Feline leukemia virus (FeLV) is one of the major causes of illness and death in domestic cats. The virus is contagious and spreads primarily through intimate nose-to-nose contact with infected saliva. This very often occurs during cat fights, grooming, and mating. Contaminated urine, blood, and feces are also sources of infection. The virus can cross the placenta, infecting kittens while still in the mother's uterus. Nursing kittens can become infected from contaminated milk if the queen is infected with the virus.