structured model written as a system of delay-differential equations. Although the model contains twenty four parameters, estimates for twenty of these were available in the literature. Our model provides a good qualitative match to observed within and between season dynamics and suggests which aspects of the interaction are most important in determining the nature of the system's population dynamics. More generally, we argue that in the absence of better data on insect-disease interactions in natural habitats, valuable insights can be gained by studying equivalent systems in agro-ecosystems. We also argue that models of intermediate complexity that incorporate considerable detail about the natural history of individual interactions, but which are derived from the classical models of animal ecology and epidemiology, offer the most profitable way of modelling insect-pathogen interactions in the wild.
Serotonin and its requirement for maintenance of contractility in muscle fibres isolated fromSchistosoma mansoni
Authors: Day T. A. , Bennett J. L. , Pax R. A.
Published: June 2009

Muscle fibres isolated from adultSchistosoma mansonicontracted in a dose-dependent manner when exposed to elevated K+with a maximum response obtained with 25 mM K+. These contractions were dependent on extracellular Ca2+since Co2+(5 mM) or nicardipine (1 μM) blocked the high K+contractions. Serotonin (300 nM or higher) was required for maintenance of high K+contractions. With concentrations of serotonin less than 300 nM the response was dose dependent. 5-Methoxytryptamine or α-methylserotonin at 1 μM as well as 10 μM tryptamine were able to substitute for serotonin, but 1 μM 5-carboxyamidotryptamine was ineffective. The order of potency for antagonists (10 μM) was: methiothepin > metergoline > Ly-278,584 = ketanserin. This pattern of responsiveness does not fit well with any known mammalian serotonin receptor subtype. Since forskolin, an adenylate cyclase activator, is able to mimic the action of serotonin and H89, a protein kinase inhibitor, is able to block the effect of serotonin, the effect of serotonin on contractility of the muscle may beviaa cAMP-dependent pathway.
Characterization of three neutral proteases ofSpirometra mansoniplerocercoid
Authors: Kong Y. , Chung Y.-B. , Cho S.-Y. , Choi S.-H. , Kang S.-Y.
Published: June 2009

In the pathogenesis of sparganosis, proteases have been considered to play important roles in tissue migration and parasite feeding. Several bands of proteolysis were observed when crude extracts ofSpirometra mansoniplerocercoid (sparganum) were examined using gelatin substrate gel at neutral pH, of which two proteases of 198 and 104 kDa were purified by two chromatographic steps, and a 36 kDa protease was purified by gelatin-affinity and DEAE–anion exchange chromatography. All the purified proteases exhibited optimal activity at pH 7·5 and 0·1 M Tris–HCI. Proteolytic activities at 198 and 104 kDa were inhibited specifically by serine protease inhibitors, and 4-(amidinophenyl)methansulfonyl fluoride (APMSF, 0·5 m) andN-α–p–tosyl-L-lysine chloromethyl ketone (TLCK, 1 mM), which strongly suggested that these two proteases were trypsin-like proteases. The activity of the 36 kDa protease was inhibited byN-tosyl-l-phenylalanine chloromethyl ketone (TPCK, I mM) and chymostatin (0·1 mM), and was potentiated in 10 mM Ca2+which showed that the protease had a chymotrypsin-like property. All the proteases were Schiff(PAS) positive. Proteases of 198 and 104 kDa degraded collagen completely within 24 h. The 36 kDa enzyme cleaved human recombinant interferon-γ (rIFNγ) and bovine myelin basic protein. In addition, all the purified proteins elicited strong antibody responses in the infected patients.
Tsetse–trypanosomiasis challenge to village N'Dama cattle in The Gambia: field assessments of spatial and temporal patterns of tsetse–cattle contact and the risk of trypanosomiasis infection
Authors: Wacher T. J. , Milligan P. J. M. , Rawlings P. , Snow W. F.
Published: June 2009

The severity of the trypanosomiasis problem in a particular location is traditionally assessed in terms of a challenge index – the product of some measure of tsetse abundance and infection rate – which is assumed to be proportional to the force of infection. However, this index masks variation in the force of infection between herds and among individuals within herds. It is also not comparable between sites since the relative abundance of tsetse to hosts may vary. We have studied spatial distribution of herds of cattle in relation to tsetse in The Gambia and calculated an index of challenge based on the ratio of vectors to hosts over the livestock ranging area. This index is strongly correlated with estimates of the force of infection calculated from the incidence of infection in susceptible zebu; and it provides information on heterogeneity in exposure of different herds to tsetse.
Regional versus local helminth parasite richness in British freshwater fish: saturated or unsaturated parasite communities?
Authors: Kennedy C. R. , Guégan J.-F.
Published: June 2009

The relationships between regional species richness and local species richness were examined in respect of helminth parasite communities in 32 species of freshwater fish in the British Isles. Fish were divided into 5 categories, for each of which the goodness of fit of the relationship to linear, exponential and power function models was tested. For all categories of fish combined, there was a significant, positive curvilinear relationship. Nested within this were two other patterns. For introduced fish, a linear model provided the best fit; for euryhaline and relict species it was impossible to determine the best model, but for the other categories the relationship was curvilinear and was best fitted by a power function model. The linear relationship found for introduced fish was interpreted as a temporary situation, reflecting the shortage of time for the communities to become saturated. It corresponded to the linear part of the curvilinear relationship of the other categories, which is believed to represent the fundamental form of the relationship for parasite communities. The communities reached a saturation level of richness, corresponding to the asymptote of the curve, which fell well below regional species richness. Explanations for local saturation are discussed, but neither community structure nor supply-side ecology can yet be preferred. It is concluded that local patterns in helminth community richness, in contrast to those in fish assemblages, are not significantly influenced by patterns on a larger, regional spatial scale and so regional species richness is not a key determinant of local species richness, nor does a knowledge of regional patterns improve predictability of local patterns.
Immunocytochemical localization of serotonin (5-HT) in the nervous system of the hydatid organism, Echinococcus granulosus (Cestoda, Cyclophyllidea)
Authors: Brownlee D. J. A. , Fairweather I. , Johnston C. F. , Rogan M. T.
Published: June 2009

The localization and distribution of the serotoninergic components of the nervous system in the hydatid organism, Echinococcus granulosus, were determined by immunocytochemical techniques in conjunction with confocal scanning laser microscopy (CSLM). The distribution of serotonin immunoreactivity (IR) paralleled that previously described for cholinesterase activity, although it was more widespread. Nerve cell bodies and nerve fibres immunoreactive for 5-HT were present throughout the central nervous system (CNS), occurring in the paired lateral, posterior lateral and rostellar ganglia, their connecting commissures and nerve rings in the scolex and in the ten longitudinal nerve cords that run posteriorly throughout the body of the worm. A large population of nerve cell bodies was associated with the lateral nerve cords. In the peripheral nervous system (PNS), immunoreactive nerve fibres occurred in well-developed nerve plexuses innervating the somatic musculature and the musculature of the rostellum and suckers. The genital atrium and associated reproductive ducts were richly innervated with serotoninergic nerve cell bodies and nerve fibres.
Studies on the nutrient uptake by the beet cyst nematodeHeterodera schachtiibyin situmicroinjection of fluorescent probes into the feeding structures inArabidopsis thaliana
Authors: Böckenhoff A. , Grundler F. M. W.
Published: June 2009

A method was developed, which enables substances to be injected into the feeding structure (syncytium) established byHeterodera schachtiiin roots ofArabidopsis thaliana. The technique was used to study the uptake of nutrients by the feeding nematode. The fluorescent dye lucifer yellow CH (LYCH) and fluorescence-labelled dextrans of different molecular weights were injected into the thin and translucent roots ofA. thaliana. Such roots are a feature of this plant and they provide optimal conditions for microinjection. Injected LYCH was taken up by feeding juveniles and adults, indicated by the staining of the alimentary duct and the digestive system. Fluorescent dextrans of 3, 10 and 20 kDa but not of 40 and 70 kDa were ingested, suggesting that molecules of a maximum Stokes radius of 3·2 to 4·4 nm are taken up. It is likely that the feeding tube, forming the interface between the plant cytosol and the nematode's digestive system, is responsible for this size exclusion effect. The injected fluorescent substances were not detected in plant cells adjacent to the syncytium or in the root vascular elements. Injections into parts of roots which were infested by several nematodes revealed that feedingH. schachtiiindividuals may share one syncytium.
Superoxide dismutase (SOD) activity ofDictyocaulus viviparusand its inhibition by antibody from infected and vaccinated bovine hosts
Authors: Britton C. , Knox D. P. , Kennedy M. W.
Published: June 2009

The presence of superoxide dismutase (SOD) activity in the bovine lungwormDictyocaulus viviparuswas examined using the xanthine–xanthine oxidase assay system and by non-denaturing PAGE followed by specific enzyme staining. High levels of activity were detected in excretory–secretory (ES) products of adult worms and in soluble extracts of both the L3 and adult stages of the parasite. Stage-specific and ES-specific activities were indicated by differences in SOD isoenzyme profiles between adult and larval parasite extracts and between adult extract and ES products, with a fast migrating activity being specific to ES products. All isoenzymes were sensitive to cyanide, indicating copper/zinc dependency. The antigenicity of ES SOD was demonstrated by a reduction in SOD activity in both the chemical assay and non-denaturing PAGE following incubation of parasite ES products with IgG antibody purified from serum of infected or vaccinated bovine hosts. The high level of SOD activity released by adultD. viviparusmay be a reflection of the problems faced by a parasite occupying an oxygen-rich environment. Antibody inhibition of SOD may, therefore, be an important target of protective immunity.
Immunogenicity of a hybridPlasmodium falciparum, malaria antigen
Authors: Lockyer M. J. , Cooper H. , Tite J. , Rowan W. , Crowe J. S.
Published: June 2009

A recombinant baculovirus-expressed hybrid protein containing epitopes for the C-terminal fragment of thePlasmodium falciparumprecursor to the major merozoite surface antigens (PMMSA) and the tetrapeptide repeats of the circumsporozoite protein (CSP) was assessed for its immunogenicity. Murine MHC-II restriction of the antibody response to the CSP repeats was not overcome by the PMMSA component, the response to which showed no restriction. In an adjuvant trial the highest antibody titres in rabbits to both components of the hybrid were obtained using Freund's adjuvant. Lack of a boosting antibody response to the CSP repeats appeared to be linked to the conformation of the PMMSA component. Formulation of the hybrid protein into Iscoms gave antibody titres of only short duration to both components.
Population dynamics ofTheileria sergentiin persistently infected cattle and vector ticks analysed by a polymerase chain reaction
Authors: Kubota S. , Sugimoto C. , Onuma M.
Published: June 2009

Theileria sergentiShintoku stock consists of 2 parasite populations bearing 2 atlelic forms of p33/32, an immunodominant piroplasm surface protein. Parasite population changes during parasite passages among cattle and tick vectors, and during persistent infection in individual calves were analysed by using allele-specific polymerase chain reaction (PCR). The parasite DNAs were prepared from piroplasms from calves which had been infected with Shintoku stock by inoculation of sporozoite stabilates or parasitized erythrocytes, and from sporozoite stabilates which had been prepared from Shintoku stock-infected ticks. Changes in a dominant parasite population were demonstrated during transmission from calves to vector ticks and from infected ticks to calves. Parasite population changes were also apparent during persistent infection in cattle over several months, and this change is thought to occur under host immune pressure. The results of this study indicate that expression of diverse forms of p33/32 may play a role in parasite persistence within mammalian hosts and its transmission from tick vector.
Trypanosoma brucei s.1.: evolution, linkage and the clonality debate
Authors: Stevens J. R. , Tibayrenc M.
Published: June 2009

The Index of Association (IA) has been proposed by Maynard Smith et al. (1993) as a general method for characterizing the population structures of microorganisms as either: clonal, epidemic, cryptic species or panmictic. With reference to the current debate surrounding the mode of reproduction in parasitic protozoa, this study explores (i) the suitability and limitations of the IA for characterizing populations of Trypanosoma brucei s.l., and (ii) the idea that the significance of genetic differences between populations may be better understood if the evolution, spread and temporal stability of certain parasite genotypes are also considered. Four populations of T. brucei from Côte d'Ivoire, Uganda and Zambia are analysed using the IA and a complementary test for linkage disequilibrium, test f of Tibayrenc, Kjellberg & Ayala (1990). The two populations from Uganda are characterized as epidemic, while the others appear more or less clonal; the merits of the two methods are compared. The implications of the various population classifications are discussed with reference to genotype longevity in each region; the evolutionary and biomedical consequences of the genetic non-homogeneity of T. brucei are reviewed.
The excystment, growth and reproduction of Acanthoparyphiutn spinulosum Johnston, 1917 (Trematoda) in chicks fed various diets
Authors: Little John W.
Published: June 2009

Studies have been made of the growth and excystment of a trematode, Acanthoparyphium spinulosum, in chicks fed on various denned diets.

Day-old chicks were fed metacercariae and maintained on deficient as well as complete rations for periods up to 20 days. The excystment rate was determined by the number of worms that were recovered from the metacercariae. The largest number of worms were recovered from chicks that received a normal diet with starch as the sole carbohydrate source. The smallest percentage of parasites was found in birds that had received a normal diet with sucrose serving as the carbohydrate source. About 25 % were recovered from chicks fed several other diets.

The trematodes developed and grew well in vitamin A deficient chicks; there was a large number of intra-uterine ova observed in worms from these hosts. Acanthoparyphium spinulosum from chicks fed a ‘no vitamin D’ diet grew at a normal rate until the 6th day; after this they grew more slowly than 6-day-old worms in chicks fed the ‘no vitamin A’ diet.

The lengths of worms from birds deprived of all vitamins differed little from those of the parasites recovered from the chicks deficient in vitamin D. The largest worms were obtained from chicks fed a complete diet with starch as the sole carbohydrate source.

Parasites from chicks fed a diet 50 % deficient in carbohydrates (with sucrose as the carbohydrate) developed normally.

Worms also developed in chicks fed a ‘no protein’ diet with starch and a ‘no protein’ diet with sucrose. A deleterious effect on ova production was observed in worms from both these groups.

Metacercariae developed in chicks fed a ‘no carbohydrate’ diet, but no mature worms were recovered due to the reduced life of the host. Starvation of the hosts produced small worms containing few intra-uterine ova.

The growth curve of A.spinulosum was plotted and compared with Echino-paryphium flexum.

This investigation was supported in part by U.S. Public Health Service Grant UI-00202, and by a grant-in-aid of research by the Society of the Sigma Xi, New Haven, Connecticut.
Studies on the structure and hatching of the eggs of Schistosoma mansoni
Authors: Kusel J. R.
Published: June 2009

The structure and function of the vacuoles in the eggs of Schistosoma mansoni is unknown. In this study the eggs have been immersed in serum albumin and examined by phase-contrast optics. Under these conditions the vacuoles exhibit a definite internal structure, suggesting that they may be or may have been cellular. Histochemical staining techniques to detect the nature of the vacuolar contents revealed that the vacuoles stained heavily with iodine and gave a positive PAS reaction. This suggested the presence of carbohydrate. Stains for nucleic acids, protein and lipid were not taken up by the vacuoles. The egg shell stained with o–toluidine blue and with basic fuchsin uniformly, except for a thin irregular band which might indicate a possible line of weakness. The vacuolar membranes seem to be similar to the vitelline membrane in permeability to hydroxyl ions and it is possible that these membranes have a common origin. Plasmolysis studies with salts, urea, glycerol and sucrose showed that the vacuolar membranes have about the same permeability properties to these compounds as the other egg membranes. Glycerol treatment of the eggs until equilibrium is attained, followed by transfer of the eggs to water or saline results in a hatching of the eggs. In this, a dead mira-cidium is extruded from the shell. Similar treatment of eggs equilibrated with sucrose does not result in this hatching process. It is postulated that glycerol solubilizes a factor which aids the hatching process.

I should like to thank the following: Dr S. A. Ibrahim, in whose department this work was carried out; Dr S. Dawood of the Stack Laboratory, Khartoum, who kindly made his microscope available for use; Mr J. R. Lauder for valuable discussions and suggestions; and many young patients in Khartoum Civil Hospital for stool samples and smiles.
Action of pyrimethamine and related drugs againstPlasmodium knowlesi in vitro
Authors: Gutteridge W. E. , Trigg P. I.
Published: June 2009

A dihydrofolate reductase has been isolated from free-parasite preparations of the primate malarial parasite,Plasmodium knowlesi. Its properties are similar to those reported for the enzyme from the rodent malarial parasite,P. berghei,even though the base compositions of the DNA of these two species are quite different. TheKmsfor substrate and cofactor are 3 × 10−6Mand 1 × 10−6Mrespectively and the molecular weight is ˜ 200000. Concentrations of pyrimethamine and trimethoprim as low as 1 × 10−9Mand 3 × 10−8Mrespectively are sufficient to cause 50% inhibition of enzyme activity. The sensitivity to inhibition by pyrimethamine and trimethoprim of growth of cultures ofP. knowlesihas also been investigated. Preliminary experiments showed that it was only the schizont stage that was susceptible to the action of the drugs and that in their presence, normal nuclear divisions and segmentation did not occur and subsequently, no reinvasion of fresh red cells took place. The minimum concentrations of drug required to produce these effects were 10−9Mfor pyrimethamine and 10−7Mfor trimethoprim. Thus, there is a close correlation between the concentrations of pyrimethamine and trimethoprim required to inhibit the dihydrofolate reductase in a cell-free system and the growth of the parasitein vitro. Pyrimethamine (10−9M) did not, however, affect the incorporation of radioactive precursors into DNA, RNA or protein of schizont stage parasites until after morphological damage could be seen and reinvasion was complete in control cultures. The time courses of incorporation of [14C]algal protein hydrolysate into protein in the presence (10−9M) or absence of pyrimethamine are the same as those described recently with immune serum. The possibility is thus raised as to whether pyrimethamine and immune serum act in the same way.

One of us (P.I.T.) received financial assistance from the World Health Organization. We thank Dr F. Hawking for many helpful discussions, Miss Jane Dunnett and Mr T. Scott-Finnigan for technical assistance and Dr O. D. Standen for samples of pyrimethamine and trimethoprim.
Physiology and pharmacology of turbellarian neuromuscular systems
Authors: Blair K. L. , Anderson P. A. V.
Published: June 2009

Our understanding of the neurobiology of the Platyhelminthes has come in large part from free-living turbellarians. In addition to providing considerable information about the capabilities of the rudimentary nervous system present in all members of the phylum, turbellarians have provided the most definitive information about the variety of ion channels present in the membranes of neurones and muscle cells, and about the physiology and pharmacology of those channels. Furthermore, preparations of single, viable muscle cells have provided some of the most conclusive evidence about the variety of transmitters present, and the types of response they evoke. Here, we review what is known about the physiology and pharmacology of the turbellarian neuromuscular system. Particular attention is given to the triclad flatwormBdelloura Candida, the best studied species in this respect, but other species are included where relevant.
Neuromuscular physiology and pharmacology of parasitic flatworms
Authors: Pax R. A. , Day T. A. , Miller C. L. , Bennett J. L.
Published: June 2009

The trematode and cestode flatworms include numerous parasitic forms of major medical and economic importance. A better knowledge of the neuromuscular physiology of these animals could lead to development of new control measures against these parasites. Since these animals are near the stem from which all other animals have evolved, better knowledge of these animals could also yield valuable information about the early evolution of nerve and muscle systems in the animal kingdom. This review focuses on what is known about the characteristics of the somatic muscle in these animals. The anatomy of the muscles is described along with a review of current information about their electrophysiology, including descriptions of the ion channels present. Also included is a summary of recently acquired data concerning the nature of serotonin, peptide, acetylcholine and glutamate receptors on the membranes of the muscles.
The motornervous system ofAscaris: electrophysiology and anatomy of the neurons and their control by neuromodulators
Authors: Davis R. E. , Stretton A. O. W.
Published: June 2009

Analysis of the electrical properties of neurons in the motornervous system of Ascaris suum suggests that it is largely an analogue system. The motorneurons do not conduct action potentials and they release transmitter tonically at their normal resting potential; transmitter release is increased or decreased as a continuous function of membrane potential. Despite extensive physiological descriptions of the electrical properties of the neurons and their synapses, as well as morphological descriptions of the synaptic circuitry of the system, the predicted activities of the neurons in the circuit differ from those observed by direct recording in semi-intact behaving animals. We conclude that the description of the circuit is incomplete. There are several possibilities for the missing elements, including chemical, proprioceptive, and additional neuronal components. Recently, attention has been focussed most heavily on the intercellular chemical signalling systems; in addition to those mediated by classical neurotransmitters, a surprisingly complex array of neuropeptides has been identified. One family of these peptides, the AF peptides, has been analyzed in detail. It comprises at least 20 peptides, and they fall into sequence-related subfamilies. One of these subfamilies, containing 6 peptides, is encoded by a single transcript, suggesting that the AF peptides are under multiple genetic control. All AF peptides tested have potent activity on the motornervous system and or on muscle. There are multiple physiological activities, and cellular localization studies show multiple patterns of cellular expression. Studies on Panagrellus and Caenorhabditis emphasize the diversity of this family and its genetic control.
Pharmacology of anthelmintic resistance
Authors: Sangster N.
Published: June 2009

Anthelmintic resistance has compromised the control of nematode parasites in several animal-based industries. Studies of resistance have not only improved our understanding of this phenomenon but also shed light on physiological systems of parasitic helminths. In addition, research on molecular aspects of anthelmintic resistance may provide selectable markers for use in future transfection studies with helminths. Several anthelmintics act on helminth neuromuscular systems. Drugs such as levamisole are cholinergic agonists and, based on pharmacological studies, levamisole-resistant nematodes appear to have altered acetylcholine receptors. It is likely that anticholinesterase anthelmintics share cross resistance with levamisole. Ivermectin appears to be a glutamate agonist.In vitrostudies of ivermectin-resistant nematodes suggest that IVM receptors are located on pharyngeal and somatic muscle. The free-living nematodeCaenorhabditis elegansmay provide a model for anthelmintic resistance. It has been useful in cloning drug receptors from parasites but differences between its life history and habitat compared with parasitic nematodes may limit its usefulness for studying resistance in these parasites.
Prospects for rational approaches to anthelmintic discovery
Authors: Thompson D. P. , Klein R. D. , Geary T. G.
Published: June 2009

Rational approaches to anthelmintic discovery include the design of screens for compounds directed at specific proteins in helminths that are pharmacologically distinguishable from their vertebrate homologues. The existence of several anthelmintics that selectively target the neuromusculature of helminths (e.g. levamisole, ivermectin, praziquantel, metrifonate), together with recent basic research in helminth physiology, have contributed to the recognition that neurobiology distinguishes these organisms from their vertebrate hosts. In this survey, we focus on mechanism-based screening and its application to anthelmintic discovery, with particular emphasis on targets in the neuromusculature of helminths. Few of these proteins have been exploited in chemotherapy. However, recent studies in comparative pharmacology and molecular biology, including theC. elegansgenome project, have provided insights on potential new targets and, in some cases, molecular probes useful for their incorporation in mechanism-based screens.
The oncomiracidium and post-oncomiracidial development of the hexabothriid monogeneanRajonchocotyle emarginata
Authors: Wiskin Maureen
Published: June 2009

A description is given of some features of the embryonic development, the structure of the oncomiracidium and the postlarval development ofR. emarginata, a hexabothriid parasite on the gills ofRaia clavata.

There are three phases in the larval development of the haptor ofRajonchocotyle:an oncomiracidial or marginal hook stage, a hamulus stage and a sucker stage. Neither the embryo nor the oncomiracidium ever possesses more than five pairs of marginal hooks and marginal hooks I (the posterior-most pair) are considered to be missing. The marginal hooks develop within distinct binucleate oncoblasts. During the early stages of post-oncomiracidial growth the secondary attachment organs of the haptor are formed and it is only after the completion of the development of the haptor that the reproductive organs begin to appear. Firstly, a pair of hamuli is acquired, followed by four pairs of suckers, which form in posterior-anterior succession at the site of marginal hooks III-VI. The first pair of suckers remains unarmed while the other three pairs acquire hooked sclerites and become the main functional attachment organs of the adult. As the first pair of suckers appears the posterior part of the haptor lengthens to form a caudal appendage. Hexabothriids are considered to show closer affinity to the 8-suckered chimaericolids and diclidophorids than to the 6-suckered polysto-matids, the unarmed suckers representing a simplification, by loss of the sclerite and reduction in sucker size, of an originally armed sucker.

I would like to express my thanks to Dr J. Llewellyn for his interest and for much helpful discussion.

Thanks are also due to the Director and Staff of the Marine Biological Association at Plymouth, in particular Mr J. E. Green for material and assistance, and to Dr A.j Brinkmann, of the Department of Zoology, University of Bergen, for supplying specimens ofSqualonchocotyle borealis.
Codon usage and bias among individual genes of the coccidia and piroplasms
Authors: Ellis J. T. , Morrison D. A. , Avery D. , Johnson A. M.
Published: June 2009

Codon usage has been analysed in individual gene sequences, derived from a variety of parasitic protozoa in the class Sporozoa of the phylum Apicomplexa using metric multidimensional scaling. The two groups of codon usage patterns detected reflect the two main subgroups of organisms studied (the coccidia and the piroplasms), and it is the pattern usage of synonymous codons that has the largest influence on overall codon usage in the individual genes, rather than being the pattern of amino acid composition of the gene product. The magnitude of the codon usage bias in the sequences was determined using three commonly used indices – NC', GC3sand B. In general, although relatively low levels of codon usage bias were detected in these gene sequences, codon usage bias does explain at least some of the codon usage patterns observed. Codon usage bias was observed to be dependent on the overall base composition of the genes analysed, which in turn was reflected in the types of codons that were either over-or under-represented in the nucleotide sequences. keeping with observations on prokaryotic organisms, it is speculated that the codon usage patterns detected in these parasitic protozoa are the result of directional mutation pressure on the base composition of the genomic DNA.
The effect of the tetrathyridia of Mesocestoides corti on the livers and peripheral blood of three different strains of mice
Authors: Riley S. L. , Chernin J.
Published: June 2009

Three strains of male and female mice, CFLP, BALB/c and CBA/ca, were infected i.p. with the tetrathyridia of Mesocestoides corti and examined in groups of 5 at 0, 7, 14, 21, 28 and 42 days post-infection. At post-mortem the numbers of parasites both loose in the peritoneal cavity and in the liver tissue were counted, the livers weighed fresh and sections of liver stained to examine the inflammatory response, encapsulation of the tetrathyridia and for eosinophils, neutrophils, mast cells and plasma cells. BALB/c mice had significantly more parasites loose in the peritoneal cavity than CFLP and CBA/ca mice. Infected livers of all three strains were significantly heavier than control livers; the heaviest livers were those of the CFLP followed by the CBA/ca mice which also showed the greatest rate of weight increase. The tetrathyridia from the peritoneal cavities of the CBA/ca and CFLP mice were covered with a ‘mucilage-like’ substance. Tetrathyridia within the host capsules of the CBA/ca mice contained host cells. There was no strain difference with regard to numbers of tetrathyridia in the liver but male mice harboured significantly more parasites than females. Differences in the numbers of cell types within the liver were detected between the strains but no one strain showed any consistent pattern. There was an overall increase in total white blood counts as well as an increase in the number of eosinophils, monocytes, neutrophils and lymphocytes during the course of the infection.
Dynamics of the interaction between the parasitic isopod, Anilocra pomacentri, and the coral reef fish, Chromis nitida
Authors: Adlard R. D. , Lester R. J. G.
Published: June 2009

Field and laboratory investigations into the effect of the parasitic isopod Anilocra pomacentri (Cymothoidae) on the population dynamics of the reef fish Chromis nitida (Pomacentridae) were carried Out at Heron Island, Great Barrier Reef, Australia. Fish carried a single adult parasite just posterior and dorsal to the eye either to the right or to the left of the midline. The adult parasite was overdispersed among fish on patch reefs (dispersion factor, k = 0·69). Sequential field observations on a single cohort of fish showed that parasites significantly depressed growth, reproduction, and survivor-ship. The von Bertalanffy growth coefficients (a measure of somatic growth) were 0·10 for parasitized fish compared with 0·17 for non-parasitized fish. Female fish carrying the parasite produced only 12% of the number of eggs produced by non-parasitized fish of the same size. In the field, the mortality of infected juvenile C. nitida (LCF 15–30 mm) was estimated to be at least 88% in the first 70 days after recruitment of the fish. The mortality of uninfected recruits over the same period was 66%. In laboratory trials, the mortality associated with the infection of juvenile fish by larval parasites ranged from 78% for small fish (mean LCF 15·0 mm) to 28% for larger fish (mean LCF 24·9 mm) within 4 days of experimental infection. This is one of the few studies that evaluates the effect of a parasite on a population of fish in the field.
Characterization of a HMG2-like protein fromSchistosoma mansoni
Authors: Fantappié M. R. , Rumjanek F. D.
Published: June 2009

An HMG2-like protein was purified from nuclear extracts of adultSchistosoma mansoni. Investigation of the amino acid composition of the schistosome HMG2-like protein showed that glutamic acid, glycine, aspartic acid and lysine were the most abundant. Carbohydrate analysis showed that the HMG2-like protein presented a low degree of glycosylation, galactose or glucose being the major monosaccharide constituent. Incubation of live schistosomes with32P followed by isolation of nuclear proteins showed that the HMG-2 like protein could be phosphorylated. Partial sequence analysis of cyanogen bromide peptides revealed the occurrence of a phosphorylation consensus motif. The schistosome HMG2-like protein was found to bind preferentially to single-stranded DNA. The results suggest that the major non-histoneS. mansoninuclear protein belongs to the HMG family.
Molecular systematics in the acanthocephalan genus Echinorhynchus (sensu lato) in northern Europe
Authors: Väinölä R. , Valtonen E. T. , Gibson D. I.
Published: June 2009

New biological species and high levels of inter- and intraspecific genetic divergence were discovered in an allozyme study of some North European members of the acanthocephalan genus Echinorhynchus (sensu lato), parasites of fish and malacostracan crustaceans. (i) A strong differentiation between the marine E. gadi and the fresh- and brackish-water E. salmonis (genetic identity I ≃ 0) supports a generic distinction between these taxa; however, the subdivision would not entirely concur with the concepts of Echinorhynchus (sensu stricto) and Metechinorhynchus suggested earlier. (ii) Samples of E. gadi from the Baltic, Norwegian and North Seas included three distinct, partially sympatric biological species (spp. I–III; I ≃ 0·5). (iii) E. bothniensis, previously only known from the northern Baltic Sea, represents a complex of freshwater taxa with an intermediate host relationship to the ‘glacial relict’ Mysis spp. and with a distributional and host analogy to the North American E. leidyi. A population in a northern lake in the Barents Sea basin is closely related to E. bothniensis of the Baltic area, but is probably specifically distinct; the divergence between these populations (I ≃ 0·6) is similar to that between their Mysis host species. (iv) Considerable intraspecific differentiation (Fst = 0·25), probably reflecting post-glacial population bottlenecks, was found between Baltic and nearby lacustrine E. bothniensis, and between Atlantic and Baltic E. gadi sp. I.
The effects of chloroquine on the infectivity of chloroquine-sensitve and -resisant populations of Plasmodium yoelii nigeriensis to mosquitoes
Authors: Ichimori K. , Curtis C. F. , Targett G. A. T.
Published: June 2009

Subtherapeutic doses of chloroquine have been reported to enhance infectivity of drug-resistant Plasmodium species to their vectors. In this investigation, Plasmodium yoelii nigeriensis N67 strain showed enhanced infectivity to mosquitoes when stimulated by chloroquine. Both sensitive and resistant clones were derived from the N67 strain by dilution, showing that this strain is polymorphic for the resistant trait. A resistant subline was derived by selection under drug pressure from a chloroquine-sensitive clone, but neither the sensitive nor the resistant clones or sublines showed enhancement of infectivity in the presence of chloroquine. This suggests that the enhancement of infectivity shown by the N67 strain is a response to chloroquine stimulation shown only by certain of the genotypes within it, and that this response to chloroquine is not a trait causally connected with the genes coding for chloroquine resistance.