Submitted to: Veterinary Parasitology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/17/2009
Publication Date: 5/18/2009
Citation: Jenkins, M.C., Fetterer, R.H., Miska, K.B. 2009. Co-infection of chickens with Eimeria praecox and Eimeria maxima does not prevent development of immunity to Eimeria praecox or Eimeria maxima. Veterinary Parasitology 161:320-323. Interpretive Summary: Avian coccidiosis is an intestinal disease primarily of poultry that causes U.S. broiler producers an annual loss of over $ 350 million, with losses worldwide exceeding $ 1 billion. The disease has been controlled for decades by medication of feed with anti-coccidial drugs, but the appearance of drug-resistant strains of Eimeria and increased consumer pressure to reduce use of medicated feeds has prompted alternative control measures. One approach that has met with success is vaccination of day-old chicks with a mixture of low doses of virulent or attenuated Eimeria oocysts. Our studies have shown that one species, namely E. praecox, is prevalent in poultry farms. A previous report showed that infecting chickens with a mixture of non-pathogenic E. praecox and pathogenic E. maxima could prevent overt clinical symptoms associated with the latter species. The purpose of the present study was to determine if immunity to coccidiosis was affected by coinfection of chickens with E. praecox and E. maxima. This was done for two reasons- (1) to determine if including E. praecox in a vaccine formulation would prevent immunity to E. maxima, and (2) to gain an understanding of the non-specific immunity that develops in a primary Eimeria infection. Our studies revealed that complete immunity is elicited against both E. maxima and E. praecox in chickens co-infected with both species. These findings indicate that incorporating E. praecox in a commercial live oocyst vaccine should not hamper the development of immunity to other Eimeria, namely E. maxima.
Technical Abstract: Previous studies revealed an ameliorating effect of Eimeria praecox on concurrent E. maxima infection, such that weight gain, feed conversion efficiency, and intestinal lesions were nearly identical to uninfected or E. praecox-infected controls. The purpose of the present study was to determine if protective immunity against E. maxima challenge infection developed in chickens infected with both E. praecox and E. maxima. Day-old chickens were infected with 103 E. praecox, 103 E. maxima, or a mixture of 103 E. praecox and 103 E. maxima oocysts. Chickens were then challenged at 4 weeks of age with 5 x 104 E. praecox or 5 x 103 E. maxima oocysts and clinical signs of coccidiosis were assessed 7 days post-challenge. Relative to non-challenged controls, naïve chickens or chickens immunized with E. praecox displayed a 32-34 % weight gain depression after challenge with 5 x 103 E. maxima oocysts. In contrast, chickens immunized with either E. maxima oocysts alone or a combination of E. praecox and E. maxima oocysts displayed complete protection against lower weight gain associated with E. maxima challenge. Also, protection against decreased feed efficiency and intestinal lesions was observed in single E. maxima- or dual E. maxima+E. praecox-immunized chickens. These findings indicate that co-infection of chickens with E. maxima and E. praecox does not prevent development of immunity against E. maxima or E. praecox infection.