Cat Olly at Lewknor adoption centre

FIV in cats

Key points for FIV cats

  • All cats – especially males – should be neutered to reduce their chances of catching FIV
  • If you have an infected FIV cat, your cat is a risk to other cats and should be kept away from them
  • Infected FIV cats can lead long and happy lives – but they should be kept indoors

FIV in cats is a condition similar to the virus that causes AIDS in people, although there is no risk of people catching AIDS from infected cats. It infects the white blood cells of the immune system, killing or damaging them. A healthy immune system is needed to fight infections and monitor for cancer in the body; so infected cats have a greater risk of disease and infection from other viruses and bacteria.

Once a cat is infected, then infection is permanent. Just as in human HIV infection, carriers of FIV may show no symptoms of the disease for years. Between two to five per cent of the UK cat population is thought to be infected, but there is a lot of regional and local variation. Un-neutered male cats are more at risk.

What are the symptoms of FIV infection?

The symptoms following infection with the virus are usually mild. The cat may have a mild fever for a few weeks and there may be enlargement of the lymph nodes (the little lumps often referred to as “glands”). But often, cats infected with FIV appear completely normal.

Months or years later, as infection progresses, the cat may develop fever, lethargy, poor appetite and weight loss. Any recurrent illnesses may suggest that the cat has FIV – or another virus, such as FeLV .

Common signs include long-lasting or recurrent diarrhoea, a runny nose and sneezing (rhinitis), inflammations of the eye and recurrent skin infections. They are also more likely to get some types of cancer.

How do FIV cats get infected?

The virus passes from cat to cat in saliva, usually through biting in fights. Un-neutered male cats are considerably more at risk of getting FIV because a single bite may be enough to infect a cat. And a cat can be infected by biting an FIV-infected cat.

About one-quarter of the kittens born to an infected mother will be infected and there is a small chance that the virus can be transmitted through sharing food bowls and by cats licking each other during grooming.

How do you know if a cat is infected?

Infected FIV cats are identified by a blood test that looks for antibodies to the disease. For reasons not yet fully understood, these antibodies cannot fight off the infection. However, the commonly used tests are not completely accurate, and cats that test positive should be confirmed using a different test from a commercial laboratory. A few FIV cats that have the virus will test negative even though they are infected.

There are several other considerations with the blood test. It cannot be used for kittens under 20 weeks born to an FIV-infected mother. Some of these kittens will have antibodies from their mother to FIV but are not infected with the virus, and these antibodies interfere with the test. If it is not known whether the mother is infected, it is best to wait until a kitten is older than 20 weeks before testing.

In addition, it can take up to 12 weeks after catching the virus before the blood test can detect that a cat has the virus. If you are worried that your cat is infected (for example, following a cat fight) you should wait for 12 weeks before testing. Finally, sick cats may not produce antibodies, so they may also test negative.

Is there a FIV cat vaccine?

There is no vaccine available currently in the UK. A vaccine is used in the United States, but it is not reliable and it does not work against all the types of FIV. It also poses problems for vets because a vaccinated cat will test positive for FIV.

My cat is infected – do I really need to keep him indoors?

FIV cats with the virus can obviously infect others, so it is responsible to keep an infected cat indoors – and it is better for the cat as well, since it reduces the chances of catching an infection. Alternatively, the cat may not have to be kept indoors; it may be possible to fence in a garden, for example, so the cat cannot get out. However, the virus is spread mainly by fighting, so it may be enough to reduce the chance of fights. Especially in areas where there are not many cats, infected females pose less of a risk, as they tend not to roam and they fight less. Neutering males reduces their urge to roam and fight. But it is obviously better for the health and welfare of cats in general if FIV-infected cats are kept out of contact with others.

How serious is it? Do FIV cats have to be put to sleep?

Recent studies have indicated that FIV may not reduce a cat’s lifespan, and cats may live for many years after being infected. However, it is unpredictable, as some cats develop severe and multiple infections. It is important to try and protect cats with FIV from catching other diseases, as they are more vulnerable than other cats. They should not be fed raw foods that might carry bacteria, such as raw eggs or meat, and it is better to keep them indoors. Hunting should be discouraged.

I have other cats in my household. What should I do?

Infected cats are a possible source of infection so other cats in the household should be FIV-tested. Ideally, all FIV-positive cats should be isolated or rehomed where there will be no contact with other cats. However, as the risk of transmission by social contact such as sharing food bowls and mutual grooming is low, many owners decide to continue keeping all their cats together. Feed cats using separate food bowls, as large amounts of the virus are present in saliva. Litter trays and food bowls should be disinfected after use to kill the virus. The virus dies outside the cat within a few hours so infection is not easily carried on objects.

Can infected FIV cats be treated?

Provided an infected cat is healthy, treatment is not necessary – there are no drugs that can “cure” a cat from the virus. Measures should be taken to protect the cat from infections. Regular vaccination to protect against illnesses such as cat flu is a good idea, although you will need to discuss with your vet whether a particular version of the vaccine is needed. Furthermore, there is some evidence that repeated vaccination can speed up the development of symptoms. If you can keep your cat isolated, it may be better not to vaccinate – again, discuss with your vet.

Good quality flea control with a product bought from the vet also reduces the chances of contracting some cat diseases. If the cat appears unwell, see a vet as soon as possible, since drug treatment for infections is likely to be necessary. Regular veterinary check-ups – say at six-monthly intervals – may be helpful. It is also a good idea to monitor your pet’s weight monthly. Weight loss can be a sign of deterioration.

In some situations, some cats that are unwell, and especially those with sore mouths (gingivitis), may benefit from the use of antiviral products that are used for human AIDS patients, such as AZT. However, this is expensive, and cats need regular blood tests for side effects. Interferons can be used, and are sometimes effective in relieving symptoms. Many other products have been suggested for use, but there is no proof that they are effective.

Treatment with drugs that affect the immune system (immunosuppressive drugs such as steroids) should be used with caution. Griseofulvin, a common treatment for ringworm, should not be given. All cats with FIV should be neutered, as this removes the stress caused by coming on heat and reduces the desire to roam and act aggressively towards other cats.

Further information – viruses and antibodies

When a virus tries to enter the body, it causes the immune system to produce various types of antibodies. These attack the invader and try to damage it so that it does not become overwhelming. It is often possible to carry out blood tests to find out if an animal has antibodies to a particular agent, and this shows whether the animal has come across that agent. It does not usually indicate whether the animal is still infected, or whether your cat has become immune.

FIV (and HIV) are different. The way they take hold in the body means the antibodies produced by infection are not strong enough to clear the virus. Detectable antibodies in the bloodstream virtually always mean that the cat is infected with FIV. However, a minority of infected cats do not produce antibodies at all.

If there is any doubt, blood tests to find the virus itself can be done, but because the amount of virus in the bloodstream is small, special tests are needed, and false positives and negatives can still occur.

From outdoor to indoor cat: making the adjustment

Securing the home

When you first confine your cat he will be alert to any opportunities to escape so take extra care to close all windows, lock cat flaps and shut doors. Also make sure that washing machine doors are kept closed and chimneys are blocked off.

It’s best to move any household plants and hidden dangers that could poison your cat should he try to chew them.

Litter trays

You will need to provide litter trays, which should be placed in a quiet, but easily accessible position away from his feeding area.

If your cat is shy or you have a busy household then a covered tray may provide your cat with more privacy. If your cat has not used a litter tray select a soft litter and leave your cat in the same room as the litter tray until he has used it.

Scratching posts

Outside your cat may have exercised his claws on trees and fencing posts. To prevent damage to your home and furnishings you will have to provide a substitute scratching post.

Making your cat feel safe

As your cat no longer has the option to move away from situations he may find stressful you will have to provide additional resting and hiding places for him. Cardboard boxes with a towel over the front or high shelves with comfortable bedding can both provide places he can go to feel safe and secure.

Providing these hiding places can be particularly important if you have more than one cat or a dog in the home. Since they can no longer choose to spend time apart their relationship may become strained and they may become less tolerant of one another.


Provide activities to prevent boredom, provide an outlet for hunting behaviour and to help keep your cat fit and reduce the risk of weight gain.

In addition to providing a range of toys you should also play interactive games with your cat. Cats enjoy games involving movement and like to be able to pounce on, grab and bite. Pulling toys along on string is a safe way of playing with your cat.  

A food ball (a specially designed ball which you fill with your cat’s dried food) is also a good way to keep your cat active. As your cat pushes the ball along pieces of his food fall out occupying his time and providing something for him to ‘hunt’. 

How to play with your cat gives you some great ways of entertaining your cat! 

— Page last updated 26/05/2023