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The Feline Leukemia Virus (FeLV) and the Feline Immunodeficiency Virus (FIV) By Frank Utchen, DVM
General

Two of the most devastating viral diseases for cats are Feline Leukemia and Feline AIDS. Each is caused by a virus for which there is no cure once a cat contracts it. Both viruses are in the family of viruses called Retroviruses, which puts them in the same group as the Human Immunodeficiency Virus. Fortunately, repeated studies of veterinarians who routinely come in contact with these diseases, and repeated unsuccessful attempts to grow these viruses in human cell cultures has confirmed that neither virus is transmissible to humans.

For cats, these viruses are both spread by bite wounds, as the virus is secreted from a cat's body into their saliva. As opposed to HIV, the Feline Immunodeficiency Virus is not a sexually transmitted disease. Therefore, even spayed and neutered cats can contract feline AIDS without the precondition of having mated with another cat.

These viral diseases have the same biological behavior in cats as HIV does in humans. Initially, there is no indication that a cat has become infected. Any cat with a bite wound from another cat may have been exposed to either virus. In the case of the Leukemia virus, some cats will mount an immune response and fight off the virus immediately after exposure. However, the majority will not do so and will remain carriers of this deadly pathogen. Cats that are exposed to the Feline Immunodeficiency Virus always become carriers for life.

Most studies indicate that approximately 40% of cats exposed to FeLV will fight off the virus, but the remaining 60% will remain infected and die within 3 years. A small percentage will live longer. With FIV, the average time to the onset of disease after a cat contracts the virus is much longer—approximately 10 years.  With either virus the primary problem that develops is the same: the immune system begins to fail, with consequences for a cat similar to those for people whose HIV infection has progressed to the clinical disease of AIDS. Eventually, almost all cats with either virus succumb to secondary bacterial infections and other diseases. In some cases, cats with the Leukemia Virus will in fact develop the cancer of leukemia (hence the moniker).

Research into possible treatments for these diseases has largely been unsuccessful. There are reports that indicate the use of Interferon as an oral medication given daily can help maintain a cat's immune function and thereby delay the onset of secondary infections. This has not been documented by controlled studies.

The use of anti-viral drugs such as AZT used to treat AIDS has been documented to be helpful, but is expensive and impractical for routine use in cats. At present, it is considered that there is no cure for either of these diseases.

There is an effective immunization against the Feline Leukemia Virus, although none exists for FIV. (An immunization against FIV has been developed and marketed by one pharmaceutical company, although the American Veterinary Medical Association, the American Association of Feline Practitioners and most veterinarians and veterinary immunologists recommend against its use due to lack of data indicating efficacy).

Once it is known that a cat is a carrier of either virus, that cat should be kept indoors thereafter to prevent it from interacting with other cats outdoors. This eliminates the risk of transmitting the virus(es) to unknown cats outdoors, and helps reduce the risk of secondary infections to the known carrier.   If a cat is confirmed as a carrier of the Feline Leukemia Virus and is to be kept indoors, all other cats in the house should be immunized against that virus.

If a cat is confirmed as a carrier of FIV, there are no protective medical steps than can be taken to reduce the risk of transmission to other cats in the household, apart from isolating the cats from each other. Although FIV can only be transmitted through a bite wound contaminated by saliva, it has been postulated that there is about a 5% chance each year that a cat will contract FIV from another cat even without a bite wound. Whether this is because there are unknown incidents of biting, or transmission occurs through other contact with a carrier cat's saliva, is not known.

Veterinarians generally recommend all new kittens and cats have a blood test done to determine their status for these infections. Only cats that go outdoors are at risk for contracting these infections, so at our practice we do not recommend that indoor cats be immunized against the Leukemia Virus. If a cat is to go outdoors also, it should be immunized against the Leukemia Virus by receiving a series of two injections about three weeks apart, followed by a booster shot a year later, and then a booster every 3  years after that. Again, there are not preventive measures that can be taken to avoid FIV infection if a cat goes outdoors and encounters other cats. By testing your kitten for these infections we can begin to control the spread of these deadly viruses, and guarantee your kitten and other cats you may already have, all have as healthy a life as possible.

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