Abstract:
The problem. Concurrent infections with Marek's
disease (MD) and coccidiosis in chicken flocks have perplexed investigators for years. Infection with MD herpesvirus has been shown to inhibit immunity of chicks to three
species of Eimeria. Herpesvirus from turkeys (HVT) is used commercially as a vaccine against MD. This investigation studied the response to primary and secondary exposures to
E. acervulina oocysts in young chicks infected with either MDHV or HVT.
Procedure. Groups of chickens were inoculated with either MDHV or HVT. These chicks received a primary immunizing series of inoculations with E. acervulina oocysts. Individual chick weights were recorded during this period.
The chicks were subsequently challenged with a massive dose of E. acervulina oocysts. Following challenge chicks were monitored for weight gain or loss and for the number of
oocysts passed in the feces. Five to seven days following challenge all chicks were killed and autopsied to evaluate for E. acervulina and MD lesions. Data from these chicks were compared to data from control chicks which received oocysts but no virus.
Findings. Weight gains, oocyst recovery data, and autopsy observations for experimental and control chicks are equivalent.
Conclusions. Neither MDHV nor HVT had any effect upon the immune response of young chicks to E. acervulina. Vaccination of chicks with HVT did not jeopardize development
of resistance to E. acervulina.
Recommendations. Further studies with other strains of MDHV or with other species of Eimeria would be helpful in better understanding the relationship of MD and coccidiosis.
