Isolation and some characteristics of a subgroup J-like avian leukosis virus associated with myeloid leukosis in meat-type chickens in the United States

Several subgroup J-like avian leukosis viruses (ALV-Js) were isolated from broiler breeder (BB) and commercial broiler flocks experiencing myeloid leu kosis (ML) at 4 wk of age or older. In all cases, diagnosis of ML was based on the presence of typical gross and microscopic lesions in affected tissu es. The isolates were classified as ALV-J by 1) their ability to propagate in chicken embryo fibroblasts (CEF) that are resistant to avian leukosis vi rus (ALV) subgroups A and E (C/AE) and 2) positive reaction in a polymerase chain reaction with primers specific for ALV-J. The prototype strain of th ese isolates, an isolate termed ADOL-Hcl, was obtained from an adult BE flo ck that had a history of ML. The ADOL-Hcl was isolated and propagated on C/ AE CEF and was distinct antigenically from ALV of subgroups A, B, C, D, and E, as determined by virus neutralization tests. Antibody to ADOL-Hcl neutr alized strain HPRS-103, the prototype of ALV-J isolated from meat-type chic kens in the United Kingdom, bur antibody to HPRS-103 did not neutralize str ain ADOL-Hcl. On the basis of both viremia and antibody, prevalence of ALV- J infection in affected flocks was as high as 87%. Viremia in day-old chick s of three different hatches from a BE flock naturally infected with ALV-J varied from 4% to 25%; in two of the three hatches, 100% of chicks that tes ted negative for virus at hatch had evidence of viremia by 8 wk of age. The data document the isolation of ALV-J from meat-type chickens experiencing ML as young as 4 wk of age. The data also suggest that strain ADOL-Hcl is a ntigenically related, but: not identical, to strain HPRS-103 and that conta ct transmission of ALV-J is efficient and can lead to tolerant infection.