The name, Feline Leukemia virus, or FeLV, confuses many people. In humans, leukemia refers only to a type of cancer affecting the white blood cells. FeLV virus only affects cats, and very rarely causes actual leukemia, or cancer of the white blood cells. FeLV most commonly causes immune suppression, anemia or other types of cancers and it often leads to death within three years of diagnosis. Symptoms are quite variable, depending on the stage of infection and strength of the cat’s immune system. Some infected cats will appear healthy, while others may have secondary respiratory infections, weakness, fever, labored breathing or neurological signs.
Cats are most susceptible when they are young. FeLV is very contagious, but does not live long in the environment. This virus is spread from mothers to kittens or by close affectionate contact such as mutual grooming, sharing bowls and litter boxes—I tell my students that “Leukemia is for Lovers.” However, bite wounds are an important method of transmission as well.
What is Feline Immunodeficiency virus and what are the symptoms?
Feline Immunodeficiency virus, or FIV, is spread primarily by fighting, so it is most commonly seen in outdoor cats and intact cats. FIV affects white blood cells primarily, leading to immunosuppression and increased susceptibility to infection, dental disease and an increased risk of certain cancers. However, FIV may have an asymptomatic period of many years, before cats show signs of disease. This means that many infected cats lead normal lives, especially with good care.
What are the specific updates to the previous guidelines?
- The incidence of both diseases in the U.S. is around 3 percent and has not significantly changed since publication of the previous guidelines.
- Salivary RNA testing is now available for FeLV, but is of limited use due to poor sensitivity. The point-of-care antigen (viral surface particle) test remains the most reliable for screening.
- Cats infected with FeLV have more natural ability to eliminate the virus than we previously thought. We do not know how much mere exposure to the FeLV virus contributes to problems later in life.
- There are still no effective treatments for either disease.
How are Feline Leukemia and Immunodeficiency viruses detected?
There are fast, accurate in-clinic tests for both diseases. It is important to remember that any test is only one snapshot in time. Both diseases have incubation periods during which detection is difficult. Negative results should be repeated if the cat has a recent risk of exposure. Alternatively, false positive results may occur, especially in populations of cats at low risk of disease, such as single, indoor cats. Positive results should be confirmed, especially if the cat does not fit the clinical picture of the disease.
The FIV test detects antibodies which are produced by exposure to the virus. False positives can occur in cats vaccinated for FIV and in kittens from infected mothers. FIV-test-positive kittens should be retested at 6 months of age, as they should no longer have antibodies from their mothers at that age.
How can pet owners protect their cats against these viruses?
Number one is to prevent exposure. Keep cats indoors and test any cat prior to introduction into the home. Neutering outdoor cats lessens fighting and roaming behaviors, and therefore lessens the risk of infection. Good preventative care—such as check-ups, vaccinations, parasite prevention and good nutrition—helps to keep cats healthier and less susceptible to infection.
Safe, effective vaccinations are available for FeLV. All kittens should receive vaccinations for FeLV because they are at the most vulnerable age for infection, and it is difficult to predict the future lifestyle of a cat. Vaccination of adult cats depends upon risk of exposure. Indoor cats without exposure to other cats may not need vaccination. At-risk adult cats may be vaccinated every one to three years depending on the level of exposure and brand of vaccination used. This vaccine does not interfere with test results.
However, the vaccine for FIV is no longer available in the U.S. It caused false positive results on routine testing and did not provide many protective advantages.