Avian leukosis virus subgroup J infection profiles in broiler breeder chickens: Association with virus transmission to progeny

Profiles of infection with avian leukosis virus subgroup J (ALV-J) and fact ors that predict virus transmission to progeny were studied. Eggs from an i nfected broiler breeder flock were hatched at the laboratory. The flock was reared in a floor pen, transferred to laying cages at 22 wk, and inseminat ed to produce fertile eggs. A cohort of 133 chickens was tested at frequent intervals over a 62-wk period for virus, viral antigens, or antibodies in plasma, cloacal swabs, egg albumen, and embryos. Virus was detected in 7% o f chicks at hatch but spread rapidly so that virtually all chicks became in fected between 2 and 8 wk of age. Mortality due to myeloid leukosis and rel ated tumors was 22%. Over 40% of the chicks developed persistent infections , whereas the remainder experienced transient infections. Five types of inf ection profiles were recognized. Novel responses included hens that were po sitive for virus intermittently or started late in life to shed viral antig ens into the cloaca. ALV-J was isolated from 6% of 1036 embryos evaluated b etween 26 and 62 wk. However, over 90% of the virus-positive embryos were p roduced between 29 and 34 wk of age. Of 80 hens that produced embryos, 21 p roduced at least one infected embryo and were identified as transmitters. A ll but one transmitter hen would have been detected by a combination of vir emia, cloacal swab, and albumen tests conducted between 18 and 26 wk Howeve r, virus was transmitted to embryos from hens that were not persistently vi remic or that rarely shed viral group-specific antigen into the albumen of their eggs, intermittent patterns of both antigen shedding and virus transm ission to embryos were observed in some hens. These results validate curren t screening procedures to identify potential transmitter hens and provide s ome suggestions for improvement bur also show chat identification of all tr ansmitter hens by such procedures is unlikely. Thus, eradication programs b ased solely on dam testing may be less effective than those where dam testi ng is combined with procedures to mitigate early horizontal transmission in progeny chicks.