06/10/2026
Feline leukemia virus (FeLV) is a virus that infects cats. It was first identified in cats that had a form of leukemia (cancer of the white blood cells), but it is now known to cause a range of serious health problems.
FeLV depresses the immune system, making infected cats more prone to infections, anemia, and certain cancers. Like all viruses, FeLV can only reproduce inside living cells. FeLV only infects members of the cat family and is not a risk to other animal species or humans.
FeLV invades various cells of the cat's immune system and blood-forming tissues. This invasion causes the cell to die or creates a mutation (change) in the cell’s genetic code, which can make the cell potentially cancerous, although it may not happen for months to years after the infection. FeLV infection can lead to cancers in a variety of tissues, organs, and body sites. When it affects cells in the bone marrow, it can cause blood cancer like leukemia (elevated circulating white blood cells).