Vet Blog

Understanding Feline Leukemia Virus

December 31, 2018

Common Questions and Answers About Feline Leukemia Virus (FeLV) and Feline Immunodeficiency Virus (FIV)
Michael Stephan, D.V.M.
Juno Beach Animal Hospital

What are FeLV and FIV?

FeLV is the number one cause of cancer among cats, but it can also cause a variety of blood disorders or weaken a cats immune system making it susceptible to other serious infections. Infection with the Feline Immunodeficiency Virus (FIV) leads to the development of Acquired Immunodeficiency Syndrome (AIDS) in much the same way that HIV infection in people causes AIDS. It is important to understand that both of these viruses are limited to cats and pose no known threat to humans. It is estimated that three to five percent of cats in the United States carry one of the viruses. The number of infected cats varies from region to region.

How do the viruses spread?

FeLV and FIV viruses are both spread directly from cat to cat through close, intimate contact involving transfer of blood, saliva, or other body fluids from an infected cat to a susceptible cat. This most commonly occurs through bite wounds or breeding, but may also occur by cross grooming. Both viruses are very fragile and do not survive well out of the body so infection through litter boxes, food bowls, or common surface contact poses very low threats. Kittens born to infected mothers may also acquire the infection at birth or while nursing.

How will I know if my cat is infected?

Most cats show no signs of illness in the early stages of infection with either virus. A minority of cats will show an acute illness characterized by fever and lethargy. Most cats will recover from this initial illness and appear to be normal. About five percent of cats actually clear the virus from their system at this point, but the remaining ninety-five percent harbor the virus in their bone marrow. Depending on the individual cat, weeks to years may pass before the virus becomes active again. When the virus becomes active again most cats will show vague signs of illness: loss of appetite, slow but progressive weight loss, followed by severe wasting late in the disease process, poor coat condition, enlarged lymph nodes, persistent fever, pale gums and other mucus membranes, inflammation of the gums (gingivitis) and mouth (stomatitis), infections of the skin, urinary bladder, and upper respiratory tract, persistent diarrhea. Initially, these symptoms may resolve with treatment, but they will usually return.

Are there drugs to cure FeLv or FIV?

At the present time, there are no known cures for either infection. There are drugs that will help boost the immune system and infected cats are living longer and healthier lives than they did ten years ago. It is important to remember that infected cats, even those that appear to be healthy, act as a source of infection for other cats.

How can I keep my cat from becoming infected?

The best way to prevent infection is to avoid contact with infected cats. Any new cat entering your household should be tested. A simple blood test by your veterinarian can determine the status of your cat.

Are there vaccines available to protect my cat?

There are vaccines available against both FeLV and FIV, however, their use is controversial. The vaccine for FeLV is thought to be effective in about eighty percent of the cat population. The remaining twenty percent of cats will not develop protective immunity from the vaccine. The American Association of Feline Practitioners (AAFP) recommends the vaccine only be used in young cats at significant risk of encountering the virus and not at all in cats greater than four months old with minimal to no risk of exposure to infected cats.

There are five different strains of FIV virus in the United States. The vaccines available at present cover only two of these strains and, like the vaccines for FeLV, they are not 100 percent effective. Unfortunately, cats who are vaccinated for FIV will test positive for the disease on all commercially available tests. This makes it impossible to distinguish a vaccinated cat from an infected cat. At the present time the AAFP does not recommend the use of the FIV vaccine.

The best way to prevent infection in your cats is to minimize their exposure to infected cats. As much as possible, your cat should be confined to the indoors. A secure screened enclosure can provide access to the outdoors with minimal risk of infection. All new cats should be tested before being introduced to cats in the household.

Universities and vaccine manufacturers devote large sums of money to research on FeLV and FIV, so our understanding of these awful diseases is constantly changing. There is no one program of vaccination that will fit every cat or every cat owner. You should discuss your cats lifestyle with your veterinarian and develop a vaccination program for your cat which will help ensure a long, healthy life.