Our Guide to Feline Leukaemia Virus

What is FeLV? Feline Leukaemia Virus (FeLV) is a serious viral infection that affects cats. Around one in three cats that come into contact with the virus will develop a permanent infection. Sadly, these cats often become very unwell and may only live for a few more years.

FeLV attacks the immune system, making it harder for cats to fight off other infections. It can also damage the cells that produce red blood cells, which may lead to anaemia (low red blood cell count) and, in some cases, to certain types of cancer.

Does FeLV Cause Leukaemia in Cats?

The term leukaemia refers to an excess of abnormal white blood cells in the blood. This happens when the body starts making these cells uncontrollably, often due to genetic damage.

Sometimes, this damage prevents a gene that normally helps prevent cancer from working properly, or it causes the body to produce many abnormal, immature cells quickly.

Causes of Leukaemia in Cats

In some cats, the cause of leukaemia is unknown. In others, it may be linked to things like environmental factors, radiation, or exposure to certain chemicals.

Some cats with leukaemia, or lymphoma (a type of cancer that affects the lymph nodes and can spread to the bone marrow), will test positive for FeLV. There is a connection between FeLV and these cancers, but not all cats with the virus will develop cancer, and not all cats with cancer will have FeLV.

There are several types of leukaemia in cats. Some are more serious than others. The outlook can vary among cats with leukaemia - some cats may not be badly affected, while for others, it can sadly be life-threatening.

Infection with Feline Leukaemia Virus

FeLV cats can develop a range of health problems, including anaemia (low red blood cell count), cancers such as leukaemia and lymphoma, and a weakened immune system, which makes it harder to fight off secondary infections.

Many cats exposed to FeLV will fight off the virus and become immune, but those that don't will become persistently infected, meaning the virus stays active in their body for life.

How is FeLV Diagnosed?

FeLV infection is usually diagnosed through blood tests that look for antibodies to the virus. This may include a PCR snap test (Polymerase chain reaction), an ELISA (Enzyme-linked immunosorbent assay), or an IFA (Immunofluorescent antibody) test.

Because results can sometimes be misleading, especially early after infection, your vet will likely recommend repeating the test a few weeks later. This helps confirm whether the virus is truly present.

A positive result doesn't always mean your cat will get sick - some cats fight off the virus and become immune. On the other hand, if the test is done too soon, your cat might test negative even if they're infected, because their body hasn't had time to produce antibodies yet.

Is FeLV Contagious?

Fortunately, FeLV only affects cats - it can't be passed to dogs, humans, or other animals.

FeLV spreads through infected bodily fluid, most often saliva. Common sources of infection include mutual grooming, sharing food bowls, sneezing, or bite wounds. It can also be spread through urine, during mating, or from a mother cat to her kittens.

Who is at Risk of Infection?

Any cat that comes into contact with other cats could potentially be exposed to FeLV. The risk of infection increases the more they're exposed, but kittens under six months old are most likely to catch the virus and develop serious illness quickly.

Adult cats are more resistant to FeLV, but that doesn't mean they're completely safe. If they're around the virus often enough, they can still get sick.

FeLV is found all over the world, but how common it is depends on where you live. Outdoor cats, or cats that split their time between indoors and outside, are more likely to be exposed. Cats that are already unwell or live in homes with lots of other cats are considered high risk for FeLV exposure.

FeLV in Cats' Symptoms

FeLV symptoms vary a lot from cat to cat. It all depends on which cells are affected and how much damage the virus has done.

One of the most common problems FeLV causes is a weakened immune system. This happens when the virus destroys white blood cells, which are the body's main defence against infection. If your cat's immune system is affected, you might notice that they keep getting infections, or that infections don't respond well to treatment.

The next most common effects are anaemia and cancer. Cats with anaemia may seem really tired, low on energy, and may have pale gums.

Cancer in Cats and FeLV

When it comes to cancer, the two most common types linked to FeLV are leukaemia and lymphoma. If your cat develops one of these, they might:

• Stop eating
• Lose weight
• Cough
• Have breathing issues
• Or seem generally unwell

If your cat is showing any of these signs, it's important to speak to your vet. Catching things early can make a big difference.

What Should I Do if My Cat is Infected with FeLV?

If your cat is infected with Feline Leukaemia Virus, it's really important to prevent it from infecting other cats. FeLV-infected cats can easily transmit the virus through close contact and shared spaces.

It's best to keep your FeLV-positive cat indoors and away from other cats, including those that have received the FeLV vaccine. If you have other cats at home, permanent separation might not always be possible, so you may need to consider rehoming them to a single-cat household.

Preventing FeLV in Cats

The virus doesn't survive long outside the body, but it's still important to clean food bowls, litter boxes, and bedding regularly.

Vaccinating a cat who already has FeLV won't help, but the vaccine is a good way to protect healthy cats, especially if given before they've been exposed. It's about 80% effective at preventing infection when given early.

Because FeLV can pass from mother to kittens, infected cats should always be neutered.

Can You Treat Cats with FeLV?

If your cat becomes persistently infected, the virus remains active in the body for life and can lead to serious health problems.

However, that doesn't mean nothing can be done. Caring for a cat infected with FeLV can be challenging, but supportive treatment can still greatly improve its quality of life. With your vet's support, you can treat the virus-related conditions and help your cat stay comfortable and happy for as long as possible.

FeLV treatment focuses on managing issues like infections caused by a weakened immune system, vaccinating against other preventable diseases, and easing symptoms if your cat develops cancer, such as lymphoma.

It's important to note that not all cats exposed to FeLV will become persistently infected - some can fight off the virus and clear it from their system. But for those that don't, the long-term outlook is unfortunately poor. Around 80% of persistently infected cats have a survival time of less than three years after diagnosis.

Is There a Cure for Feline Leukaemia Virus?

Unfortunately, there's no cure for FeLV once a cat becomes persistently infected, so prevention is key. Vaccinating kittens early and testing any new cats before introducing them to your home are two of the best ways to reduce the risk.

It can be upsetting to find out your cat has FeLV, but with the right care, many cats can still enjoy a good quality of life for a while after diagnosis. If your cat becomes unwell, talk to your vet about ways to keep them comfortable.

Sadly, as the disease progresses, the kindest decision may eventually be to say goodbye, but your vet will help guide you through that when the time comes.

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Content provided from Vetstream's Vetlexicon Felis 

Vetlexicon is the world’s largest peer-reviewed online clinical reference source. All our content is written and peer-reviewed by over 1,000 of the world’s leading veterinarians, ensuring relevance, accuracy and quality.