Feline leukemia virus (FeLV) can cause many different diseases in domestic cats - from an immuno-suppressive syndrome to cancer. While many cats are able to resist the infection or show minimal side effects, about one-third of infected cats become sick and die.
About 1% to 5% of the cats that are allowed to roam free will be lifetime carriers of the virus. Carrier cats shed the virus in their saliva, urine, and feces. Also, cats can transmit the disease when they fight, bite and groom each other. The virus is usually introduced to indoor populations through the inadvertent introduction of a healthy appearing FeLV carrier cat.
Diseases like chronic mouth and gum infections, skin and ear infections, and chronic respiratory disease can indirectly be a result of FeLV. Tumors, anemia, feline distemper and reproductive disorders are directly caused by feline leukemia virus.