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Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) are two of the most prevalent infectious diseases affecting cats throughout the world. Both of these viruses weaken the immune system, which can leave infected cats vulnerable to other illnesses and diseases. Neither FIV nor FeLV has a cure, meaning that once a cat is infected by either of them, the diagnosis could be lifelong.
While the idea of having a pet with an incurable disease may seem scary, cats with FIV or FeLV can still lead very fulfilling — and in some cases, completely normal — lives. We spoke with Dr. Fiona Land, a clinic veterinarian at the MSPCA-Angell at Northeast Animal Shelter in Salem, to learn more about FIV and FeLV. She shared her insight into both of these viruses, including how they’re passed between cats, how they impact a cat’s overall health and lifespan, and what people should know if they are adopting a cat with FIV or FeLV.
Dr. Land: FeLV and FIV are two of the most important viruses for cats worldwide.
They’re both something called retroviruses, which means that they incorporate themselves into a cat’s DNA and can then cause lifelong health issues.
The other big similarity between these two viruses is that there’s no specific treatment or cure for either of them.
Dr. Land: FIV is mainly transmitted through bite wounds. There can be transmission from mom to babies, if the mom is infected. Otherwise, it tends to be prevalent in adult intact male cats who have been fighting with each other, while outdoor or stray cats who are unneutered have the highest risk of contracting FIV. It really can’t be transmitted through casual contact or interactions with FIV-positive cats, so touching them or sharing space with them doesn’t pose a risk.
FIV is similar to HIV in humans in that it’s a lifelong virus that eventually leads to immune suppression and AIDS-like symptoms. FIV-positive cats do typically have a nearly normal lifespan when they’re in a good home and well taken care of.
FeLV is transmitted mainly through saliva. It can be transmitted from a mother cat who is infected with the virus to her kittens. It can also be transmitted through urine, feces, and blood. It’s typically transmitted when there is prolonged contact with an FeLV-positive cat, such as in a shared home where cats are eating out of the same food bowls or are grooming each other. It’s not really something that you can spread by just petting a FeLV-positive cat and then passing it on to another cat.
Once a cat is exposed to FeLV, what happens next really depends on their immune response to the virus, leading to an abortive, progressive, or regressive infection. The prognosis for a cat exposed to FeLV varies greatly depending on which of these three infection types it has.
If a cat has a good, fast immune response, they can be exposed to the virus, clear the virus from their system, and then be absolutely fine. When that happens, we call it an abortive infection, meaning that the cat manages to fight off the virus and eliminate it from their system before it can incorporate itself into their DNA and have lasting effects on their health.
However, if a cat has no significant immune response after being exposed to FeLV, then they tend to get a progressive infection. This means that the virus is active in their body, and it’s replicating in their bone marrow, making them contagious to other cats and likely to develop other health issues because of the virus.
A cat can also have something called a regressive infection, which is where their immune system has some degree of response. In these cases, the immune system stops the virus from continuing to replicate and shed, so they can’t infect other cats and aren’t likely to experience any health issues because of the virus. Typically, those cats have a good prognosis. However, because their immune systems don’t fully eliminate the virus, the virus does still incorporate itself into their DNA, and there is a chance that the virus can reactivate and cause disease later in life.
Although regressive cats are theoretically not contagious, we still recommend that they live indoors and in homes where they’re either the only cat or all of the other cats are also FeLV-positive. We can’t predict whether an immune system shift will happen in regressive cats, and in some cases, it’s possible that they could become progressive and start shedding the virus, which would make them contagious.
Dr. Land: The vast majority of these cats have no symptoms at all. Usually, we diagnose them based on screening tests. For example, at the shelter, we screen all of our cat intakes for FeLV and run targeted screening for FIV, which means we test high-risk cats like intact males or cats with wounds.
Whenever you bring a new cat into your household, primary care veterinarians recommend a screening, so you can know whether you’re bringing these viruses into your home and exposing any other cats to them. If your cat is sick with some other disease, illness, or infection, we also generally recommend a screening as part of any blood work or diagnostic workup.
Most of the time, FeLV- and FIV-positive cats are completely asymptomatic and can live for years without showing any signs. However, depending on the progression of an infection, these viruses can cause other health issues that present symptoms.
For example, with FeLV, a cat can develop certain types of cancer, such as lymphoma, and will have symptoms like trouble breathing and anemia. They can also develop secondary infections because their immune systems are compromised by the virus and are not working well, so they may come in with bad respiratory infections. These cats may be living really happy, completely healthy lives for years, and then they just suddenly decline and show serious signs of sickness, including weight loss, tumors, weakness, and lethargy.
For FIV-positive cats, if they experience a decline, it tends to show up with immune system issues. You can see things like dental disease — such as inflammation in their mouths or gingivitis — or more common infections, like upper respiratory infections or skin infections.
Dr. Land: For FeLV, cats with progressive disease have a median lifespan of about two or three years from diagnosis, if they’re healthy at the point of diagnosis. For cats with regressive disease, a lot of them are living completely normal lives that are comparable to those of healthy cats. They could live as long as any other cat would live, as long as their FeLV infections don’t progress.
With FIV, most cats make it until they’re seniors. Their lifespans are really similar to those of other cats — just with an extra layer of increased risk due to the immune system effects of FIV.
Dr. Land: Probably the most important thing you can do is to keep your cat indoors. Indoor-only cats have virtually zero risk of getting FeLV and FIV because they’re not being exposed to other cats who may be shedding these viruses. I would recommend taking precautions to ensure your cat is unable to escape the house, and I would also definitely recommend having your cat spayed or neutered to prevent viral transmission through breeding.
If you do have a cat who goes outdoors, I would definitely talk to your vet about the FeLV vaccination. It’s extremely effective and is recommended for cats who have the potential to be exposed to FeLV-positive cats. At this point in time, though, there’s no vaccine for FIV that is available or recommended.
Dr. Land: Take really good general care of them! Make sure that they’re eating good-quality, complete food, and that they receive regular preventive veterinary care. They should have annual or twice-annual checkups with a veterinarian who knows their status to keep an eye on their health and ensure they’re receiving any additional support they might need.
If they do show any signs of illness, I would be proactive about seeking veterinary care. Even if it doesn’t seem like a big deal, they may need additional support or treatment because of their compromised immune systems. For example, they may need antibiotics for a milder infection that another animal might be able to get over on their own.
Dr. Land: I would say that we almost always have FeLV-positive or FIV-positive cats up for adoption in our MSPCA-Angell shelters! Oftentimes, at the point that we diagnose them, they’re otherwise completely clinically healthy, but they do stay longer in the shelter than other cats because not everybody wants to adopt a cat with either of those diagnoses. However, the feedback that we receive from adopters about these cats is almost always positive. They tell us that these cats have a great quality of life — for however long their lives are — and are very happy.
For that reason, I encourage people to treat these cats as if they were any other animal and give them a chance at having a wonderful home. For some of them, their lifespans are going to be just as long as any other cat, particularly those with FIV or regressive FeLV. The cats with progressive FeLV might not live as long, but adopters absolutely love having them in their homes, are happy with the impact they’ve had on their lives, and would recommend them to others.
