Influence of Endogenous Viral (ev) Gene Expression and Strain of Exogenous Avian Leukosis Virus (ALV) on Mortality and ALV Infection and Shedding in Chickens

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Abstract
Two experiments were conducted to determine the influence of ev gene expression on the response of chickens to day-old inoculation with 2 laboratory and 2 field strains of avian leukosis virus (ALV). The ev2- and ev3-negative semi-congenic chickens had much higher mortality from a unique nonneopalstic syndrome (NNS) than ev2- and ev3-positive semi-congenic chickens after inoculation with ALV strain Rous-associated virus-1 (RAV-1). The 3 other ALV strains induced little NNS. All 4 strains of ALV induced higher incidences of neutralizing antibody and lower incidences of viremia in ev2- and ev3-negative chickens than in ev2- and ev3-positive chickens. The semi-congenic ev2- and ev3-negative chickens were only slightly less likely to shed ALV in the cloaca. Chickens of line 0, an unrelated line lacking ev genes, had a much higher rate of antibody production and lower rate of viremia and shedding than the semi-congenic chickens. Line 0 failed to get NNS after RAV-1 inoculation. There were major differences among strains of ALV in induction of antibody response, viremia and shedding in the cloaca. The 2 field strains of ALV tended to be less immunogenic than the laboratory strains. Evidently, both the genetics of the host, including variation in ev gene expression, and the strain of ALV can influence the probability of ALV shedding and congenital transmission after horizontal infection.