Feline Immunodeficiency Virus (FIV)

Apr 12, 2018

Feline Immunodeficiency Virus (FIV) is a virus that causes a weak immune system in cats. While the virus is similar to HIV/AIDS in humans, the disease is less severe and is rarely life threatening. It was identified first in the United States in the mid-1980s and affects cats worldwide.


FIV infection results in depression of the cat's immune system, allowing the cat to become ill from infections that it could normally eliminate. Clinical signs of FIV infection are very diverse because signs frequently involve a variety of secondary infections.

Most infected cats show no clinical signs of the infection, so testing is an important aspect of population disease control. After initial infection, many cats show a brief period of transient lethargy, fever, and swollen lymph nodes that may easily be missed by owners and veterinarians. After this, many cats can live their whole life with the virus, while others may show no signs for four to five years, then go on to develop signs of illness when the immune system is affected.

Cats with FIV-associated disease may look completely normal, while others may have a poor hair coat, chronic fever, decreased appetite, chronic gum and mouth infections, persistent diarrhea, slow progressive weight loss, and many other signs. While rare, the virus can affect the nervous system as well, entering the fluid cushion (cerebrospinal fluid) that surrounds the brain and spinal cord, leading to nervous system signs. It typically takes years for signs of serious illness to develop. True “feline AIDS” (a drop in white blood cells associated with a high risk of death) is a very rare syndrome. These signs of illness may also persist for years, with periods of good health between episodes.

The average lifespan of a cat infected with FIV is not significantly different from that of an unaffected cat. While FIV positive cats may need more aggressive care for some illnesses and may be more prone to infections, they generally do not require regular medications.  


The virus is usually spread in the saliva or blood from one cat to another via cat bites, so the disease is most common in roaming, fighting males. The average age of infection occurs when the cats are in young adulthood, around three to six years of age. Bites must be deep enough to draw blood, and so disease transmission risk is low between indoor cats who get along well. 

Cats cannot give feline immunodeficiency disease to people, nor can cats develop human AIDS. Studies indicate that veterinarians, owners, and researchers who have had close contact with FIV-infected cats show no evidence of disease.

The virus does not live long outside the cat, so it is close contact with other cats that provides a means of transmission between cats. If a queen (intact female cat) gets FIV while pregnant, she can pass it to the developing babies (foetuses) in the uterus.

There is no cure for FIV. The use of antibiotics and supportive care may control the secondary infections as they occur, but nothing can cure the FIV infection itself.


Have your cat tested if you are concerned she may have been exposed to this virus. FIV infection is usually diagnosed by a blood test called an ELISA. A second test (Western Blot or PCR) may be recommended if the initial screening test is positive in order to confirm infection. It is often prudent to test for Feline Leukemia Virus at the same time; many screening panels contain both virus tests. If you are going to adopt a stray cat, make sure you get a blood test before introducing the new cat to your home. Note that immature cats (less than six months old) can have a false positive test due to antibodies from their mother; so if a young cat tests positive, another test is done after six months of age to ensure it is a true infection and not residual antibodies from the mother cat.


A cat with FIV infection should be kept indoors and away from other cats it may fight with to help prevent spread of the disease. Cats are less able to fend for themselves when ill and may be injured more easily than healthy cats.

Vaccination is not widely used in North America, and is not readily available to most veterinarians. The vaccine will make a cat test falsely positive on some tests, and so diagnosis after vaccination can be difficult. While the vaccine is more effective on strains of virus found in other parts of the world, it does not work as well on North American strains.

Quarantine any new additions to the household, and test them before bringing them into a home or facility. Reduce stress and crowding, and provide quality nutrition and appropriate preventive health care including twice yearly or more frequent health assessments for sick cats, as per your veterinarian’s instructions. Avoid breeding cats that test positive for the virus.

Use appropriate disinfection to clean an environment that has had an infected cat resident before introducing new cats or kittens; since the virus survives poorly outside of the cat, it is necessary to remove germs shed into the environment from associated infections such as pus from skin or dental infections. Basic soap and water and any household cleaner will effectively kill this virus.


There is no cure for the FIV infection. Newer trials suggest antiviral medications (similar to the medications used to treat AIDS in humans), interferon therapy, and other immunomodulatory drugs show some promise for chronic management of disease associated with viral infection. Supportive care is provided for complications associated with disease such as secondary infections, stomatitis (deep gum inflammation), or encephalitis (inflammation of the brain).

Talk to your veterinary healthcare team for more information about FIV infection and related immune system compromise.

Kathleen Cavanagh, BSc DVM MET
Consulting Online Editor CVMA

Matthew Kornya, BSc, DVM, Resident ABVP
Consulting Editor                                                                 

Jan 24, 2018