medical Definition of avian leukosis
: any of a group of diseases (as lymphoid leukosis) of poultry that are caused by strains of a retrovirus (species Avian leukosis virus of the genus Alpharetrovirus), that involve disturbed blood formation, and that are distinguished individually by special manifestations (as paralysis, tumor formation, leukemia, and eye damage) — called also
avian leukosis complex
