Pet Alliance of Greater Orlando veterinarian, Dr. Julie Andersen, explains feline leukemia virus (FeLV), an ailment that impacts millions of cats globally.

Feline leukemia virus (FeLV) infection affects cats in different ways. Some cats can be completely free of any clinical signs if their immune system is able to handle the virus well. Other cats can develop secondary infections with other viruses and bacteria due to immunosuppression. Some cats unfortunately develop cancers such as leukemia and lymphoma or profound anemia as a direct result of FeLV infection.

Cats are most likely to acquire a FeLV infection during their first year of life and/or when they have regular/continual contact with an infected cat. Kittens can get it directly from the mother either in utero or during nursing. Cats can acquire an infection from the bodily fluids of infected cats. Mutual grooming, sharing food/water bowls, sharing litter boxes or fighting are all possible means of transmission.

Fortunately, we have a new test that allows us to measure the amount of virus in a cat’s blood at a given moment in time. This test is a quantitative PCR test. This can help to initially stage the severity of an infection and to monitor the progression of the infection over time. Some cats seem to clear the virus or keep it suppressed to a point that it does not cause disease, called a regressive stage, while others develop a progressive infection that can become more severe with time.  Depending on the cat’s immune system, they can alternate between these two stages over time.  


Avoidance is the most important first step to prevent infection. If a cat is considered to be at a higher risk of coming into contact with infected cats, then the FeLV vaccine should be considered. As with any vaccine, it is not 100% protective.

Cats that test positive for FeLV should have a good relationship with their veterinarian. They should have regular visits at least two to three times annually for a thorough physical exam and possible lab work to catch any clinical signs early when they are more easily treated. 

In the past, many shelters would consider FeLV reason to euthanize. However, with current advances in testing and monitoring of FeLV positive cats, we now know that many can live a long and healthy life with this virus.

FeLV is diagnosed via blood test. For most accurate results, cats should be tested at 6 months of age or older. Pet Alliance of Greater Orlando tests all cats of age upon intake into our shelters.