Feline leukemia virus (FeLV) is a retrovirus that infects cats. As a retrovirus, the genetic information of FeLV is carried by RNA instead of DNA. FeLV is usually transmitted between infected cats when the transfer of saliva or nasal secretions is involved. If not defeated by the animal’s immune system, the virus can be lethal.

FeLV causes immunosuppression in pet cats, and there is also evidence for existence of the virus in larger wild cat populations also (e.g. Lynx, Cheetah, and Lion). Overwhelming epidemiologic evidence suggests FeLV is not transmissible to either humans or dogs.

Note: Despite the its name, the disease is not a form of cancer. The name stems from the fact that the first disease associated with the virus was a form of leukemia, and by the time it was discovered that the virus was the causal agent, the misleading name was already being used by pet owners.