Feline Immunodeficiency Virus (FIV) and Feline Leukemia Virus (FeLV)

FIV (feline aids) and FeLV are two different diseases of cats that affect the immune system. They are both caused by retroviruses and are spread in similar ways. Male cats are more commonly affected, with uncastrated male cats running the highest risk of contracting the diseases.

What the viruses do:

FIV and FeLV are shed via saliva.

FIV is mainly transmitted through biting. Transmission through grooming and using the same water and food bowls are possible, but is less likely. The virus can also be transmitted by a queen to her kittens via the uterus and milk.

FeLV is also transmitted through biting, but will also be transmitted easily through grooming and sharing of water and food bowls. It can also be transmitted by the queen to her kittens via the uterus, milk and grooming.

Both of these viruses infect the white blood cells. This causes the immune system to become weak and unable to fight against other viral, bacterial and fungal diseases.

Infected cats are also more prone to developing certain cancers.


Cats with FIV and FeLV can sometimes live without symptoms for years.

Cats infected with either virus sometimes have recurrent episodes of illness with periods of apparent health in between.

The symptoms seen are often from the secondary infection and can include the following:

  • Loss of appetite
  • Weight loss
  • Unkempt coat
  • Enlarged lymph nodes
  • Fever
  • Pale gums
  • Recurrent infections
  • Diarrhoea


FIV and FeLV can be diagnosed by a blood test. Both the diseases are normally tested for at the same time.


There is no cure for these viruses.

Treatment is aimed at keeping the patient free from secondary infections and treating them promptly if they do occur.

Affected cats need to be fed a good quality food. In some cases a multivitamin supplement can be used.

Immune modulator therapy can be used to try to improve the immune system in an affected cat.


We advise vaccinating all cats against FeLV as kittens at 9 weeks and 12 weeks of age. Thereafter a booster vaccination should be given every year.

Cats should also be spayed and neutered at 6 months of age to try to minimise roaming and aggressive behaviour.