Strategies for anti-coccidial prophylaxis

Abstract

SUMMARYCoccidiosis, a serious disease resulting from infection with parasitic protozoa of the genusEimeria, causes significant economic losses to the poultry industry, where intensive rearing facilitates transmission of infectious oocysts via the fecal/oral route. Current control relies primarily on prophylactic drugs in feed but, whilst cost effective, the rise of drug resistance and public demands for residue-free meat has encouraged development of alternative control strategies. Chickens that recover from infection withEimeriadevelop solid immunity that is directed against the early asexual stages of the parasite life cycle. This has allowed development of a number of vaccines that utilize deliberate infection with controlled doses of virulent oocysts or reproductively attenuated lines ofEimeria.The latter are immunogenic but non-pathogenic. The realization that both prophylactic drugs and attenuated vaccines control but do not eradicate infection withEimeriaencouraged development of a vaccine based upon maternal immunity. Laying hens exposed toEimeriaare able to transfer protective antibodies to hatchlings via egg yolks and these antibodies have been used to identify parasite proteins that are conserved across the genus. When delivered maternally, these provide an economical means of preventing coccidiosis, offering immediate protection to newly hatched chicks.