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FIV – Feline Immunodeficiency Virus

FIV stands for “feline immunodeficiency virus,” just as HIV stands for human immunodeficiency virus. In fact, these two viruses are closely related and much of the general information that has become common knowledge for HIV also holds true for FIV. FIV is a virus that causes AIDS in cats; however, there is a long asymptomatic period before AIDS occurs and our job is to prolong this asymptomatic period. The average life expectancy from the time of diagnosis for FIV is 5 years. Humans cannot be infected with FIV; FIV is a cats-only infection.

How Is FIV Diagnosed?

Most of the time, infection from FIV is discovered using a screening test performed in your veterinarian’s office or from a blood panel run at your veterinarian’s reference laboratory. Once a cat has been identified as positive by a screening test, a follow-up confirmation test called a “Western Blot” is the next step. Once this test is positive, the cat is considered to be truly infected.

It should be noted that administration of the new vaccine recently released for commercial use will cause a cat to test positive on both of the above tests. We do not currently have a test that will distinguish a vaccinated cat from a truly positive cat.

My hospital is not currently recommending this vaccine for now.

If you are like most of the cat-owning community, you may have a vague familiarity with the FIV virus but are unclear on the details. You may not even be sure about the difference between the FIV virus and the FeLV virus, and you rely on your veterinarian to tell you what you need to know.

Fortunately, for most cat owners the FIV virus has been an academic matter. A new kitten receives a screening test around age 6 months. Cats are often re-tested when they are ill, but since most of our feline patients live their entire lives indoors, the FIV virus is not of much concern.

For outdoor cats, it is a whole other story. The FIV virus is spread by bite wounds between cats. Adult cats, rather than kittens, are at risk. The American Association of Feline Practitioners recommends that outdoor cats be tested annually for this virus and for the Feline Leukemia Virus (the “FeLV” virus).

FIV, like HIV, can live in its host’s body for years before leading to a life-threatening AIDS situation. Ultimately, FIV is suppressive to the immune system and the average life expectancy from the time of diagnosis is 5 years.

In August 2002, Fort Dodge Animal Health released a vaccine for FIV and promoted it heavily. My hospital has looked long and hard at this vaccine which, on the surface, seems like a good idea for outdoor cats or cats living with FIV-positive housemate cats. I choose to say no to this vaccine at least until more information is available. I’m happy to list the features of the product that leave us with reservations.

There are five strains of FIV virus, called “Clades.” The vaccine was made using Clades A and D and tested using Clade A. Clade B, for example, is a very common strain in most regions of the United States and no testing of the vaccine has been performed thus far against Clade B. This means that a pet owner might wrongly believe they were protecting their cat fully against the FIV virus with this vaccine. California has both Clades A and B.
The FIV vaccine is “adjuvanted.” An adjuvant is an additive used with killed vaccines to improve their ability to stimulate the immune system. Unfortunately, adjuvanted vaccines have been implicated in the development of certain tumors in the cat. My hospital currently does not use adjuvanted vaccines for cats, and has no desire to administer a vaccine that stimulates tumor growth even under rare circumstances.
Vaccinated cats will test positive on all current methods of testing for the FIV virus. This means it will no longer be possible to distinguish vaccinated cats from truly infected cats. The vaccine is advertised at protecting 82% of cats, which means 18% can still be infected. This is nearly a one in five chance of unknowingly having an infected cat.

FIV infection is preventable by keeping cats indoors and preventing cat fights.

We choose to wait this out a bit and see how the FIV vaccination is faring a year or so hence.

How Did My Cat Get Infected?

The major route of virus transmission is by the deep bite wounds that occur during fighting. There are other means of spreading the virus but they are less common. Mother cats cannot readily infect their kittens (except in the initial stages of infection). FIV can be transmitted sexually and via improperly screened blood transfusions. Casual contact such as sharing food bowls or snuggling is very unlikely to be associated with transmission.

Isolation of an FIV+ cat is not necessary in a stable household unless the FIV+ cat is likely to fight with the other residents.

What Do I Do Now?

Some lifestyle changes will probably be needed now that you know you have an FIV+ cat.

Keep Your Cat Indoors Only

Now that you know your cat has an infectious disease, the responsible thing is to prevent the spread of this disease in your community. This means that your cat will need to begin life as an indoor cat. Cats who are used to living outdoors will make a fuss about being allowed outside. It is crucial that you do not give in as this
will simply reinforce the crying and fussing. If you just allow the fussing to run its course, it will cease and the cat will get used to its new indoor only life.

Cats who are inclined to slip past people entering the home when the door is open can be managed by leaving them in a closed room when someone is out of the house. This way, when the person arrives home, the cat does not have access to the front door.

No Raw Foods

There are currently numerous fad diets involving raw foods for pets. It is crucial that one not succumb to these popular recommendations when it comes to the FIV+ cat. Uncooked foods, meats especially, can include parasites and pathogens that a cat with a normal immune system might be able to handle but an FIV+ cat might not. Stick to the major reputable cat food brands.


Vaccination should be continued for these cats just as they are for other cats. Some experts recommend using only killed vaccines to avoid any possible reversion to virulence of the live vaccine virus strains. This has not panned out as a problem in reality, plus the killed vaccines have been associated with vaccine-associated fibrosarcomas, an additional problem an FIV+ cat does not need. We still recommend live virus vaccines for FIV+ cats just as we do for FIV- cats.

Parasite Control

The last thing an FIV+ cat needs is fleas, worms, or mites, especially now that he is going to be an indoor cat. There are numerous effective products on the market for parasite control. Consult with your veterinarian about which parasites you should be especially concerned with and which product is right for you.

Immune-Stimulating Agents

There are numerous products on the market claiming to stimulate the immune system of the FIV+ cat. These include Acemannan, levamisole, Immunoregulin®, and Interferon Alpha. None of these products have been shown definitively to be helpful though it appears that they certainly do not do any harm. Our hospital recommends Interferon Alpha for asymptomatic cats as it is relatively inexpensive and our impression is that it helps. Interferon alpha is used in an extremely dilute form (not the much higher anti-viral doses) and is used as a salty liquid added to the cat’s food or administered orally on a daily basis.

General Monitoring

While a non-geriatric FIV- cat should have an annual examination, the FIV+ cat should have a check-up twice a year. Annually, a full blood panel and urinalysis is prudent. Also, it is important to be vigilant of any changes in the FIV+ cat. Small changes that one might not think would be significant in an FIV- cat, should probably be thoroughly explored in an FIV+ cat.

What About Medications Used in HIV+ Humans?

AZT (brand name Retrovir®) is a prominent antiviral medication for the treatment of human HIV infection. Tests in FIV+ cats indicate that those with either neurologic signs or with stomatitis (oral inflammation) may benefit most. At this time at least (in cats), AZT seems to be something to save for when symptoms of viral infection appear. There are some bone marrow issues with red blood production and some periodic monitoring tests are advisable. If problems arise, fortunately, they are reversible and should resolve with a few days of discontinuing medication.

Drugs other than AZT seem to have more potential for toxicity and are not recommended for feline use.

The Immune-Suppressed Owner

Immune-suppressed cats and immune-suppressed owners do not mix well. Those who are immune suppressed, be they human or non-human, are inclined to become infected with opportunistic organisms, and in turn shed larger numbers of those organisms than one might naturally come into contact with in the environment. This means that someone who is immune-suppressed (human or not) can serve as an amplifier for infectious agents. An immune-suppressed cat can increase an immune-suppressed human’s exposure to infectious agents and vice versa. This is obviously not a good situation. The same is true for multiple immune-suppressed cats living together. If possible, there should be only one immune-suppressed individual per home.


By Wendy C. Brooks, DVM, DipABVP

One thought on “FIV – Feline Immunodeficiency Virus

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