Associations have been studied between natural infection of hens and cocks in a commercial flock with subgroup A lymphoid leukosis virus (LLV) and the presence of LLV in their eggs and progeny. Whole blood and sera were examined for LLV and virus-neutralising antibody, and vaginal swabs and semen samples were examined for LLV. Egg albumen samples were tested for LLV and group-specific (gs) antigen and embryos for LLV. Of 198 hens, 63.6% were immune, non-viraemic, 7.1% tolerant viraemic, 2.5% immune, viraemic and 26.8% non-immune, non-viraemic. Genetic resistance may have accounted for the last of these classes. A low rate of infection was found in the 40 cocks studied and the possible reason for this is discussed. There was no evidence that they were responsible for congenital transmission of LLV. Strong associations were observed between LLV in vaginal swabs or serum of hens and LLV or gs-antigen in albumen in their eggs. Significant but weaker associations were observed between these traits in the hens and LLV in their embryos, and between LLV and gs-antigen in egg albumen and LLV in embryos. Testing of whole blood for LLV showed little advantage over testing of serum. The efficiency of various tests for detecting hens least likely to transmit LLV to their progeny was examined. The lowest rates of embryonic transmission, which were 7-fold lower than the overall transmission rate, occurred in hens of two classes: those negative for viraemia, LLV in vaginal swabs, and antibodies, and those negative for LLV in vaginal swabs, antibodies and LLV or group-specific antigen in their egg albumen. The implications of these findings are discussed.

(1982) Further studies on the eradication and Epizootiology of lymphoid leukosis virus infection in a commercial strain of chickens, Avian Pathology, 11:1,[145][146][147][148][149][150][151][152][153][154][155][156][157][158][159][160][161][162] Agricultural Research Council Statistics Group Department of Applied Biology, Pembroke StreetCambridge, England SUMMARY The feasibility of eradicating exogenous lymphoid leukosis virus (LLV) from a commercial egg-layer grandparent strain of chickens was examined by selecting replacement chicks from hens expected to have a reduced likelihood of transmitting LLV, followed by testing of progeny chicks and removal of those showing evidence of infection, together with their early contacts. Chicks from unselected hens were hatched and reared separately for comparison.The selected chicks came from hens negative for LLV in vaginal swabs and for LLV and/or group-specific antigen (gsa) in egg albumen, but at hatching 2.5% were infected by LLV in cloacal swab tests compared with 4.1% of unselected chicks, an insignificant difference. The infected chicks from the selected group, and their cage mates, were culled, leaving 85 hens of which seven were identified at different times as being infected and were removed. At 70 weeks 75 hens remained free of LLV infection. Of 369 eggs laid by the selected hens, 0.3% contained LLV in the albumen, and none contained gsa in albumen or LLV in corresponding embryos. Chicks hatched from the selected group were free of LLV infection.LLV infection was allowed to spread naturally in the unselected hens and 85.4% were infected at 70 weeks. Of these hens, 60.0% produced eggs with LLV in albumen, 41.2% with gsa in albumen, and 32.9% with LLVinfected embryos. Of 509 eggs from these hens, 25.1% had LLV in albumen, 30.5% had gsa in albumen, and 10.4% had LLV-infected mebryos.In confirmation of other studies, shedding of LLV to egg albumen and to

Encapsulated and non-encapsulated variants of one strain of gonococcus were compared for their capacity to produce infection in chambers implanted subcutaneously in mice, for their reactions with specific antibody and for their precipitation with wheat germ agglutinin. Only the encapsulated variant could infect implanted chambers. Specific rabbit antiserum raised against the non-encapsulated variant killed both variants. Saline extracts and lipopolysaccharide preparations of the encapsulated variant differed from those of the non-encapsulated one in their reactions with wheat germ agglutinin and antibody in diffusion and electrophoresis tests. Preparations from infective encapsulated gonococci reacted with wheat germ agglutinin while those from the non-encapsulated variant did not. Immunodiffusion tests showed that lipopolysaccharides from both variants share a common antigenic determinant, but saline extracts and lipopolysaccharides from encapsulated gonococci possess an additional determinant. The significance of these findings is discussed.