Epidemiology of reticuloendotheliosis virus in broiler breeder flocks

Six broiler breeder flocks from two companies in Mississippi were tested at intervals for reticuloendotheliosis (RE) virus infection. Virus was isolated and antibody demonstrated in all six flocks. Infection was first detected at ages ranging from 13 to 47 weeks. Studies showed that neither congenital transmission from grandparent flocks nor treatment with contaminated vaccines was a likely source of infection; thus, exposure to RE virus was assumed to come from the environment. Virus was isolated from litter samples from two of the flocks, but no specific environmental infection source was identified. Infection rates of flocks differed between the two companies. Although adequate controls were lacking, no performance problems due to RE virus infection were apparent in breeder or broiler progeny flocks. However, the RE viruses isolated from these flocks were immunosuppressive and oncogenic when inoculated into day-old chicks. A moderate (3-16%) incidence of neoplasms was induced by contact exposure to these field isolates in the laboratory.