Reduction of Reticuloendotheliosis in Foundation Breeding Flocks of Chickens: A Combined Immunological and Molecular Biological Approach

Abstract

Reticuloendotheliosis virus (REV) is an avian retrovirus that can cause immunosuppression, growth retardation and tumors. An attempt to define the extent of the economic damage to the poultry industry that it causes is discussed in this report. In addition to losses experienced by commercial laying flocks, reduced rates of hatchability and embryo developmental disorders were demonstrable due to vertical transmission of the virus. I. Eradication of REV In this project a comprehensive national program was applied for the eradication of REV from Israeli breeding stocks by the elimination of antibody-positive birds from the breeding program. The prevention of REV-infected breeders entering Israel was also implemented by serological examination of imported day-old chickens and turkeys for maternal antibody. At the same time commercial breeding flocks in Israel were surveyed routinely to measure the extent of environmental exposure to REV throughout Israel. II. Economic factors associated with vertical transmission on breeders and progeny It was observed that on some poultry farms exposure of breeding flocks to viral infection, if it occurs when the birds are immunocompetent, leads only to a seroconvertion event. In these flocks no differences were demonstrated between the performances of seronegative and seropositive birds. When the F1 generation was selected according to seronegativity of the parents, all the progeny were seronegative, indicating that tolerantly infected birds did not form a significant proportion of the parent flock. In sharp contrast, breeding flocks that became exposed to the virus about the point of lay or during the laying period, shed virus vertically for a brief period of time through the egg. Our epizootiological observations lead us to conclude that the progeny (laying pullets) becomes tolerantly infected and are immunosuppressed as they increase in age. Increased mortality and susceptibility to intercurrent diseases were recorded.