Feline immunodeficiency virus (FIV) is a virus that results in immunosuppression - suppression of an animal's immune system response. Immunosuppression weakens the body's defense and leaves an animal vulnerable to infection, so FIV-infected cats are predisposed to a wide array of debilitating infections.

A FIV infection has three stages. The first stage can include a fever, a decreased white blood cell count, and enlarged lymph nodes, which an owner may not even notice. During the second stage the cat can remain healthy for several years. The third chronic stage is characterized by a range of clinical disorders and infections that can include inflammation of the mouth and gums, chronic respiratory infections, persistent diarrhea, ongoing bladder and kidney infections, and chronic skin disease to name a few. Eventually, the cat's immune system is so weakened it can no longer protect the cat, and the animal dies.

Although contagious, FIV is fortunately not transmitted as readily as the feline leukemia virus. The most common mode of FIV transmission is through a bite wound. So cats with the highest prevalence of FIV are those most likely to get wounds -- free-roaming, unneutered males prone to fight in territorial disputes. Strictly indoor cats are not at risk unless they come in contact with an infected cat.

There is no effective "cure" for FIV. However, there are steps that can be taken to support an infected cat and help relieve the symptoms of chronic infection. Remember, FIV has a relatively long incubation period and a recently diagnosed asymptomatic cat may have several disease-free years to enjoy. Your veterinarian will discuss with you the appropriate methods of care if your cat is FIV-infected.

Although considerable research is under way, there is no vaccine available for FIV. For now the best method of prevention is to keep your cat away from high-risk groups such as free-roaming, unneutered males. It is also a good idea to have a cat tested for FIV if you are considering adoption and you do not know the cat's history.

As a note of interest, although FIV and human immunodeficiency virus (IIIV) - the virus responsible for AIDS in humans - belong to the same subfamily of viruses and can cause common clinical disorders, FIV and HIV are not the same virus. They are two distinct species specific viruses. You cannot get AIDS from your FIV-infected cat. Nor can cats get AIDS from humans. Likewise, there is no evidence that FIV infects any species other than cats.

The writers are Dr. Steven B. Holzman, Dr. William R. Haagenson and Dr. Kathleen Tapley. They are associated with the Nassau-Suffolk Veterinary Hospital of Farmingdale.