Feline Immunodeficiency Virus (FIV)

Feline immunodeficiency virus is a lentivirus that affects cats worldwide. FIV is the only non-primate lentivirus to cause an AIDS-like syndrome, but it is not typically fatal for cats. FIV can attack the immune system of cats, much like the human immunodeficiency virus (HIV) can attack the immune system of human beings. Infected cats can live as carriers and transmitters of the disease for many years, but the infection can eventually lead to destruction of the immune system and exhaustion of certain white blood cells. While a preventive vaccine is available, its effectiveness is not yet universally accepted among veterinarians.  Currently, there is no known cure.

Disease Stages and Symptoms

FIV progresses through similar stages to HIV in humans. The initial stage, or acute phase, is accompanied by mild symptoms such as fever, lethargy, anorexia (loss of appetite) and lymphadenopathy (swollen lymph nodes). This initial stage is fairly short and is followed by the asymptomatic stage. Here the cat demonstrates no noticeable symptoms for a variable length of time. Some cats stay in this latent stage for only a few months, but for some it can last for years. Factors that influence the length of the asymptomatic stage include the strain and subtype of the infecting virus, the age of the cat and exposure to other pathogens. Finally the cat progresses into the final stage known as the feline acquired immunodeficiency syndrome (FAIDS) stage where the cat is extremely susceptible to secondary diseases, which inevitably are the cause of death.


FIV primarily spreads through deep bite wounds and scratches, where the infected cat’s saliva enters the other cat’s bloodstream, such as those incurred during territorial battles between males. Cats housed exclusively indoors are much less likely to be infected, provided they do not come in contact with infected cats. In some cases, however, casual contact cannot be ruled out as a potential mode of transmission. FIV may also be transmitted from pregnant female cats to their kittens in utero. FIV is a feline disease and there is no credible evidence of transmission to dogs or humans.


Your veterinarian will check your cat’s history, look for clinical signs, and possibly administer a blood test for FIV antibodies. FIV affects 2-3% of cats in the US and testing is simple.  False positives may occur when the cat carries the antibody (which is harmless), but does not carry the actual virus. The most frequent occurrence of this is when kittens are tested after ingesting the antibodies from mother’s milk, and when testing cats that have been previously vaccinated for FIV. For this reason, neither kittens younger than 8 weeks nor cats that have been previously vaccinated are generally tested.  Kittens and young cats that test positive for the FIV antibody may test negative at a later time, provided they have never been actually infected with FIV and have never been immunized with the FIV vaccine.

Unless there is some other evidence, testing of strays or adopted cats is generally inconclusive, since it is impossible to know whether or not they have been vaccinated in the past.  Some veterinarians recommend humane euthanasia of stray cats that test positive because of the risk of transmission, especially if there is a chance that those strays would be adopted into a household with healthy cats or escape back into the streets.

Tests can be performed by your veterinarian with results obtained within minutes, allowing for a quick consultation. Early detection helps maintain the cat’s health and prevents spreading infection to other cats. With proper care, infected cats can live long and healthy lives.