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FELINE IMMUNODEFICIENCY VIRUS (FIV)

What is feline immunodeficiency virus (FIV)?
Virologists classify feline immunodeficiency virus (FIV) as a lentivirus (or "slow virus"), along with the viruses that cause progressive pneumonia in sheep, infectious anemia in horses, arthritis-encephalitis in goats, and acquired immunodeficiency syndrome (AIDS) in human beings. FIV often cause similar types of disease.

How prevalent is the infection?
FIV-infected cats are found worldwide, but the prevalence of infection depends on geographic locale and the population of cats tested. In the United States, approximately 1.5 to 3% of healthy cats are infected with FIV. Infection rates rise significantly in cats that are sick; up to 15% of cats with clinical signs of other disease also are infected with FIV. Free-roaming male cats -- especially aggressive ones -- are the most frequently infected, while cats housed exclusively indoors are much less likely to be infected.

How does the virus affect the cat?
Following initial infection, the virus is carried to regional lymph nodes, where it may replicate in white blood cells known as T-lymphocytes. The virus then spreads to lymph nodes throughout the body, resulting in a generalized enlargement of the nodes. This stage of the disease usually passes unnoticed by an owner unless the nodes are greatly enlarged. Some time later -- perhaps days but usually weeks to months -- the cat may develop a fever and a drop in the white blood cell count . This decrease in white cells is due primarily to a lack of neutrophils, the white blood cells that help protect cats against bacterial infections, and to a loss of certain types of lymphocytes called T-helper cells, which play an important role in almost every aspect of immune protection. Anemia (or low red blood cell count ) also may develop, especially later in the disease.

Persistently infected cats may appear normal for years. Eventually, signs of immunodeficiency begin to develop, and the cat's ability to protect itself against infection is compromised. The same bacteria, viruses, protozoa, and fungi that are found in cats' everyday environment -- where they usually do not affect healthy animals -- can cause severe illness in cats with weakened immune systems. These secondary infections are responsible for most of the clinical signs associated with FIV infection, and are the major cause of death in FIV-positive cats.

What are the signs of the disease?
Clinical signs of the advanced immunodeficiency syndrome appear throughout the body. Poor coat condition and persistent fever with a loss of appetite are commonly seen. Infection and inflammation of the gums (gingivitis) and mouth (stomatitis) are present in about half of the cats infected with FIV. Chronic or recurrent infections of the skin, urinary bladder, and upper respiratory tract are often present. Persistent diarrhea can be a problem. Inflammation of the tissues of the eye occurs frequently, but in most cats the damage is not clinically apparent. Slow but progressive weight loss also is common, followed by severe wasting late in the disease process. Some FIV-infected cats have recurrent illness interspersed with periods of relative health between episodes. In those cases, low white blood cell counts and anemia also appear to cycle, with episodes of low cell counts followed by recovery to nearly normal levels. However, the overall trend seems to be progressive, with cell counts dropping lower with each subsequent episode.

What can be done if my cat is infected with FIV?
One of the most important things you can do is to protect your cat from exposure to the infectious agents that cause severe disease and death in immunosuppressed animals. Keep your cat strictly indoors and away from other cats, not only to protect your cat, but also to prevent transmission of FIV to other cats as well. The use of antimicrobial drugs to control bacterial and fungal infections may be moderately successful but must be continued for long periods, or reinstituted as new infections occur. Supportive care, including intravenous fluids, and feeding of high-caloric dietary supplements, is frequently required. The use of corticosteroids or other anti-inflammatory drugs may be indicated in some cases to control gingivitis and stomatitis. Anabolic steroids may help to combat weight loss and wasting. Keep in mind that these measures are not directed at combating the virus itself. Some of the drugs useful in therapy for AIDS patients may also have the potential against FIV, but they are expensive and difficult to obtain, and side-effects appear to be greater in cats than in humans. Drugs designed to enhance or modify the immune system might be of benefit in treating FIV infections. However, most potentially effective treatments are still in the experimental stages of development and testing. Even these drugs only suppress the effects of the virus and do not destroy it.

I just discovered that one of my cats is infected with FIV, yet I have other cats as well. What do I do now?

Cat-to-cat transmission of FIV in multiple-cat households where there is no fighting among cats appears to be quite uncommon. Many FIV-positive cats are not diagnosed until after they have lived in the multicat environment for years. Ideally, any infected cats in such households should be separated from the non-infected ones, but in reality, if fighting or rough play is not taking place, the risk to the non-infected cats appears to be low.

How long can I expect my FIV-positive cat to live?
It is impossible to accurately predict the life expectancy of a cat infected with FIV. Under ideal conditions, such as isolation of the FIV-infected cat from other cats, many cats will remain in apparent good health for many years after the initial infection. If your cat has already had one or more severe illnesses as a result of FIV infection, or if persistent fever and weight loss are present, a much shorter survival time can be expected.

Can I become infected with FIV from an infected cat?
No, almost certainly not. Although FIV is structurally similar to HIV (the human immunodeficiency virus) and causes a disease in cats similar to AIDS in humans, it is a highly species-specific agent and affects only felines. In several studies, veterinarians, owners, and researchers who have had close contact with FIV-infected cats have shown absolutely no evidence of infection. Based on current evidence, it appears that FIV infections are restricted solely to cats.