THE PATTERN OF CONGENITAL TRANSMISSION OF AN AVIAN LEUKOSIS VIRUS

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Abstract
Sera were collected by repeated bleeding over a period of 10 months from a flock of chickens which had been selectively bred for a high incidence of lymphomatosis. The sera were assayed for the presence of RIF, a virus indistinguishable from lymphomatosis virus. The sera were also tested for antibodies to RIF and to RSV which is immunologically related to RIF. Seven of the 26 birds had high concentrations of RIF and these showed no appreciable change in virus titer throughout the period of study. None of the viremic birds had antibody to RIF and only one had antibody to RSV. The remaining 19 birds were nonviremic but had antibody of RIF, and 15 had antibody to RSV. The antibody titer remained relatively constant during the period of investigation. Three of the 4 viremic hens were fertile and most of their embryos proved to be infected. There was no indication that the 3 viremic roosters in the study transmitted virus to their progeny despite the fact that a high proportion of cells in the testes were actively producing virus. Only one of the 12 fertile nonviremic hens regularly infected her progeny. This single case, however, demonstrated that RIF could continue to multiply in the ova despite the presence of high concentrations of antibody. High proportions of cells in most congenitally infected embryos were found to be actively producing virus. It was held likely that the persistent high viremia in adults was the result of the early exposure of birds to high concentrations of virus leading to an immunological tolerance to the virus.