Detection of avian leukosis virus with the ELISA system: evaluation of conjugation methodology and comparison of sensitivity with the phenotypic mixing test in commercial layer flocks.

Conjugates of horseradish peroxidase with rabbit IgG antibody against gs antigen (p27) of avian myeloblastosis virus were prepared using glutaraldehyde and periodate methods of coupling. Conjugates were evaluated for the detection of gs antigen of avian leukosis and sarcoma viruses in the ELISA system and the periodate conjugate was found to be superior. With an ELISA based on a periodate conjugate it was possible to detect 5 x 10(3) IU of leukosis virus propagated in cell culture. Comparisons between the PM test and ELISA on biological samples showed the PM test to be 2 to 2,000 times more sensitive than ELISA for vaginal swabs and embryo extracts. ELISA was 16 to 64 times more sensitive than the CF test when comparisons were made on albumens and embryo extracts. When the ELISA was used for testing vaginal swabs for the prevalence of LLV infection in commercial laying flocks, it appeared that the reliability of ELISA varied. In all five flocks studied, ELISA detected a higher percentage of gs+ [virus+] hens than did the PM test, the proportion of ELISA(+) PM(-) samples ranging from 3 to 53%. In some flocks ELISA failed to detect a low proportion [ 1 to 5%] of infected hens when vaginal swabs were used for screening. The suitability of ELISA for use in screening of commercial flocks for LLV infection is discussed.