Cause
The most common way that cats become infected with the feline leukemia virus is through direct contact with the saliva or nasal secretions of an infected feline -- which often occurs during a fight when a cat with the virus bites an unvaccinated animal. The virus cannot survive in the environment, so urine and feces are not significant sources of infection to other cats. In addition, routine disinfectants will eliminate the virus from cages and other surfaces. However, cats that groom each other and share food and water sources can transmit the virus because the saliva of an infected cat is contagious. Less commonly, the virus can be passed from a mother cat to unborn kittens in the uterus. Mother cats also can transmit the disease while grooming or nursing the kittens.