ALV-J is an avian retrovirus first isolated in meat-type chickens in the late 1980s, and is designated as a unique subgroup partly based on the envelope glycoprotein (gp85).
Clinically, ALV-J causes predominantly myeloid leukosis, with variable tumor frequency across chicken lines. As with other avian leukosis viruses, ALV-J is transmitted both vertically (congenital infection of the egg albumin and the chick embryo) and horizontally (through close contact with infected chicks). This test was designed as a screening tool using serum samples from flocks 10 weeks of age or older.