Feline leukemia and
feline immunodeficiency virus

By Dr. Steve Ting, DVM

Feline leukemia virus (FeLV), first identified in 1964, causes a suppression of the immune system similar to AIDS. This leaves the cat open to a wide variety of secondary infections. The disease caused by FeLV is commonly called feline leukemia. It is estimated that 2 percent to 3 percent of cats in the United States are infected with FeLV. It is seen most commonly in cats between 1 and 6 years of age. After infection with the virus most cats succumb to FeLV-related disease within 2-3 years.

Symptoms of FeLV are fever, weight loss, lethargy and many other signs. Because it suppresses the cat's immune system, FeLV leaves the body open to many infections and also makes it harder to clear up these infections. FeLV is also related to many types of cancer in cats.

In infected cats, the virus is shed in saliva, urine, tears and milk. Cat-to-cat transmission is by contact with any of these fluids by fighting, grooming, or contact with contaminated water, food or litter pans. Bite wounds are probably the most common form of transmission but prolonged close contact between cats enhances the likelihood of transmission.

There is a vaccine for FeLV. There have been many studies done on the vaccine's effectiveness and it is reported to be between 20% and 80% effective. The best way to prevent your cat from getting FeLV is keeping it from being exposed to cats who may be carriers or to contaminated items.

Feline immunodeficiency virus (FIV) is closely related to the human AIDS virus and just like FeLV it suppresses the cat's immune system. The disease caused by FIV is commonly called Feline AIDS. It is estimated that 1.5% to 3% of cats are infected with FIV. It is most commonly seen in young male cats. Male cats are three times more likely to get FIV than females. Free roaming cats are much more likely to get infected. Cats can have the virus for years before showing any symptoms of disease. There can also be asymptomatic carriers.

Symptoms are very similar to FeLV. Cats often will have recurrent illnesses with periods of relative health between episodes; however, the general trend tends to be progressive. Most cats succumb to illness within one year after starting to show sickness.

The major mode of transmission for FIV is through bite wounds. Transmission through casual contact is not common. Therefore cats in the same household with an FIV positive cat are not as likely to get FIV as they would be if this same cat had FeLV.

Unfortunately, at the current time no vaccine is available for FIV.

I hope this clarifies some of the differences between these two viruses.