Progress in Control Measures for Chicken Coccidiosis

Kitandu A. , R. Juranová: Progress in Control Measures for Chicken Coccidiosis. Acta Vet. Brno 2006, 75: 265-276. For many years, prophylactic use of anticoccidial drugs has been the primary means of controlling chicken coccidiosis in broiler industry and has played a major role in the growth of this industry. Also the use of live vaccines is well established in the control of the disease. Three groups of live vaccines can be distinguished based on the characteristics of the Eimeria species included in the product: vaccines based on live virulent strains, vaccines based on live attenuated strains, vaccines based on live strains that are relatively tolerant to the ionophores, and non-live subunit vaccines. The mounting problem of drug resitance of Eimeria species has prompted major research efforts to seek alternative means of control through increased knowledge of understanding the immunomodulation, natural-product feed additives, advances in live and recombinant vaccines. This article reviews the above mentioned methods in control of chicken coccidiosis. Chickens, anticoccidial drugs, vaccines, immunomodulators, Eimeria, immunity Chicken coccidiosis is an intestinal infection caused by the intracellular protozoan parasite of the genus Eimeria. Seven species have been recognised to infect chickens: Eimeria tenella, Eimeria necatrix, Eimeria acervulina, Eimeria maxima, Eimeria brunetti, Eimeria mitis, and Eimeria praecox. Each species has its own characteristics with respect to preferred site of infection, pathogenicity and immunogenicity. It is the major parasite disease of poultry, with substantial economic burden estimated to cost the industry more than $ 800 million in annual losses worldwide (Wil l iams 1998). These estimates include the costs of prophylactic in-feed medication for broilers and broiler breeders, alternative treatments if medication fails, and losses due to mortality, morbidity, impaired growth rate, temporary reduction of egg production in layers and poor feed conversion of chickens that survive outbreaks. Modern intensive poultry production is largely dependent upon chemoprophylaxis for the control of coccidiosis (Chapman 1999; Allen and Fet terer 2002), although there is a rising problem of drug resistant strains of Eimeria. In addition the use of live vaccines for control of coccidiosis is also well established (Wil l iams 2002). The life cycle of Eimeria comprises intracellular, extracellular, asexual and sexual stages, so it is not surprising that host immunity is also complex and involves many facets of nonspecific and specific immunity (cellular and humoral immune mechanism) (Li l lehoj 1998), and their pathogenicity varies in birds of different genetic background. Therefore, in the natural host, the immunity is species specific (e.g. chickens immune to one species of Eimeria are susceptible to others). Additionally, Eimeria species exhibit different tissue and organ specificity in the infected host, so, understanding the interplay between the host and the parasites in the intestine is crucial for the design of novel control approaches agaist coccidiosis (Dal loul and Li l lehoj 2005). The introduction of alternative prevention ACTA VET. BRNO 2006, 75: 265–276 Address for correspondence: Dr. Amos Kitandu P.O. Box 7238 Dar-Es-Salaam Tanzania E-mail: drkitandu4@yahoo.com http://www.vfu. cz/acta-vet/actavet.htm measures such as non-chemical feed supplements that effectively enhance productivity and non-specific immunity may help to limit the use of anticoccidials in control of chicken coccidiosis. Control using anticoccidial drugs The effective use of anticoccidial drugs over the past 50 years has played a major role in the growth of poultry industry and has allowed the increased availability of high quality, affordable poultry products to the consumer. Numerous products were introduced, many of which are available and used today. However, there is increasing concern about rising levels of drug resistance (Chapman 1997). The anticoccidial drugs can be classified as 1) Synthetic drugs (chemicals), 2) Polyether ionophores. Synthetic drugs have specific modes of action against parasite metabolism, sulphamides and related drugs compete for the incorporation of paraminobenzoic acid (PABA) and metabolic of folic acid, amprolium compete for absorption of thiamine by the parasite. Quinoxaline and clopidol inhibit energy metabolism in the cytochrome system of coccidia. The quinolones and ionophores arrest or kill the sporozoite or early trophozoite, nicarbazin, robenidine and zoalene destroy the first or second generation schizonts and the sulphonamides act on the developing schizonts and also on the sexual stages. The ionophores kill coccidia by interfering with the balance of important ions such as sodium and potassium. The host cells are able to manage these ions in the presence of ionophores, but the parasites cannot. 1. Synthetic drugs: These drugs were introduced first, then the ionophores followed and are now an important component of coccidiosis control. The recent anticoccidial drugs in control of coccidiosis are diclazuril and toltrazuril (Chapman 1999). The use of toltrazuril as the sole anticoccidial for two consecutive days in the drinking water between days 10 and 14 would be the best time for good coccidiosis control (Mathis et al. 2004). Mehlhorn et al. (1988) reported that toltrazuril is effective against all species of Eimeria infecting chickens. Mehlhorn et al. (1984) also reported that toltrazuril is active against all intracellular developmental stages including those of schizogony and gametogony. It has been reported that despite high efficacy toltrazuril does not intrefere with the development of natural immunity but can even enhance it (Greif 2000). Mathis et al. (2003) demonstrated that toltrazuril was an effective aid to certain anticoccidial program as well as effective as a stand alone anticoccidial. Vanpari js et al. (1989ab, 1990), McDougald et al. (1900ab) reported that diclazuril has a potent, broad-spectrum anticoccidial activity against Eimeria species and it was noted to be highly effective against the six major pathogenic species of Eimeria (Eimeria acervulina, E. maxima, E. tenella E. brunetti, E. necatrix and E. mitis). Chapman et al. (2004) reported that roxarsone has important anticoccidial activity particularly against E. tenella and works very well in combination with ionophores. Also combinations of anticoccidials such as salinomycin and roxarsone with a digestive enhancer such as bacitracin are widely used in the starter and grower feeds of broilers for control of coccidiosis and improvement of growth in broilers (Chapman and Johnson 2002). It is quite clear that some degree of resistance to all anticoccidial drugs, including ionophores, has developed (Chapman 1997). To minimize the effects of resistance, poultry producers rotate the use of various anticoccidials with successive flocks, where drugs from different classes are used sequentlly on a single crop of birds, one class might be used in starter feed, another in growers, returning to the first for the finisher diet, followed by a withdrawal diet (Sangster 2001). 2. Polyether ionophores: Since 1971 the preferred drugs for coccodiosis prevention have been ionophore antibiotics. These drugs still achieve sufficient control despite resistance being common; for example, salinomycin, narasin, monensin, lasalocid, maduramicin and semduramicin remain useful agents except in situation of heavy parasite challenge 266