Field Application of a Subunit Vaccine against an Enteric Protozoan Disease

Abstract

BackgroundCoccidiosis is a major global veterinary health problem in intensively reared chickens. It is caused by apicomplexan parasites of the genus Eimeria.Principal FindingsA subunit vaccine composed of purified antigens from the gametocytes of Eimeria maxima was used to stimulate the production and transfer of maternal antibodies between breeding hens and their hatchlings. The vaccine was injected into hens twice before they began laying eggs. Immunization had no adverse affects on egg laying or health of the hens and resulted in high antibody levels throughout the life of the hens. Progeny of immunized hens excreted significantly less oocysts of various species of Eimeria in their faeces than chicks from unvaccinated hens. Furthermore, the offspring of vaccinated hens developed stronger natural immunity to Eimeria, so that they were resistant to challenge infection even at 8 weeks of age, well after all maternal antibodies had left their circulation. Field trials were conducted in South Africa, Brazil and Thailand, involving at least 1 million progeny of vaccinated hens and at least 1 million positive control birds (raised on feed containing anticoccidial drugs or immunized with a live vaccine) in each country. Additionally, trials were carried out in Israel involving 60 million progeny of vaccinated hens and 112 million positive control birds. There were no significant differences in growth rate, feed conversion ratios or mortality in the offspring of vaccinated hens compared with the positive control chickens in any of these countries regardless of different management practices, different breeds of chickens or climate.ConclusionsThese results demonstrate that a vaccine composed of antigens purified from the gametocytes of Eimeria can be used safely and effectively to prevent the deleterious effects of coccidiosis. It is the first subunit vaccine against any protozoan parasite to be successfully applied on a commercial scale.

Vaccination against parasites – status quo and the way forward

“…This technology requires the use of animals for production of vaccines with all its disadvantages (biosafety, ethical concerns etc.). Lately, a subunit vaccine against Eimeria maxima of chicken was developed and marketed for use in maternal immunization [36, 42]. Although it is also produced in animals and its lasting success in the field still remains to be evaluated, the concept of inactivated vaccines against parasites has received a significant incentive with this development.…”

Designing strategies for the control of coccidiosis in chickens on poultry farms using modern diagnostic tools

“…This picture is seen whether the farm management system is based on the use of new or recycled litter. 11,12 In addition, farmers will provide a 3-to 4-week break period prior to bringing in the next flock of chickens. This allows the number of oocysts to reduce to very low numbers at the start of each grow-out period.…”

“…10 However, in commercial poultry houses under cramped and stressful conditions, the highly resilient oocysts build up in the feces to very large numbers (100-300,000 oocysts per gram of litter). 11,12 Young broiler (meat-producing) chickens are not homogeneously exposed to the parasite for the first 1-2 weeks of growth, and as a result many of them are highly susceptible to infection at 3-5 weeks of age when there is a large number of oocysts in the litter. This results in severe clinical disease and sometimes even fatal consequences.…”

“…11,[18][19][20][21] The research and development of these vaccines also relies on an accurate and sensitive way of determining the identity and purity of Eimeria strains used. For basic research, the incursion of contaminating Eimeria parasites in presumably purified strains can lead to invalid interpretation of data.…”

Prokaryotic expression and identification of 3-1E gene of merozoite surface antigen of Eimeria acervulina

“…However, conventional vaccines including live or attenuated vaccines could cause severe adverse reactions (Vermeulen et al 2001). Subunit vaccines of Eimeria carrying encoding antigen gene fragments induce protective immunity against challenge infection (Garcia et al 2008;Song et al 2010) and are proven to be safe and effective means to prevent the deleterious effects of coccidiosis (Wallach et al 2008). …”