Feline Immunodeficiency Virus and Feline Leukemia Virus

Feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) are two viruses that infect cats and cause significant, long-term health issues.

Feline immunodeficiency virus (FIV) is most commonly transmitted through bite wounds that cats get from fighting with other cats. Any cat can become infected with FIV. FIV is seen more commonly in outdoor only or indoor/outdoor, unneutered male cats because they are more likely to get into fights with other cats. When cats initially become infected with FIV, they may not show signs of illness or may have very mild illness for a short period of time. The virus can then be inactive for a prolonged period of time (months to years), during which cats are clinically normal. When active, the virus weakens the immune system. When it becomes active, cats may develop frequent infections including skin and upper respiratory infections or certain types of cancer.

Feline leukemia virus (FeLV) is typically transmitted from mother to kitten or between cats of the same household that groom one another, have prolonged close contact, or share water and food bowls. A cat that becomes infected with FeLV may clear the infection or may develop more significant illness from the virus (termed progressive infection). A small percentage of cats neither clear the virus nor have a progressive clinical course. Instead, the virus is dormant in the bone marrow for some period of time. These carriers do not show clinical signs until the virus is reactivated. Cats that are clinically affected by FeLV can develop anemia (low red blood cell count), certain types of cancer, significant inflammation of the mouth/gums, persistent fever, and are prone to secondary infections of the skin, urinary tract, and respiratory tract. Some of these cats may lose weight and have poor haircoats.

Most cats are tested for FIV and FeLV when they’re young or when they’re newly adopted. Because these infections are prevalent, if your cat goes outside often, gets in fights with other cats, or becomes sick with something else (for example, frequent infections or unexplained anemia), your vet may advise re-testing. If you have any concerns about FeLV or FIV, please discuss these with your primary care veterinarian.