Comparison of complement fixation and phenotypic mixing tests for the detection of lymphoid leukosis virus in egg albumen and embryos of individual eggs

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Abstract
Individual eggs, collected from 14 hens over a period of 10 weeks, were tested for lymphoid leukosis (LL) virus by four methods. The chickens were selected from a conventional flock on the basis of virus recovery from embryos 3 months earlier. Albumen samples and extracts of embryos were examined by complement fixation (CFT) and phenotypic mixing tests (PMT). Most eggs positive for LL virus (LLV) and/or group specific (gs)‐antigen were detected by testing of embryo extracts by PMT and CFT. Examination of albumens yielded less LLV and gs‐antigen positive eggs. However, because a few birds produced eggs with predominantly gs‐antigen in the albumen and less frequently with virus in the embryos from the same eggs, the combination of CFT on both albumen and embryo extract proved to be the most sensitive detection system. CFT on both albumen and embryo are easier to perform than PM tests and therefore may be useful in LL eradication programmes. The majority of the hens intermittently transmitted virus and/or gs‐antigen to embryos. The results of this study indicate that congenital transmission patterns of LLV infections may be different in individual birds.