Feline Immunodeficiency Virus (FIV)

Note the statistics quoted in this page are American statistics. There are no meaningful Irish statistics on the prevalence of FIV/FeLV in Ireland, but we could assume the data would be proportionately similar.

Adapted for Ireland from Alley Cat Allies.

Feline immunodeficiency virus is a retrovirus in the lentivirus subfamily. The primary mode of transmission is through bite wounds. Because neutered cats fight much less than intact cats, transmission of FIV can be significantly reduced through neuter programs. Under natural conditions, the virus is not transmitted through nursing, mutual grooming, sharing food/water bowls, or from mother to kitten.

Feral cats and owned cats contract FIV at an equally low rate. An estimated 3-4% of all free-roaming cats1 become infected and carry the virus, but only a small portion of these cats develop symptoms related to FIV. Most FIV-infected cats live many years – sometimes their entire lives – without any visible effects from the virus.

In cats who develop FIV-related disease, the virus can cause varying degrees of immune system dysfunction. This most often manifests as a reduced ability to fight infection. For example, the classic presentation is an adult male cat with recurrent abscesses that take longer to heal than would be expected. Other types of infections caused by viruses, bacteria, and fungi may also become more serious and take longer to resolve.

Progression of the Virus

After initial infection, the virus spreads to the cat’s lymph nodes, causing them to become enlarged. Fever can develop and last for several days. Some cats experience a transiently reduced white blood cell count. During the second stage of infection, the cat is often completely asymptomatic for many years. The virus typically remains dormant for years, which may explain why many cats live a lifetime without symptoms.

If disease develops, this will occur during the third stage. In this stage the cat may develop signs of immunodeficiency and secondary conditions, such as opportunistic infections, stomatitis, ocular inflammation, cancer, and respiratory tract infections. FIV-infected cats might also develop persistent intestinal or urinary tract infections, neurological problems, kidney disease, or tumors. All of these conditions also occur in cats without FIV infection, so an association with FIV is often speculative.

A diagnosis of FIV infection is not cause for alarm. Since the virus has a long incubation period, a cat who tests FIV-positive may live free of FIV-related disease for a lifetime. Furthermore, FIV-vaccinated cats are indistinguishable from FIV-infected cats.

Against FIV Testing

CATalyst does not support testing feral cats for FIV. Besides the reasons stated previously – low rate of disease, low likelihood of transmission, long lifespan – the cost of testing is substantial. We believe that funds are more effectively invested in neutering, rather than FIV testing. In addition, as recommended by International Cat Care, if extra money is available it should go towards vaccinations.

Moreover, FIV test results can be false, inaccurate or inconclusive:

  • Standard tests only detect antibodies against the virus, not the virus itself. The presence of antibodies does not mean the cat is infected.
  • Positive FIV tests in kittens under six months of age should not be interpreted as FIV infection. Kittens are rarely infected but may test positive because antibodies can be passed from infected mothers through nursing. For more accurate interpretation, FIV-positive kittens under six months of age should be retested between eight and 12 months of age, when maternal antibodies have declined.
  • Current FIV tests cannot distinguish between cats who are infected with FIV, vaccinated against FIV, or both infected and vaccinated. The FIV vaccine stimulates the production of antibodies that are indistinguishable from those that develop from natural infection.

Care and Treatment

There is no cure for FIV, but a cat who tests FIV-positive may live free of FIV-related disease for their lifetime. By carrying out spay/neuter programs, the risk of transmission will be greatly reduced.

Read more complete information about selection and interpretation of FeLV and FIV tests and management suggestions for infected cats from the American Association of Feline Practitioners.


1 “Prevalence of feline leukemia virus infection and serum antibodies against feline immunodeficiency virus in unowned free-roaming cat,” JAVMA, Vol 220, No. 5, March 1, 2002