Lymphoid leukosis: interrelations among virus infections in hens, eggs, embryos, and chicks.

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 one or more eggs with virus in albumen 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 albumen prior to incubating eggs identified all hens that transmitted infection. For example, 14 hens negative on VST produced 50 eggs negative for virus in albumen and yet one of the embryos from these eggs was infected. Eggs from other hens had infectious virus in albumen and about half of the embryos from these were infected. Tests for virus in cloacal swabs from one-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 10(7) infectious units per ml. The cloacal swab test should be a valuable adjunct to the VST and tests on egg albumen in programs designed to eradicate lymphoid leukosis from chickens.