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Feline Immunodeficiency Virus

The feline immunodeficiency virus (FIV), first discovered in a northern California cattery in 1986, is a major cause of chronic immunodeficiency in cats. FIV is a retrovirus belonging to the lentivirus family. It is related to the HIV virus in humans (the virus that causes AIDS). However, these two viruses are species-specific. HIV does not produce disease in cats and FIV does not produce disease in humans.

FIV infection is believed to be transmitted by cat bites, such as the one causing this infected wound.

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Although its exact incidence has yet to be determined, FIV has been found in cats throughout the United States and is believed to affect 2 to 4 percent of cats in the general population. The incidence is highest in outdoor cats and in males 3 to 5 years of age. This suggests that cat bites, occurring during fights among toms, are a source of virus transmission, especially since the virus is shed in saliva.

Close or casual contact alone is not a major mode of transmission. There is no evidence that the disease is transmitted by mating. However, if a queen becomes infected while pregnant, she may pass the virus on to her unborn kittens.

Signs of Illness

Four to six weeks after FIV exposure, there is acute illness characterized by fever and swelling of the lymph nodes. The white cell count is below normal. The cat may have diarrhea, skin infections, and anemia. After the acute infection, there is a latent period from several months up to 12 years during which the cat appears to be healthy. Eventually, signs of a chronic immunodeficiency syndrome appear and progress slowly (again, over a period of months or years).

Cats with chronic FIV infection present with a variety of unexplained signs of ill health, including severe mouth and gum disease, long-standing diarrhea, loss of appetite and weight with emaciation, fever, recurrent upper respiratory infections with eye and nasal discharge, ear canal infections, and recurrent urinary tract infections. These signs are similar to those associated with other immunodeficiency disorders, such as feline leukemia, severe malnutrition, immunosuppressive drug therapy, and widespread cancer. About 50 percent will have chronic oral conditions and about 30 percent will have chronic upper respiratory infections. Ten to 20 percent will have diarrhea. Many will show neurological signs such as dementia. FIV-infected cats also are much more likely to develop lymphoma.

Diagnosing FIV

If antibodies to FIV are found in the cat’s serum using an ELISA test, it can be assumed that the cat is persistently viremic and can be a source of infection to other cats, or has been vaccinated with the FIV vaccine. All ELISA-positive tests should be confirmed with another test, such as an IFA or Western blot immunoassay, performed at a reference laboratory. However, even these tests cannot distinguish vaccinated cats from infected cats. Research continues for a test that will distinguish between truly infected cats and cats who have been vaccinated.

There are two sets of circumstances in which these tests may have a false negative result. One is during the terminal stages of FIV when the cat is unable to produce detectable antibodies. The other is during the early stages when virus is present in the serum but antibodies have not yet been produced. In the latter case, the cat can be retested in two to three months.

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