Lymphoid Leukosis Virus: A Survey of Commercial Breeding Flocks for Genetic Resistance and Incidence of Embryo Infection

Viruses in the avian leukosis-sarcoma group are known to cause a number of neoplasms, including visceral lymphomatosis (lymphoid leukosis), erythroblastosis, myeloblastosis, myelocytomatosis, nephroblastomas, endotheliomas, sarcomas, and possibly osteopetrosis. Infection by any one of the viruses in this group causes the formation of a group-specific antigen detectable by the COFAL test, a complement-fixation procedure (17). Properties reliant upon the viral coat antigens, however, have permitted the identification of at least 3 distinct subgroups (A, B, and C), two of which (A and B) are known to exist in commercial chicken populations (4,14,15). These properties are: 1) antigenicity, as measured by neutralization or fluorescent antibody procedures; 2) ability to induce resistance to a given strain of Rous sarcoma (RSV) in chick embryo fibroblasts; and 3) infectivity for various genetically defined cell populations. Several of the types, e.g. lymphoid leukosis (LLV), avian myeloblastosis (AMV), and RSV, have strains representing more than one subgroup (14,15). Rubin, who first noted the resistance phenomenon in 2 above, introduced the acronym RIF, for resistance-inducing factor, for an isolate of LLV (12). The term virus has since been loosely applied to other similar isolates, and RIF activity has referred to the resistance phenomenon regardless of the type.