General Information:

FeLV (Feline Leukemia Virus) and FIV (Feline Immunodeficiency Virus) are both similar viral infections of cats. Both viruses are classified as retroviruses — the same viral class as HIV in people. Infection is considered serious.

Both viruses result in suppression of the immune system. Initially, cats may not show any symptoms. Over time, however, affected cats are prone to opportunistic infections and chronic fever. Affected cats also tend to have a poor appetite, lose weight, and have chronic diarrhea.

Cats infected with FeLV are more likely to develop tumors and anemia than those cats infected with FIV. Cats infected with FIV are more likely to suffer from problems with the mouth and gums and to have eye disease than those cats infected with FeLV.
In our experience, cats infected with FIV tend to do better long-term than those cats infected with FeLV. FIV-positive cats may live well into adulthood. FeLV-positive cats, however, often die within 2-3 years of exposure. Cats infected with both viruses often do very poorly.

FIV is primarily spread via bite wounds in cats that roam outdoors; non-neutered male cats are often affected since they are more likely to fight. There is some evidence that cats older than 6 years are more susceptible to FIV infection than younger cats. This may at least partially explain why we often see older FIV-positive cats.

FeLV may also be spread via bite wounds, but is more commonly transmitted through mutual grooming and sharing of food bowls and water dishes. An FeLV-positive cat represents a real threat to the other cats in a multicat household and should be isolated from its housemates. Young cats appear to be at highest risk for FeLV infection


We recommend testing all new cats and kittens prior to introduction into the household. A simple blood test is available that is very accurate. On occasion, a cat/kitten who tests positive for infection may test negative a few months later. Apparently some cats are able to fight off an infection. More sophisticated tests are available that can help confirm or refute infection if a positive result is obtained on the initial test.


An effective vaccine is available for FeLV. The vaccine series should be started at 10-12 weeks of age with a booster 3-4 weeks later. Annual boosters are required. We only recommend vaccination for those cats at risk (e.g., cats who go outdoors, cats who live with another cat that goes outdoors, or cats who live with an FeLV-positive cat in the same household).
A vaccine has recently been approved for FIV. A few controversial issues still exist with this vaccine, however, so we are not recommending its use at this time.


There is no cure for these viruses. Treatment is largely symptomatic and supportive. Symptoms such as upper respiratory infections should be treated aggressively and early. Nutritional support may also be necessary to maintain a healthy body weight.

In general, affected cats should be examined by a veterinarian at least twice per year — even if not showing any symptoms. It is important to monitor affected cats carefully so that potential problems can be found early.

Antiviral and immunostimulant medications have been used experimentally, but remain unproven. The cost and side effects of these drugs often limits their practical use.