Feline leukemia virus (FeLV) is classified as a retrovirus because it permanently alters the genetic makeup of infected cats.  As a consequence, infected cats become ill from one or more chronic illnesses.  The virus is transmitted to other cats by body fluids, especially saliva and nasal secretions, and to kittens, from infected mother’s placental blood or from the mother’s milk.  Although human immunodeficiency virus (HIV) is also a retrovirus and causes similar disease in humans to that caused by FeLV in cats, FeLV does not affect humans, and HIV does not affect cats.

Incidence 
Approximately 2 to 3% of all cats have FeLV.  Among cats with chronic illnesses, the FeLV infection rate is more than 10%.  High risk cats for FeLV exposure are those who contact infected cats or use the same food and water dishes as infected cats.  Cats allowed outdoors and kittens born to infected mothers are also at higher than average risk for exposure.  Young cats are about 3 times more likely to become infected, if exposed to the virus, than adult cats that are exposed.

Symptoms/Signs      
When a cat is infected with FeLV, the virus can cause cancer, disrupt the normal production of blood cells (production failure or uncontrolled excess production), or suppress the immune system, allowing other infections to develop.

Diagnosis 
Blood tests can be done by your veterinarian to diagnosis FeLV in the bloodstream.  One test, called an ELISA, detects the virus in the serum and outside of cells.  An ELISA positive cat has been exposed and the virus is in the cat’s body, but it may not be able to invade cells and alter the cat’s genetic makeup.  These cats, especially if they are adults and appear healthy, may rid themselves of the virus and not develop FeLV disease, but some will become FeLV infected.    ELISA positive cats require repeated testing or to be tested by another test, called the IFA.  The IFA blood test is run on cells in the blood and detects the virus inside the cells.  If it is positive, the cat is highly likely to be permanently infected with FeLV and will eventually die of a FeLV-associated disease within days to 3 years.  Cats that are positive on either test can transmit the virus to other cats by direct contact or sharing food or water bowls.

Treatment 
There is no effective treatment for FeLV-infection.

Management
Take measures to detect or prevent transmission to other cats

• Have diagnostic tests run on all cats in the household
• Spay FeLV-infected females
• Isolate the infected cat and all other FeLV-positive cats in the household from FeLV-negative or new, untested cats
• Do not allow infected cats to roam outdoors where they may pick up secondary infections of viruses, bacteria, or parasites or transmit FeLV to other cats

Prevention

• Keep all cats indoors
• Test all new cats before introducing them to your other FeLV-negative cats
• Consider vaccinating, especially healthy young cats

For more information, contact your local veterinarian or the MU Veterinary Medical Teaching Hospital 573-882-7821 or visit www.vmth.missouri.edu.