Review on Vaccine Development Against Enteric Parasites Eimeria and Cryptosporidium.

Abstract

Intensive rearing practices have been developed within the past few decades to keep pace with the increasing demand for the high quality, low cost protein source that poultry provides. A major negative consequence of these practices has been an increase in the incidence of diseases. Enteric diseases, in particular, have emerged as a major problem threatening the future viability of the poultry industry. A variety of methods have been used to combat avian diseases in the commercial setting including improved farm management practices, use of antibiotic drugs, selection of disease resistant chicken strains and manipulation of the chicken immune system. In the latter category, development of vaccines against the major avian diseases has become a priority in the poultry industry. Protozoan parasites of the genus Eimeria and Cryptosporidium represent two major parasitic diseases which multiply in the gut of wide range of hosts, including poultry and livestock. Currently, there is no treatment for cryptosporidiosis although chemotherapy is extensively used to control coccidiosis in chickens. However, development of drug resistance by coccidia parasites, the increasing cost of identifying new antibiotic compounds and public awareness of drug residues in foods warrant alternative methods to prevent parasitic diseases. To this end, enhanced understanding of basic immunobiology of gut-associated lymphoid tissues (GALT) will facilitate the development of alternate control strategy against these parasites. In chickens as in the mammalian system, the GALT contain both B and T lymphocytes which interact closely to protect the host against intestinal pathogens including parasites. For avian coccidiosis, local intraepithelial and lamina propria lymphocytes represent the main component of protective immunity to Eimeria. Because of the importance of cell-mediated immunity, coccidiosis vaccines must be capable of stimulating intestinal T cells. Although live and attenuated coccidia parasites have been applied to control coccidiosis, this disease continues to contribute to substantial morbidity and mortality in the poultry industry. Future successful development of an effective vaccine against coccidiosis will depend on further investigation of protective immunity to Eimeria infection and identification of important immunogenic parasite molecules. This review will highlight recent progress in avian intestinal immune system and vaccine development against major avian enteric parasites, Eimeria and Cryptosporidium.