Feline Leukemia Virus

Louis N. Gotthelf, DVM
Animal Hospital of Montgomery, LLC
Montgomery, AL 36109

Feline leukemia virus (FeLV) has been found in free roaming cats for many years. In the pet cat population, it is estimated that somewhere between 3% and 14% of cats are infected with this virus.

The virus is found primarily in the saliva of infected cats, but it can also be recovered from the milk, tears, and urine. Transmission of the virus most often occurs at birth when the infected queen bites the umbilicus seeding the blood with viruses from her saliva. The virus infects kittens and it often settles in the bone marrow where it makes it hard for the bone marrow cells to produce red blood cells. Kittens with active infection are often weak and pale from anemia. Over a period of time, many of them require blood transfusions to keep them alive. Older outdoor cats that fight are often infected by the saliva of the aggressor. These are the cats that become infected carriers and become immune suppressed. FeLV infected kittens and older cats get sicker more often than normal cats from the so called FeLV associated diseases. These include lymphoma, leukemia, anemia, and infectious viruses.

Infection with the virus does not always mean disease and it does not mean immediate euthanasia! Over half of infected cats that recover from their infection are non-symptomatic carriers of the virus, but they do not get sick from it. They can live long, normal lives, but they should be isolated from exposure to other cats and kittens. Others cats that have the infection have a decreased immune system function that makes them more susceptible to other viral and bacterial diseases as well as rendering them less able to heal themselves when injured. These cats also become carriers of the virus in their secretions and are capable of infecting other cats. Cats with active FeLV infection causing disease rarely live more than 3 years.

At Animal Hospital of Montgomery, we recommend testing all kittens that are age 2 months and older for Feline Leukemia Virus (FeLV). It can take as long as 60 days for the test to show positive after infection with the Feline Leukemia Virus. Cats and kittens that are feral should always be tested to make sure that they are not bringing this virus into the home where other non-infected cats live. Any cat that is exposed to a possibly infected cat with FeLV should be tested. This is a simple blood test that we can do right in our office in about 8 minutes.

If kittens test negative for the virus, we recommend vaccinating them against FeLV if they will ever go outside or if they will ever be exposed to a FeLV infected cat. The vaccine is given in 2 shots spaced about 3 weeks apart, then once annually. Older cats testing negative will be given one shot every year.

We occasionally see a vaccinated cat that shows all of the signs of Feline Leukemia. For those cats that do not have Feline Leukemia Virus detectable from their blood test, we will often test their bone marrow to see if they have virus hidden there. About 10% of cats that are infected with FeLV will have negative blood tests, but positive bone marrow tests.