Analysis of avian leukosis virus infections with an enzyme immunoassay

An enzyme-linked immunosorbent assay (ELISA) for avian leukosis virus group-specific antigen was used to study infections with and shedding of avian leukosis virus in a commercial flock of chickens with a known high incidence of infection. Avian leukosis virus group-specific antigen was detected in serum or cloacal washings from 76% of a group of 100 61-week-old hens. With eggs collected during the next 3 weeks, antigen was detected in the albumen of 88% of the eggs from ELISA-positive hens and 2% of the eggs from ELISA-negative hens. Results of assays for infectivity correlated closely with the ELISA results. Serum and cloacal specimens were almost equally sensitive in detecting infection; however, a higher proportion of cloaca-positive hens (97%) than serum-positive hens (91%) shed virus in their eggs. Similar results were obtained from a second sampling of eggs taken when the hens were 84 weeks old, after an intervening molt. Avian leukosis virus infection was correlated with reduced egg production and increased mortality. Eggs were produced by 100% of the ELISA-negative birds during both sampling periods, whereas only 69% of the ELISA-positive birds produced eggs at 61 weeks and 76% produced eggs at 84 weeks. All birds that were ELISA negative at 61 weeks survived the experiment. Of 14 ELISA-positive birds that died and were examined postmortem between 61 and 84 weeks, 8 had malignancies, and the remainder died of a variety of nonmalignant diseases.