Feline Immunodeficiency Virus or FIV

Filed Under: Cats, Diseases

Feline Immunodeficiency Virus or FIV is a lentivirus that infects domestic cats and cheetahs. FIV is the cause of feline AIDS but is not the same virus as Human Immunodeficiency Virus (HIV), the cause of human AIDS.

The prevalence of FIV in domestic cats in North America is estimated to be at a 6% level regardless of whether the cat is owned or feral.

Approximately 15% of cats that test positive for Feline Leukemia (FeLV) also test positive for FIV.

FIV was first described in 1986 in a population of cats showing clinical signs of an immunodeficiency. There are five subtypes of the virus based on genetic variation. The virus is worldwide in distribution. The predominate subtypes in the United States are A and B.

The virus is shed primarily in saliva. Transmission is primarily through bite wounds from infected cats. Young unaltered adult males are at greatest risk from infection due to fighting. The spread of FIV through water bowls or grooming is unlikely. Vertical transmission is rare but considered possible.

Antibody tests are usually recommended for screening. These tests are commercially available and are easily conducted in most veterinary clinics. Antibody tests may be complicated to interpret in kittens that have acquired FIV antibodies by passive antibody transfer in colostrum either by vaccination or infection. Maternal antibody wanes by three to six months of age and the kitten eventually becomes negative on antibody testing. False negatives may occur because not all infected cats will produce antibodies to FIV. Virus culture is extremely accurate but is not commercially available.

Currently there is only one vaccine available for the prevention of FIV in the United States and Canada. The vaccine is manufactured by Fort Dodge Animal Health. The Feline Advisory Panel considers FIV vaccination a noncore vaccine and suggests its use be restricted to cats at high risk of exposure. Cats at high risk of exposure include outdoor cats and cats not infected with FIV that are living with FIV-infected cats. Prior to vaccination cats should be antibody tested and shown to be negative. Cats undergoing vaccination will produce antibody which will be undistinguishable from antibody produced secondary to FIV infection on commercially available tests. Due to FIV antibody positive testing following vaccination, it is recommended that vaccinated cats be microchipped to help clarify vaccination status should the pet become lost and taken to a shelter. A well meaning shelter that tests for FIV antibody may mistakenly euthanize a vaccinated cat when they screen for FIV and obtain a positive antibody test. Kittens eight weeks and older may be vaccinated. An initial series of three doses of vaccine are administered at three week intervals. Annual revaccination is recommended when there is risk of infection.

Initial clinical signs of infection include an elevated temperature, swollen lymph nodes, loss of appetite, diarrhea, and lethargy. There will also be a decrease in white blood cell numbers. Typically the cat will recover from initial infection and appear normal for months to years until immunodeficiency ensues. When immunosuppression occurs, secondary opportunistic infections of the respiratory system, GI tract, eyes, urinary tract, skin, mouth and gums will occur. These cats have a higher than expected incidence of certain tumors and tend to lose weight. Neurologic clinical signs may be seen in 5% of infected cats and will be seen clinically as behavioral abnormalities. These abnormalities may include dementia, convulsions, and psychomotor disturbances. Eventually the cat’s immune system may become too weak to fight off other infections or diseases. As a result, the cat will eventually succumb to one of the secondary infections.

Cats remain infected for life. There is no treatment or cure for an FIV infected cat.

Various ways to avoid FIV infection:

  • Vaccination
  • Limiting the exposure of your cat to free roaming outdoor cats
  • Have new cats tested before introducing them into a multi-cat household
  • Isolating an aggressive cat from other cats


“The 2006 American Association of Feline Practitioners Feline Vaccine Advisory Panel Report”. Journal of the American Veterinary Medical Association, Vol 229, No. 9, November 1, 2006. pp. 1405-1439.

Kahn, Cynthia Editor. The Merck Veterinary Manual. 9th Edition 2005. pp661-662

Topics: AIDS, bites, FIV

Symptoms: diarrhea, fever, lethargy, loss of appetite

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