Feline Immunodeficiency Virus (FIV) is in the same family, Retroviridae, as Feline Leukemia Virus (FeLV). Therefore, they share certain characteristics, such as the ability to suppress a cat’s immune system and to initiate and allow the growth and spread of cancer. The virus was discovered in 1986.
FIV is known as the virus of unfriendly cats. It is most commonly transmitted by the bite of an infected cat, as high levels of the virus are present in saliva. Fighting among outdoor cats is a very common practice and leads to sometimes-fatal bacterial infections in abscesses as well as FeLV and FIV transmission. Deep bites deposit the virus into tissues that can incubate the virus and present it to the immune system for replication (reproduction of the virus) and spread throughout the body.
Shortly after initial infection the cat becomes ill, but this is often a mild illness that may be missed by cat owners. If the bite wound is also infected by oral bacteria from the neighborhood bully, signs of illness may be attributed to that.
The Rest Of The Story, however, is not all bad.
Indeed, cats infected with FIV may not become ill for years. Still, in the background, damage is being done to the immune system that will set the stage for an eventual downfall.
There are two main functional parts of the immune system, cell-mediated immunity (CMI) and humoral immunity. Cell-mediated immunity, as its name implies, uses various cells in the body to fight infection and disease. CMI is damaged most in FIV patients, thus they tend to develop cancers, as well as infections of organisms that thrive inside cells. Being a retrovirus, FIV naturally has a strong tendency to produce cancer. On top of that, lacking a healthy CMI, some cancers escape early destruction that a strong CMI might have stopped. These facts explain why cancer is so prevalent in FIV-infected cats.
Unusual skin conditions may be seen in FIV patients. I have seen some very unusual patterns of hair loss in these cats, and the only case of Demodex felis I’ve seen in 30 years of practice was in an FIV cat whose immune system was suppressed.
Humoral immunity is based on the production of antibodies that circulate in the bloodstream. As long as strong humoral immunity persists, diseases that antibodies can kill are not experienced.
While fighting is still known to be the major mode of transmission, infrequent cases are confirmed in which FIV has been transmitted among housemates even where there is no fighting and no outside exposure.
Laboratory-reared queens have been documented to transmit the virus through milk to their kittens.
Virus is frequently present in semen, and some cases of sexual intercourse transmission have occurred.
Cats who test positive for FIV must be isolated. They absolutely must be kept indoors for their own protection from disease, as well as to prevent them from exposing other cats. Ideally they should be in a one-cat household. If there are other cats in the home the FIV-infected cat must live totally separated and must not interact with the others. When leaving the room or area allotted to the FIV cat, you must thoroughly disinfect your hands and any fomites that must leave the room.
In summary, while the long-term future is not good for the cat infected with Feline Immunodeficiency Virus, cats who are kept isolated and have their preventive health care properly managed can live for a surprisingly long time with their disease.
MyPetsDoctor.com expresses our gratitude to Dr. Julie Levy and her associates who published much of this information in The Journal of Feline Medicine and Surgery, 2008.MMFIV