Feline Immunodeficiency Virus

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What is it?

Feline Immunodeficiency Virus (FIV) is a contagious viral disease of cats. It is thought to affect around 4% of cats in the UK. It has many similarities to the human immunodeficiency virus (HIV) which causes AIDS in humans, but FIV only affects cats and is not a risk to human health. The FIV virus damages the cells in the cat's body that fight infection (the immune system). Signs of FIV infection can take a long time to develop, and FIV infected cats can live comfortably for a number of years. However, the effects of the virus on the immune system are serious, and infected cats are more likely to suffer from secondary infections.

What is the risk?

FIV is spread in the saliva and other bodily fluids of infected cats. Cats become infected by FIV usually through a bite from an infected cat. Unneutered male cats who fight over territory are more likely to be infected with FIV, and it is relatively common in the stray cat population. The virus does not frequently infect the cat's environment as it cannot survive for long outside the cat, but one bite from an infected cat can be enough to transmit infection. Indoor only cats are much less likely to become infected with FIV.

Unlike HIV, FIV sexual transmission does not seem to be an issue, but if a pregnant cat is infected with FIV, the virus may infect the kittens. Only a small minority of kittens born to FIV infected mothers will have FIV, but the mother may pass on antibodies against FIV to the kittens. For this reason, it is usually recommended to blood test kittens for the presence of FIV virus after 6 months of age. FIV is closely related to Feline Leukaemia Virus (FeLV) and while a cat with FeLV will not automatically become infected with FIV, if they do contract FIV, the disease will be more serious.

What happens to the cat?

Once infected, in the vast majority of cases, the cat cannot get rid of the virus. The first signs of infection may go unnoticed - the cat may be a little quiet and feverish for a couple of days. Over time, the virus damages the immune system by attacking cells that are involved in controlling infection. FIV infected cats are therefore more prone to developing secondary infections such as skin, urinary tract, respiratory, diarrhoea, and dental infections. This may, however, take months or years to develop.

How do you (the vet) know what is going on?

Signs of infection:
  • Generally 'under the weather'
  • Fever
  • Weight loss
  • Enlarged lymph nodes
  • Secondary infections such as chronic stomatitis (infection and inflammation in the mouth), chronic diarrhoea, skin disease, respiratory disease, may be slow to recover from these infections
  • Nervous system disorders
  • Delayed wound healing
  • Diagnosis is by blood testing for antibodies to FIV virus. No test is 100% and antibody testing occasionally may give false results. If the result is not clear, the cat's blood can be tested for the presence of the FIV virus itself, which is conclusive. Cats that are FIV positive are able to transmit the disease to other cats.


  • FIV infected cats may live comfortably for a number of years. If adopting an FIV positive cat it should be the only cat in the house and it should be indoors 100% of the time to reduce the risk of spreading infection, and of the cat picking up secondary infections.
  • If a cat with FIV is identified in a household with other cats, it is best to neuter all cats in the household, and consider removal of FIV positive cats. It is advisable to test cats for FIV that are joining a household with other cats. Ideally bringing an FIV positive cat into a household with FIV negative cats should be avoided.
  • There is no cure for FIV and affected cats are infected for life.
  • FIV positive cats should not be bred from.
  • Feed a good quality diet.
  • Secondary infections can be treated with antibiotics.
  • Short courses of steroids may help when needed.
  • There is an antiviral therapy available but it is very expensive. It can result in short term remission but side effects are common and may occasionally be severe.
  • Avoid raw feeding as affected cats may be more prone to picking up diseases from raw meat.
  • The use of human antiretroviral drugs is sometimes possible, but drugs and doses need to be very carefully monitored by your vet, as many of these medications are highly toxic to cats. They are also usually expensive.
  • Boarding facilities should be made aware that the cat is FIV positive and it should be isolated from other cats.
  • If the cat cannot live indoors for 100% of the time, or if the cat is sick with FIV and its secondary effects, then it is usually a kind decision to euthanase them.

  • How can I protect my cat from the virus?

  • There is no vaccine available for FIV in the UK.
  • Neutering reduces the risk of fighting between cats, and is therefore one of the most effective means of reducing the risk of transmission of FIV.
  • Indoor cats are highly unlikely to be exposed.