Can FIV+ Cats Live With Other Cats? Our Vet Explains the Science

Feline immunodeficiency virus (FIV) is an infectious disease in cats, similar to HIV (human immunodeficiency virus) in people. FIV is a complex disease that attacks the immune system and weakens it, and there is unfortunately no cure.

A big worry for owners of cats that are FIV-positive is whether they can safely live with other FIV-negative cats in a multi-cat household. Put simply, a cat with FIV can spread the disease to other cats, usually through fighting, and vets have historically advised against keeping FIV-positive cats alongside FIV-negative cats. However, a 2014 study of Transmission Of Feline Immunodeficiency Virus (FIV) Among Cohabiting Cats In Two Cat Rescue Shelters changed the way we thought about the safety of infected cats living with non-infected cats. 

The study evaluated a population of cats, in which approximately 5% were FIV-positive, over a period of 4 years. At the end of that period, no FIV-negative cats had become infected, showing a lack of virus transmission despite years of exposure to FIV-positive cats.

This does not mean that keeping infected and non-infected cats is without risk, but it does suggest that the risk of transmission, particularly amongst cats cohabiting peacefully, is actually quite low.

Let’s take a look at the facts surrounding FIV transmission and explore the risks of co-housing FIV-positive cats with FIV-negative ones.

What Is Feline Immunodeficiency Virus?

FIV is a slowly progressive virus that damages cells in the cat's immune system. The ongoing destruction of cells that are integral to the body's defense mechanisms leads to a weakened immune system, making cats vulnerable to secondary infections. In most cases, it is these secondary infections that ultimately shorten these cats' lives, rather than FIV itself. One of the challenging parts about the diagnosis of cats with FIV is that they can be positive but have no clinical signs during the asymptomatic or latent stage of illness. Cats can harbor the infection for years, and clinical signs may not be apparent for a long time.

FIV weakens the immune system of cats to the extent that they can become very unwell from illnesses that a healthy cat would be able to survive. There is no cure for the virus, only management strategies.

Clinical signs can be very subtle or generalized and non-specific. Typical signs to look for include:

• Weight loss
• Lethargy
• Fever
• Reduced appetite
• Secondary lesions in mouth and on gums
• Poor coat condition
• Swollen lymph nodes
• Discharge from eyes and nose due to secondary respiratory infections

The cat may also be generally run down and take longer than usual to recover from infections. If you see any of the above clinical signs, it is important to make an appointment with your vet so that they can be examined.

How Is Feline Immunodeficiency Virus Transmitted in Cats?

Cats that are infected with FIV typically shed the virus in their saliva, and infection is passed on through deep bites. Cats can also become infected through transmission of other bodily fluids, such as blood, and less commonly, FIV can also be transmitted sexually.

Kittens can become infected in utero, less often during birth, or just after birth. It is believed that the virus can pass across the placenta and through the mother's milk to the kittens. Interestingly, transmission of the virus from the queen to the kittens occurs in only a small percentage of cases.

The good news is that FIV is a fragile virus, unable to survive long periods outside the body. This means that it is less common for cats to pick it up in their environment. Many, if not most, cats with FIV have a history of fighting other neighborhood cats, which is how they contracted the virus. Cats that present with cat bite abscesses should be tested for FIV 8 weeks after they have been bitten to screen for the disease.

How Is Feline Immunodeficiency Virus Diagnosed in Cats?

FIV can be complicated to detect. It is diagnosed using a blood test that identifies the presence of specific antibodies to the virus. A test called an ELISA is commonly used. If the test comes back positive, this means that the cat has been exposed to the virus and has produced antibodies. It can also mean that the cat is currently infected by the virus, but the test may produce false positives. These can occur if a cat has received a vaccination against FIV. The test is not able to tell the difference between antibodies produced by an infection with the disease and antibodies induced by a vaccine.

If a cat has been recently infected, they may produce a false negative test as antibodies to the virus can take anywhere from 8 weeks to 6 months to develop. False positive tests may also be seen in young kittens who have received antibodies from their mother across the placenta or via the milk when nursing. Because of this, any kittens that are 4 months old or younger and have tested positive, need to be retested when they are over 6 months old.

Due to these issues with testing, it is recommended that any cats testing positive should be retested at a later date. The blood test should be sent off for a PCR test or a Western blot test as these are more definitive and can give more comprehensive results.

What Does the Research Say?

Recent studies have suggested that there is a low risk of transmission through casual contact in multicat households. There have also been suggestions that the presence of Feline Leukemia Virus (FeLV) could increase the risk of FIV transmission.¹ This is why it is so important to test cats for viruses such as FeLV before introducing them to FIV-positive cats.

Cats that are kept indoors and therefore do not encounter other cats not in their household have a lower risk of potential transmission.

Vaccines and FIV

There are vaccines available for FIV, but their effectiveness has been highly inconsistent, likely due to geographical variations in the virus. A vaccine has not been available in the United States since 2016, and is currently available mainly in Australia, New Zealand, and Japan. Vaccines are also problematic when it comes to interpreting the results, because a cat that has been vaccinated will test positive for FIV. There is no way to determine if the antibodies have been made in response to an infection or if they have been induced by a vaccine.

There is no known benefit to giving the vaccine to a cat that is already infected with FIV. Therefore, it is necessary to test cats and kittens whose clinical history is unknown before they receive a vaccination.

Can FIV-Positive Cats Live with FIV-Negative Cats?

The risk of an FIV-positive cat spreading the disease to FIV-negative cats is relatively low, particularly in a harmonious household. However, the risk is not zero, and separating infected cats from non-infected cats is the only way to prevent transmission of the virus. 

This does not mean an FIV-positive cat cannot live with FIV-negative cats, but the health of the non-infected cats and household dynamics need to be considered. Cats infected with FeLV should not be allowed to mix with FIV-positive cats, as there is a much higher risk of transmission in these cases.

How to Care for a Cat with FIV

Cats with FIV can still live a long and healthy life despite having the disease. There are a few changes that need to be made, which include:

• Housing them on their own or with other FIV-positive cats if possible: Although research does indicate that the risk of transmission between cats living together is actually quite low, the risk still exists, and separation is the only way to be certain that the virus won’t spread. However, it should not be assumed that an FIV-positive cat poses a high risk to other cats, and precautions can minimize those risks significantly.

• Neutering/Spaying cats: Most cats are infected with FIV through fighting, and the most aggressive and contentious fights tend to happen between males competing for mates. Neutering and spaying your cat by the time they are 6 months old is one of the most important things you can do for their health.  

• Keep them indoors: If you have a cat that has tested positive for FIV, it is important to keep them indoors. Not only does this protect them from picking up other illnesses, but it also protects other cats in the area. As FIV is typically spread through fighting, an infected cat is more likely to transmit the virus to cats it meets outdoors than those with whom it shares its home. Instead, install a catio or train them to walk on a leash to allow them to enjoy the outdoors safely. 

• Ensuring they are in good health: It is very important that FIV-positive cats are kept as healthy as possible. Their compromised immune system means that even minor infections or injuries can become life-threatening, so a “wait and see” approach is not appropriate for cats with FIV. They should be taken to the vet as soon as they show any clinical signs of being ill. They should be vaccinated regularly, kept up to date with flea and worm treatment, and have regular dental check-ups.

Conclusion

In the past, veterinary advice has always been to keep FIV-negative cats separated from those infected with FIV. However, research has shown that cats living together appear to have a low risk of disease transmission, and it is possible for FIV-positive cats to live alongside FIV-negative cats, provided precautions are taken and risks are understood.

Because Feline Leukemia Virus (FeLV) increases susceptibility to FIV, all cats should be FeLV tested before introducing an FIV-positive cat.

FIV is most commonly spread through deep bites when cats are fighting. Minor squabbles and occasional friction between cats living together are unlikely to lead to transmission of the virus, but if cats are regularly fighting, the risk becomes too great. It’s important to recognize that introducing a cat with FIV to non-infected cats does pose a risk, and even in the most harmonious of clowders, it is impossible to guarantee that a moment of aggression won’t occur.

Although cats with FIV can live long, happy, and relatively healthy lives, it can be a debilitating disease, and its spread needs to be prevented. The most important ways to prevent its spread are spaying/neutering cats and preventing infected cats from roaming the neighborhood. Keeping cats indoors is the best way to stop the spread of the virus and protect uninfected cats.

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