The use of Elisa for detection of exogenous and endogenous avian leukosis viral antigens in basic breeding flocks

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Abstract
An enzyme‐linked immunosorbent assay (ELISA) for avian leukosis/ sarcoma virus (ALV) group‐specific (gs) antigens was used to study the identification of hens which congenitally excrete exogenous ALV. The sensitivity of this assay was compared with that of the pheno‐typic mixing test (PMT) and the direct complement fixation test (CFT) by testing limiting dilutions of purified avian myeloblastosis virus (AMV), embryo homogenates and albumens. About 0.4 ng/ml of purified AMV protein could be detected by ELISA and 23.8 ng/ml of AMV protein was demonstrable by the CFT. The lowest levels of gs‐antigen detection corresponded with about 100 median tissue culture infectious doses (TCID50 ) of infectious ALV. Albumens and embryos of three White Leghorn flocks and one White Plymouth Rock flock were tested for the presence of avian leukosis virus (ALV) gs‐antigens by the complement fixation test (CFT) and the enzyme‐linked immunosorbent assay (ELISA) and exogenous ALV employing the phenotypic mixing test (PMT). The highest number of ALV‐gs antigen positive samples of egg albumens was obtained by the ELISA. In embryo homogenates prepared from eggs of the four flocks under study 100% scores for gs‐antigens were obtained by ELISA. A differentiation between gs‐antigens of endogenous and exogenous ALV was made by testing of supernatant fluids after one chick embryo fibroblast passage of the C/E phenotype. Endogenous viral (ev) genes leading to the expression of endogenous ALV gs‐antigens were apparently present in practically all chickens of the four flocks under study. Complete endogenous ALV (subgroup E) was detected in embryos (41%) from the White Plymouth Rock grandparent flock, but was not found in embryos of two White Leghorn basic breeder flocks. The results indicate that both flocks of White Leghorn chickens are endowed with ev 3 genes. Circumstantial evidence was obtained for the prevalence of endogenous ALV gs‐antigens in albumen samples of eggs from flocks with gs+chf+ and V‐E+ phenotype respectively.