Lymphoid Leukosis: Interrelations among Virus Infections in Hens, Eggs, Embryos, and Chicks

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Abstract
Hens from a commercial source were selected because they were infected with lymphoid leukosis virus (LLV). LLV was detected in vaginal swabs from 17 viremic hens and from 27 of 44 hens that were not viremic. All hens that were positive on the vaginal swab test (VST) produced 1 or more eggs with virus in albumin or in embryos, whereas in comparable tests, virus was detected only in eggs from 5 of 17 hens that were negative on VST. Congenital transmission of LLV was erratic and neither the VST nor tests for virus in egg albumin prior to incubating eggs identified all hens that transmitted infection. For example, 14 hens negative on VST produced 50 eggs negative for virus in albumin and yet one of the embryos from these eggs was infected. Eggs from other hens had infectious virus in albumin and about half of the embryos from these were infected. Tests for virus in cloacal swabs from 1 day old chicks were as sensitive as tests on embryos for detecting congenital transmission. Titers of LLV in the meconium of congenitally infected chicks were as high as 107 infectious units/ml. The cloacal swab test should be a valuable adjunct to the VST and tests on egg albumin in programs designed to eradicate lymphoid leukosis from chickens.