Read about feline leukemia

 About Your Cat’s Feline Leukemia/Feline AIDS Test 

Feline Immunodeficiency Virus Disease In Your Cat – FIV Feline AIDS

Ron Hines DVM PhD

What Is The Difference Between feline immunodeficiency/ FIV and FeLV/ feline leukemia?

Both the Feline immunodeficiency virus (FIV) and the feline leukemia virus (FeLV) are members of the retrovirus family, a large assortment of virus that includes the human AIDS virus. The symptoms of the diseases that FIV and FeLV virus produce are very similar. Some would say identical. It is just in the frequency and speed with which they produce those illnesses that they differ. The progressive form of FeLV tends to be by far the worst of the two. Those two virus and many others in the retrovirus group have a predilection (preference) for attacking and permanently disabling cells that comprise your the immune system. (read here ) With that important defense system disabled, your cat susceptibility to infections, and tumors is greatly increased. Should your cat become infected with the FIV virus, most veterinarians believe that that virus will persist in your cat for the rest of its life. As to whether the FeLV virus persists in every cat for the remainder of its life is still debated. However how the presence of FIV affects your cat is highly variable. (ask me for Westman2019.pdf) Much of that depends on the amount of damage the virus inflicts on your cat’s CD4+ and CD8+ lymphocytes . (read here)   

Although FIV and HIV are distant relatives, humans cannot be infected by the FIV virus, cats cannot be infected by the HIV virus and dogs are not affected by either of them. A fourth retrovirus, feline foamy virus  (FFV) is also present in many cats. What health issues, if any, that FFV might cause in cats remains unknown. Some cats are positive for FIV and FFV and a few for FFV, FeLV and FIA. How these mixed viral infections might affect the health of cats is also poorly understood, but none believe that it is a positive event.

How Common Is The Feline immunodeficiency /FIV virus?

The FIV virus is quite common. In prosperous countries it is considerably more so than FeLV. The virus is present worldwide. Cornell University believes that in the United States, 2.5-5% of cats that exhibit no symptoms carry the virus. When they sampled the blood of cats that were already showing signs of various illnesses, the percentage increased to 15%. Similar increases were found for cats that were allowed to range out of doors. In another study 1.7% of cats at animal shelters and 3.1% of cats presented to animal hospitals, and 3.9% of feral and colony cats tested positive for FIV. Male cats had four times the number of positives as female cats and adult cats four time the number of positives as juvenile cats. In that sampling cats showing evidence of illness were about three times as likely to be positive for FIV than cats that did not. (ask me for AAFP Guidelines2009.pdf) In another study, 0.3% of cats tested at animal shelters and veterinary hospitals were positive for both FeLV and FIV. (read here)

At first glance, FIV+ cats appear to be more common in Australia. In house cats two years old and older that had no access to the outdoors, 13% in New South Wales, 15% in Victoria, 16% in Queensland and 20% in Western Australia were positive using the IDEXX SNAP FIV/FeLV Combo test™. (ask me for Westman2019). However some of those Australian incidence studies went door-to-door sampling cats to be sure that it wasn’t only cats that regularly visited their veterinarians who donated blood samples. ( read here )  So the American, UK and EU studies may have actually missed a lot of FIV+ cats.

Where Did My Cat Catch The Feline immunodeficiency Virus?

Cats are by nature very territorial creatures. Few are willing to allow a strange cat to invade their territory without putting up a fuss. That might be confined to some loud warnings, but it often proceeds to a brawl. Over the eons that cats and the FIV virus have evolved together, the virus has “learned” to be sure that it is found in high numbers in the saliva of FIV+ cats. (read here)

No one has studied the percentage of ruling tomcats that are FIV+. I venture that quite a few, if not all of them, are. Ohio State veterinary college estimates that an urban tomcat’s territory includes about 20 city blocks. These cats are king of their territory for a relatively short period of time. I venture that their rule ends when FIV, FeLV or repeated abscesses begin to weaken them. But by then, they have passed FIV virus on to other cat challengers.

In stable colonies of cats, the more likely mode of transfer when it occurs is likely to be allogrooming. It is also possible for a mother cat to transmit the FIV virus to its offspring. Since few kittens test positive for FIV, such transfer is likely a rare event.

What Does The FIV Virus Do To My Cat?

I mentioned at the beginning of this article that health decline associated with FIV virus is not directly due to the virus. It is due to its effect on your cat’s immune system. The generators of that system are your cat’s bone marrow and lymph nodes. With its immune defenses disabled your cat’s susceptibility to every sort of infectious disease is increased. How much more susceptible depends on the severity of the immunosupression, the length of time the virus has been present and probably also on the unique genetics of every cat.

You might wonder: “why would a virus that has persisted in cats since the species originated want to kill or weaken the very host that keeps it alive? After all, sick cats don’t move around much to spread the virus”. It has to do with survival strategy options. By having a long spreader period before symptoms begin, the FIP virus gets around that problem. During that healthy carrier period, the virus’ RNA  co-opts the cat’s own cells into make enormous numbers of virus copies – all the better to spread the disease. To do that, FIV must keep your cat’s immune system (primarily its CD4+ T cells in check [disabled]). During that early spreader period, fever is unwanted. Most virus reproduce more efficiently at normal body temperature. Other virus, such as the ones associated with feline upper respiratory tract disease follow a different strategy. They thrive in the respiratory tract where your cat’s body temperature is lower and on surfaces where your cat’s immune system has a harder time attacking them. They tend to multiply quickly, get spread through sneezes and then enter carrier states where they are never heard from again or only periodically during periods of high stress. Stress for cats often means other cats – a new opportunity to change dwellings. If virus had a brain, they would be judged to be very smart.

Another casualty of disabling the immune system is the FIV’s effect on CD8+ T cell.   Disabling them also breaks a key element in controlling the spread of cancer. Abnormal cells generate in all of us during our lifetimes. It’s the T cell’s job to find them and destroy them before they can proliferate into cancer.

FIV Symptoms

I mentioned that early cases generally show no symptoms. Some report that initially, these cats are lethargic, run fevers and have enlarged superficial lymph nodes (lymphadenopathy). However that was only documented in one early study that artificially created an artificially potent FIV variant. (read here). Most early cases go unnoticed for variable periods of time (months to years). When health issues finally do occur, unexplained low-grade fevers, weight loss, lack of normal interest, unkempt hair coat and diarrhea are the most common symptoms reported.

Eventually, secondary infections commonly occur due to immune system failure. Those cats, the term FAIDS stage (feline acquired immune deficiency syndrome stage) has been coined – in keeping with the later stages or HIV infection being termed AIDS. These cats often return blood work abnormalities such as low white and/or red blood cells counts, and low blood protein levels. Eye, respiratory tract, and mouth infections (gingivostomatitis) at advanced stages of FIV are common. Various cancers also increase in frequency. Neurological issues brought on by the virus sometimes result in seizures or behavioral changes. ( read here FIV+ cats with these issues rarely survive more than a few more months.  

Is There More Than One Type Of Feline immunodeficiency virus?

FIV isolates have been assigned five different subtypes, designated A, B, C, D and E. (read here ) In Melbourne, Australia in 2008, the Subtype A and A/B were the most common. (read here) If one of these subtypes is more pathogenic than another is unknown.

Photo from snap page here

How Will My Veterinarian Decide If My Cat Carries The Feline immunodeficiency /FIV Virus?

In the United States, the use of two brands of in-office diagnostic test are commonly used to identify cats that carry the FIV virus. Read more about those tests here .   

Cats are commonly tested when:

They are showing signs of illness that can not be readily attributed to a specific disease.

They relapse despite what should have been effective treatment.

A new cat is being considered as a new family member.

Sixty days after a pet was lost and substantial time passed before it was found or returned or after a potential FIV exposure.

 Another FIV+ cat was identified in the household.

 Prior to release for adoption from an animal shelter.

 Kittens born to FIV+ queens, initially and at 4 months of age. 

Cats that have had prior vaccinations against the FIV virus can present diagnostic challenges. Many believe that these cats are likely to return false-positive test results and require confirmational PCR tests. (read here)  Others believe that is not required. ( read here )  or ask me for Westman2019.pdf It is always wise to confirm a positive FIV test using a different brand of test or different testing method. Negative in-office (point-of-care) tests results are usually accurate. However all tests occasionally yield false-positives. When FIV test results do not agree, they are called discordant. Sixty days is a commonly chose period between repeating tests when they are discordant.

When kittens are tested, the tests need to be repeated sixty days later. That is because early false positives are possible due to persistence of the mother’s anti-FIV antibodies passed to the kitten through her first milk (colostrum). Early false negative are also possible when FIV virus numbers in the kitten are still low. Some suggest waiting up to six months before making a final decision on a kitten’s FIV status. Reference laboratory-performed tests tend to be the most reliable.

Should My Cat Be Vaccinated Against FIV?

Through 2021, I believe that Boehringer Ingelheim was still marketing Fel-O-Vax FIV in Australia composed on an inactivated feline immunodeficiency virus. This vaccine was sold in North America from 2002-2017. It is composed of a strain of inactivated (killed) FIV virus and, I believed, contained an adjuvant as well to increase its effectiveness. Although Boehringer was not specific about the reasons the vaccine was withdrawn, speculation revolves around four points: They didn’t sell enough of it to make production worthwhile. Indoor cats were thought to be at low risk of contracting FIV and the outdoor cats at higher risk rarely got vaccinations. The vaccine only offered limited protection because it only contained only one strain of FIV virus. The yearly booster shots required (or the adjuvant included in it) increased the likelihood of cats developing vaccination-related fibrosarcoma cancer. The vaccine made it possible for a cat receiving it to test positive on FIV tests for up to four years after vaccination. That was particularly unfortunate for lost cats that might be mistakenly put down at animal shelters when it was mistakenly assumed that they carried the FIV virus. Later studies in Australia found the vaccine to be only 56% protective.    

Will My Other Cats Catch The FIV Virus?

If you own both FIV-positive and FIV-negative cats and they live in peace with each other (stable, tranquil social structures), the chance that the virus will pass to the FIV-negative cats are said to be low. However I do not know of anyone who has statistically examined that. Cats differ significantly in their FIV virus loads depending on their innate ability to control virus numbers, their age and the stage of FAIDS that they are currently in. The group’s individual social habits and home environment probably also come into play. In making decision as to an individual cat’s virus load, PCR testing would probably yield the most useful information. ( read here)   

What Can I Do To Protect My Cat When It Is Still Test-Negative for FIV?

Since the vaccine against FIV is not currently available and was, at its best, only moderately effective you need to keep your cat safe from exposure to the feline immunodeficiency virus. That means no exposure to FIV+ cats or cats of unknown FIV virus status. If you are partial to having more than a single feline companion, it is possible to maintain them in isolated areas of your house. In-office tests to detect FIV-carrier cats are not foolproof. They miss some cats that are carrying the virus and falsely accuse other cats of being virus carriers. If you are going to go through the expense and inconvenience of isolating your cats to various locations in your home based on their virus status. The best way to do that is through institutionally-performed PCR tests. I referenced the abstract of an article regarding that in the previous paragraph. At last glance, the full pdf was available on ReseachGate.

The FIV virus will not survive for more than a few hours in normal household environments where common household disinfectants are used to sanitize food and water containers, litter boxes, toys and bedding. I use dilute 1:20 beach in water for utensils and mopping, 1:30 in mist bottles. Do not inhale the fumes.

What Treatment Can My Veterinarian Offer My FIV+ Cat?

No medication at your veterinarian’s disposal will cause a FIV+ cat to become an FIV- cat. Feline immunodeficiency positive cats that are in apparent good health need no special treatment. The three most common ways to confirm that are infrequent or lack of infections, close to normal laboratory blood test results and a stable body weight.


Most of the illnesses seen in FIV+ cats are due to their decreased resistance to bacterial infections. In those cats, commonly used antibiotics are quite effective. However they might need to be given for a bit longer period than non-carrier cats require.

Bacteria are clever in developing resistance to antibiotics. Some antibiotics that work in the intestine (such as metronidazole/Flagyl®) can be given indefinitely. But over time, antibiotics that perfuse the body generally loose their effectiveness against resident bacteria. So antibiotics are generally dispensed only when your cat’s condition warrants them.

Nutritional Support:

Cats with advanced FIV symptoms generally loose weight. So everything you do to encourage your cat to eat and maintain its body weight is important. I mentioned in my article on feline leukemia that a more tempting diet  prepared at home  for your cat can be very helpful in combating poor appetite and weight loss. It will also give your cat considerably more pleasure than the industrial stuff sold in cans and bags. When that is not sufficient, appetite stimulants such as mirtazapine , Entyce/Elura® or cyproheptadine might be helpful. The same goes for FIV+ cats with poor appetites.

Medications That Might Give A Boost To Your Cat’s Immune System – Immunomodulators:

Cats that face health decline as a result of the FIV virus become so because their immune systems have less ability to protect them. A number of medications have been discussed as to their ability to increase the abilities of your cat’s immune system. In my personal opinion, none of them have been satisfactorily proven to be of benefit to your FIV+ cat. But some cat owners, perhaps you, and some veterinarians believe they are worth a try on the outside chance that you might gain a little more precious time with your pet. I personally have little faith in any of them.

Lymphocyte T-Cell Immunomodulator (LTCI)

In 2006, the USDA issued a condition license for a drug called Lymphocyte T-Cell Immunomodulator (LTCI). The USDA is considerably more lax than the FDA is issuing tentative drug approvals. Since then, no articles I know of have appeared in the literature documenting the effectiveness of T Cell modulators, enhancers or adjuvants – although I see that the product is still being sold as a treatment for osteoarthritis in dogs.

Interferon Alpha

In 2017 an article appeared that claimed that interferons (IFN-α and IFN-ω) might be beneficial to FIV+ cats. They base that on a rather low quality Italian study that you can read here.   

In 2019, an article appears that claimed that oral Human Interferon Alpha was beneficial to FIV+ cats. (read here Virbac     markets an interferon product, Virbagen Omega, in the UK and EU but not as of this writing, in North America. Several of my clients have successfully obtain the drug here in the USA through a transshipped of veterinary pharmaceuticals based in the UK. They had it administered to their cats suffering from FIP . For that use, it appeared to provide no benefit to their cats.

Medicines Developed To Treat Human AIDS

A few veterinarians have attempted to treat fading FIP+ cats with drugs that are helpful to human AIDS patients. The most common of these is AZT (Retrovir®) and PMEA . The results have not been as good as one might hope for.  AZT has resulted in toxic complications in cats that include, anemia and liver or bone marrow damage.

In 2013, veterinarians at the University of California, Davis, explored the possibility that a histone inhibitor, SAHA ( vorinostat/Zolina® ) might be beneficial to FIV+ cats based on its possible ability to control HIV virus numbers. ( read here ) In 2020, the drug failed clinical trials in treatment studies of HIV patients. (read here)  

How Long Might My FLV+ Cat Live?

As many others and I mention, there is often a long asymptomatic period before your FIV+ cat show signs of illness – and a few cats never do. In a 2011 report from Germany, it was estimated that the average life expectancy forward from the time of FIV virus exposure was about 5 years. (read here )  But a 2009 study that included the same author, concluded that the median survival time of FIV-infected cats was not significantly different from non-infected cats. (read here) Estimates emanating from cat placement oriented sources and animal rights advocates tend to be considerably more optimistic than 5 years. So no one really knows.

My Last Cat Died From Feline immunodeficiency /FIV-Related Problems. When Will It Be Safe For Me To Get Another Cat Or Kitten?

I would wait a month before bringing a negative cat into an area that was home to an FIV+ or FeLV+ cat. You never know what other pathogens an immunosuppressed cat might have harbored. It is true that both viruses die very rapidly when they are outside of a cat and that the viruses are killed by ordinary household disinfectants, drying and sunshine. But for your peace of mind and out of respect to your lost family member, I think that a month or two is not too long a wait. Read my thoughts about pet loss here.   

What Special Care Does My FIV+ Cat Require?

Many feline immunodeficiency cats do not require any special care. Keep them indoors, feed them a quality or home cooked diet and enjoy each others company.

The general health of all cats suffer when they are under chronic stress. FLV+ cats are no exception. What you regard as pleasure or a minor inconvenience your cat may not. The same low-stress lifestyles I suggest for FeLV+ cats are the ones that are likely to benefit your cat: avoid stays at boarding kennels, group homes, travel, veterinary hospital inpatient care and grooming shop visits as best you can. When you travel, hire a pet sitter. Avoid any situations that appear to make you cat fearful or unhappy. All of these situations are likely to increase the stress level in their lives. Read about that here. Keep a diary of your cat’s weight. Be particularly attentive to signs of ill health or behavioral changes. Attend to your cat personally. Don’t relegate those chores to others. Regularly check your cats urinary habits and stool consistency. A once or twice a year veterinary visits for blood and urine analysis should be sufficient if there has been no noticeable change in your pet’s behavior or health. Avoid feeding them raw meat or fish. ( read here & here ) and practice scrupulous flea control.

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