FIV – Feline Immunodeficiency Virus

Feline immunodeficiency virus (FIV) is a retrovirus that can infect cats. FIV is almost exclusively spread through bite wounds. Experimentally, there is evidence that it can be spread sexually as well1.

TJ FIV+ ex-feral cat who lives with 6 FIV- cats indoors.

This mode of transmission means that in a stable multi-cat household where minimal to no fighting occurs, the chance that a cat infected with FIV will pass the virus along to another cat is minimal. In fact, one recent study showed “a lack of evidence of FIV transmission, despite years of exposure to naturally-infected, FIV-positive cats in a mixed household”2. (In this case, a mixed household was one in which at least one cat infected with FIV lived with other cats not infected.)

At one point, not too long ago, the recommendation for a cat that tested positive for FIV was to euthanize the cat immediately. Fortunately, because we now know much more about the virus, that recommendation is no longer the standard advice. Though FIV is a serious and likely fatal disease once a cat becomes symptomatic, infected cats can remain asymptomatic for long periods of time, sometimes for many years.

False positive results are relatively uncommon, but they do happen. A positive result in an apparently healthy cat should always be confirmed by at least one other type of test. Cats who have been vaccinated against FIV will test positive on screening tests and Western Blot tests, in which case a Polymerase Chain Reaction test is a better choice. Cats under the age of six months will sometimes erroneously test positive on FIV screening tests because they have maternal antibodies against the disease in their bloodstream.

The diagnosis of FIV remains tentative until the test can be repeated within six weeks time. That’s because a positive FIV test does not always point to a cat that will remain positive. A percentage of cats can actually clear this virus from their circulation within a few weeks. And as far as is known, these cats remain immune to FIV for life.

If you have any doubts as to your cat’s diagnosis, ask your veterinarian to show you the results of at least two different types of FIV tests and explain why he or she has reached the conclusion that your cat does indeed have FIV.

Your veterinarian may also recommend additional diagnostic tests like a complete blood cell count (CBC), blood chemistry panel, and a urinalysis to get a better picture of your cat’s overall health and to plan appropriate treatment.

  • Medications: Anti-viral drugs (e.g., AZT) can help some cats with FIV, but treatment is usually limited to supportive care and dealing with secondary health concerns as they arise.

Zidovudine (AZT) and other antiviral medications have been used to treat some cats suffering from the effects of FIV infection. These drugs can reduce a cat’s viral load, but the side effects of treatment may outweigh the benefits. Veterinarians have also used interferon on cats exhibiting symptoms associated with FIV, but the benefits of this drug are questionable.

Erythropoietin can be prescribed to raise the red blood cell count of an FIV positive cat suffering from anemia.

Secondary bacterial and fungal infections are a common problem in cats with FIV. The appropriate use of antibiotics and antifungal medications can often improve a cat’s condition for a period of time. When a cat’s quality of life declines to an unacceptable level, euthanasia or hospice care is the best option.

  • Diet: Good nutrition is essential to maintaining optimal immune function in FIV positive cats.

Many cats who test positive for FIV but are not exhibiting any symptoms of the disease can live happily for years after their diagnosis. These individuals should eat a highly nutritious diet to promote good immune function and be kept indoors to limit their exposure to infectious diseases and reduce the chances that they could spread FIV to other cats. FIV positive cats should have a physical examination, complete blood cell count, blood chemistry panel, and urinalysis performed by a veterinarian once or twice a year so any problems that do develop can be caught and addressed early.

Possible Complications to Watch For

  • Cats who take antibiotics can develop loss of appetite, vomiting, and diarrhea.
  • Antiviral medications can cause bone marrow suppression. Cats on antiviral drugs should have a complete blood cell count (CBC) checked frequently.
  • Symptoms of a worsening FIV infection vary but often include oral inflammation, lethargy, loss of appetite, weight loss, vomiting, diarrhea, and neurologic disorders. Call your veterinarian immediately if you notice any change for the worse in your FIV positive cat.

Vaccination against FIV is no longer possible in the United States and Canada

  • FIV is transmitted through saliva; therefore, cats that are in close contact with each other (through fighting) have the highest risk of getting infected. The most at-risk cats include outdoor or stray cats, especially intact adult males, who are more likely to roam and fight for territory and food.
  • From 2002 until 2017, the FIV vaccination was available in the United States and Canada. It was generally considered safe, with rare and usually minor side effects.
  • The vaccine contained certain strains of inactivated virus, which offered protection against some (but not all) FIV infections. Research had indicated that the vaccine was only minimally effective and may actually sensitize exposed cats to infection, with vaccinates becoming infected with higher viral loads than unvaccinated cats if exposed3. In other words, vaccinated cats that were exposed to any of the strains not included in the vaccine were at full risk of getting infected. This was particularly an issue in certain geographic areas, like the United Kingdom, where the vaccine offered little-to-no protection.
  • In addition, the vaccine causes a false positive test result on the commonly used antibody-based FIV tests (ELISA and Western Blot) for up to 4 years, so determining the cat’s true FIV status may be impossible should questions arise about the cat’s health.

The Stages of FIV in Cats

There are a few different stages of FIV in cats. Here’s what to expect in each stage.

Acute Phase
The acute phase occurs after initial infection. Some cats will experience lethargy, fever, or lymph node enlargement. This stage lasts one to three months.

Latent Infection
The latent infection period has no symptoms and can last months to years. Many cats will not progress beyond this stage.

Feline Acquired Immunodeficiency Syndrome (Feline AIDS)
If a cat reaches this phase of infection, they become immunocompromised and are susceptible to secondary disease. This usually occurs years after initial infection. Feline AIDS symptoms are those that are related to secondary infections.

Terminal Phase
Once a cat reaches the terminal phase, the prognosis is approximately two to three months. During this time, it’s common to see severe infections, cancer, neurologic disease, immune-mediated disease, etc.


Cats with FIV can live very long, full lives with few complications from their disease.

  • Retrovirus-positive cats should be evaluated by a veterinarian twice a year. In addition to a thorough physical exam, a minimum database including a complete blood count, chemistry panel and urinalysis should be performed at least yearly.
  • Utilize aggressive diagnostic and treatment plans early in the course of any illness.
  • Retrovirus positive cats should be spayed or neutered, housed indoors, and should avoid raw food diets.
  • Few large controlled studies have been performed using antiviral or immunomodulating drugs for the treatment of naturally infected cats. More research is needed to identify best practices to improve long-term outcomes following retroviral infections in cats.

  1. Horizontal transmission of feline immunodeficiency virus with semen from seropositive cats; H L Jordan et al; Journal of Reproductive Immunology; December 1998;41(1-2):341-57.
  2. Transmission of feline immunodeficiency virus (FIV) among cohabiting cats in two cat rescue shelters; Annette L. Litster; The Veterinary Journal; Available online 31 March 2014 (currently in press).
  3. Limited efficacy of an inactivated feline immunodeficiency virus vaccine; S P Dunham et al; Veterinary Record; April 2006;158(16):561-2.

Information on this site is for general information purposes only and is provided without warranty or guarantee of any kind. This site is not intended to replace professional advice from your own veterinarian and nothing on this site is intended as a medical diagnosis or treatment. Any questions about your animal’s health or diet should be directed to your veterinarian.

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