Mechanisms for Congenital Transmission of Avian Leukosis Virus2

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Abstract
Chick embryos free from resistance-inducing factor (RIF) were given intravenous injections of avian leukosis virus (ALV) and allowed to hatch. Virologic and morphologic examination of older embryos and chicks established that all embryos given injections were infected with ALV and all hatched chicks were viremic at hatching. With the same procedures, uninfected RIF-free control embryos proved free of infectious virus, and no virus particles were found when sections of pancreases were examined with the electron microscope. In the infected birds, persistence of viremia was confirmed at various intervals after hatching (from 24 hours to 68 weeks). Samples of reproductive organs from hens of various ages and physiological states were examined with the electron microscope, and virus multiplication (budding particles) was evident in all. The largest concentrations of free virus particles and budding forms were in the albumen-secreting glands of the magnum during the ovulatory phase. These observations were confirmed in a second generation of hens derived from those initially infected with ALV, in which the congenital infection took place under natural conditions. Mechanisms for congenital transmission of ALV, based on infection of eggs in the reproductive systems of shedding hens, are discussed.