Sustainable coccidiosis control in poultry production: the role of live vaccines.

The development of new methods of administering coccidiosis vaccines has facilitated their use in the hatchery and thereby improved prospects for the economic vaccination of broilers. The acquisition of protective immunity to Eimeria species is boosted by further exposure to infection after vaccination. Factors that affect the reproductive efficiency of non-attenuated and attenuated vaccines are considered and the key role that oocyst production plays in establishing and maintaining uniform immunity in a flock of chickens is discussed. In addition to immunisation, a possible advantage to the application of certain vaccines is that their use could repopulate poultry houses with drug-sensitive organisms. Theoretical rotation programmes in which the use of drugs is alternated with that of vaccines are described. Variability of the cross-protective immune response between strains of the same species should be considered during vaccine development and subsequent use. The significance of less common species of Eimeria, not included in all vaccines, also needs to be assessed. An important consideration is the occurrence of pathogens other than Eimeria (such as the bacterium Clostridium) in flocks given coccidiosis vaccines and the methods by which they might be controlled. More research is required into the relationship between bacterial and viral infections of poultry and coccidiosis vaccination. Vaccines need to be developed that are simple to apply and cost effective for use in areas of the world where small-scale poultry production is commonplace. In the near future it is likely that more live vaccines based upon oocysts derived from attenuated strains of Eimeria will be developed but in the longer term vaccines will be based on the selective presentation to the host of specific molecules that can induce protective immunity. This achievement will require significant investment from the private and public sectors, and, if successful, will facilitate the sustainable control of coccidiosis in poultry production.