Feline Leukaemia Virus in Cats: Symptoms, Testing and Prevention (Sydney Vet Guide)

Posted on 10 June 2026

Feline leukaemia virus is one of the leading causes of death in cats worldwide. Most owners have never heard of it.

Feline leukaemia virus is a serious infection that weakens the immune system and can lead to cancer and other life-threatening conditions. Outdoor cats are particularly at risk. Here is what you need to know.

What is feline leukaemia virus?

Feline leukaemia virus interferes with a cat's immune system, making it much harder for them to fight off infections and disease. Over time it can lead to conditions including lymphoma, severe anaemia, and persistent infections. It does not spread to humans.

How does it spread?

It spreads mainly through close, prolonged contact between cats including mutual grooming, sharing food and water bowls, sharing a litter tray, bite wounds, and from an infected mother to her kittens. The virus does not survive long outside the cat's body, so brief or casual contact is unlikely to spread it. Outdoor cats that mix with other cats are at the highest risk.

What are the symptoms?

Many infected cats appear completely normal for months or even years. When symptoms do appear they may include weight loss, lethargy, loss of appetite, pale gums, swollen lymph nodes, and recurring illness that does not respond to treatment. Regular testing is the best way to catch it early.

If your cat is not recovering as expected from another illness, give us a call as feline leukaemia virus is sometimes discovered this way.

Call us on 02 9631 9322

Can it be treated?

There is no cure. Treatment focuses on managing secondary conditions and keeping your cat as comfortable as possible. Some cats with a milder form of infection live normal lives. The earlier it is detected, the better we can manage it.

Testing

A simple in-clinic blood test checks for feline leukaemia virus. We recommend testing any new cat before introducing them to other cats at home, and regularly for cats that spend time outdoors. It is also important to know your cat's status before vaccination, as the vaccine is only beneficial for cats that are not already infected.

How do you prevent it? Vaccination!

At Great Western Animal Hospital we recommend:

F3 for all cats, which covers Feline Parvovirus, Herpesvirus, and Calicivirus
F5 for outdoor cats that are FIV positive, which adds Chlamydophila and Feline Leukaemia protection
F6 for outdoor cats that are FIV negative, which covers everything in the F5 plus the FIV vaccine

Feline leukaemia vaccination is included in both the F5 and F6 for any cat that spends time outdoors.

Kitten vaccination schedule:

First vaccine: 6 to 8 weeks
Second vaccine: 10 to 12 weeks
Third vaccine: 16 weeks or older
First booster: 12 months after the final kitten vaccine

Call us on 02 9631 9322

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Common questions

"My cat lives indoors. Do they need this vaccine?"
Indoor only cats are at very low risk. Our team will assess your cat's lifestyle and advise whether it is recommended.

"If my cat tests positive does that mean they will get cancer?"
Not necessarily. Some cats live normal lives with no serious illness. Regular monitoring gives us the best chance of catching any problems early.