The feline immunodeficiency virus (FIV), also sometimes called “feline AIDS,” is one cause of immune system disorders in domestic cats. FIV is thought to share many features with the human immunodeficiency virus (HIV), which causes AIDS in people. The feline and human viruses are species-specific, which means that HIV cannot cause infection in cats, and FIV cannot cause infection in people. Infection with FIV ultimately suppresses the cat’s immune system, allowing any number of secondary infections to flourish.
Causes & Prevention
Feline immunodeficiency virus is transmitted through the saliva and blood products of cats - most commonly through bite wounds and deep scratches. FIV disease is most common in adult, sexually intact, free-roaming males. There is no reliable evidence that the virus can be transmitted through sexual contact between cats, but infected females can pass the virus on to their kittens.
FIV infection in indoor cats is uncommon. The best way to prevent it is to keep naïve cats away from infected cats, which frequently are free-roaming neighborhood strays. For high-risk (outdoor) cats known to be FIV negative, there is a commercially available vaccine, although vaccinated cats will probably always test positive on the screening test for FIV. Reducing the stress in a cat’s environment may help ward off secondary infections associated with FIV infection. Affected cats that have not yet been neutered or spayed should be altered to reduce the stress associated with fluctuating hormone levels and to prevent the urge to mate. Neutered tom cats are less likely to fight with other cats. Cats with FIV infection should have a quiet, calm and safe indoor living environment with high-quality food, abundant fresh water and plenty of toys and activities to keep them healthy in both body and mind.
Symptoms & Signs
Cats infected with FIV can develop a number of different symptoms. Because their immune systems are weakened and unable to function normally, affected cats are predisposed to developing secondary bacterial infections that can occur almost anywhere in their bodies. Initially, most FIV-positive cats develop a mild stage of illness roughly 4 to 6 weeks after infection with the virus. However, their early symptoms may not be noticed even by attentive owners, because most cats continue to behave fairly normally. During this early stage of disease, cats may have no obvious symptoms, or they may develop one or more of the following nonspecific signs:
- Swollen lymph nodes
- Weight loss
- Lack of appetite (inappetance; anorexia)
They may also become anemic and develop superficial skin infections.
The initial phase of FIV infection is usually followed by a long latent period, during which few if any clinical signs are present. This phase can last for months or years. Most cases of FIV are diagnosed during this incubation period as part of a routine veterinary check-up or during testing for some other condition.
Eventually, FIV enters a terminal phase, during which the viral organisms replicate profusely and cause increasing – and irreversible – suppression of the cat’s immune system. When end-stage symptoms appear, they tend to be associated with secondary opportunistic bacterial infections in or around the mouth, gastrointestinal system, reproductive, urinary and respiratory tracts and eyes. Owners of cats with end-stage FIV disease may notice one or more of the following signs:
- Inflamed gums
- Oral ulcers
- Severe, chronic mouth and gum disease
- Bad breath (halitosis)
- Chronic small bowel diarrhea
- Loss of appetite (inappetance; anorexia)
- Dramatic weight loss (emaciation)
- Recurrent urinary tract infections
- Spontaneous abortions
- Recurrent upper respiratory tract infections
- Red, inflamed eyes
- Ocular opacity (cloudy eyes)
- Ocular (eye) discharge
- Retinal degeneration or hemorrhage
- Nasal discharge
- Neurologic signs (seizures; behavioral changes; dementia)
- Poor hair coat
- Chronic skin infections
- Chronic ear infections
- Hair loss (abundant)
Most veterinarians will perform a thorough physical examination and conduct routine blood work (complete blood count and serum biochemistry profile) on any cat presenting with nonspecific signs of illness. Currently, the screening test of choice for FIV infection is an enzyme-linked immunosorbent assay (ELISA test), which can detect antibodies against the virus in a cat’s saliva or serum, if it has been exposed to the virus. The ELISA test can have false-positive results, such as when the cat has been vaccinated against FIV. There presently is no test that can differentiate between antibodies produced by exposure to FIV (true infection) and antibodies produced in response to a vaccine. False-positive results can also occur in young kittens that still have circulating maternal anti-FIV antibodies derived from colostrum, and occasionally due to laboratory error. Accordingly, positive results from the ELISA screening test should be confirmed by either a Western Blot or a polymerase chain reaction (PCR) follow-up test, before a definitive diagnosis is made. The Western Blot confirmatory test is favored in cats known not to have been vaccinated against FIV, while the PCR test is preferred in cats that have been given the vaccine. Both of these tests are performed at a referral laboratory.
It can take several months for detectable levels of anti-FIV antibodies to form in the blood of infected cats. Kittens and cats with unknown vaccination histories should be tested at least twice – on two separate occasions after 6 months of age. All cats in a multi-cat household should be tested for FIV infection, and any new cats entering a multi-cat environment should be tested as well. Cats that are in a high-risk group, such as outdoor intact males or cats prone to fighting with others, should be tested for FIV at least annually. False negative ELISA results can occur very early in the course of infection, as well as in the end-stage of disease when levels of circulating anti-FIV antibodies are undetectable due to chronic immunosuppression.
There is no effective cure for feline immunodeficiency virus infection. However, there are treatment and management protocols that can help affected cats live a longer and more comfortable life. The overriding goal of treating FIV infection is to prevent or resolve the secondary opportunistic infections that can quickly become lethal due to the immunocompromised status of infected cats.
By the time FIV infection is definitively diagnosed, the veterinarian will already have performed a thorough physical examination, taken a complete history and conducted routine blood work and probably a urinalysis as well. Routine annual re-tests should be performed once a cat has been diagnosed with FIV; in some cases, these tests may be recommended more often. Infected cats’ weight should be carefully monitored. If a cat suffers dramatic sudden weight loss, the attending veterinarian may recommend nutritional and caloric supplementation.
“Treating” FIV involves treating any secondary infections, which typically requires antibiotic and/or antifungal therapy. Anti-viral drugs, such as azidothymidine (AZT), have proven helpful in some cases and may help to prolong infected cats’ quality of life. Owners can help their FIV positive cats live long, happy lives by feeding them a high-quality, highly palatable diet and keeping their living areas clean, warm and safe. Owners should also regularly examine their cats for evidence of infection, neoplasia (cancer) or progression of the primary disease. FIV-positive cats should always be kept indoors, both to reduce their exposure to infectious agents and to prevent the spread of infection to other cats. Of course, all cats should have free access to fresh water at all times.
Infection with the feline immunodeficiency virus is not necessary an accelerated death sentence for companion cats. FIV-positive pets can live for many years and may never develop observable signs of the disease. However, the virus will continue to replicate, and most FIV-positive pets will eventually develop secondary infections or cancer due to their immunocompromised state.
FIV infection is slowly progressive. Antibody-positive cats can remain happy and healthy for many years. Cats that have developed clinical signs usually will have chronic or recurrent health problems due to immunosuppression that at some point will require medical attention.