FeLV and FIV Infections

Cats can become infected with viruses which cause immune deficiency. These viruses are the feline immunodeficiency virus (FIV) and the feline leukemia virus (FeLV). FIV and FeLV belong to the same family of viruses, called Retrovirus, as the human immunodeficiency virus (HIV), the causative agent of the human acquired immunodeficiency syndrome (AIDS). FeLV and FIV cannot infect people and cannot cause AIDS in people.

FeLV infection

That a viral infection specific to cats could cause immune dysfunction was first reported in 1965. This type of viral infection was later found to be caused by FeLV. In over 80% of FeLV exposed cats with subsequent bloodborne infection, life-threatening illness occurs. The most common illness occurring after FeLV infection is immune deficiency. FeLV can also cause life threatening illness by triggering cancer (lymphoma) or bone marrow disease (leukemia, among others).

FeLV is transmitted through intimate contact with an infected cat. The most common portal of entry for infection is the mouth and nasal cavities. If the exposure progresses to bloodborne viral infection, the infection is nearly always permanent and can be fatal.

It is estimated that after a single exposure to an infected cat, there is a 10% chance of developing FeLV infection. Fortunately, cats exposed to FeLV can sometimes fight off early infection before the virus becomes bloodborne 60% of the time. Also, fortunately, there is a vaccine available through your local veterinarian which effectively protects most cats from infection.

Once FeLV infection has occurred, there is no cure. Most of the medical care shifts at that point to reducing exposure to opportunistic infection, ensuring proper nutrition and environment conducive to maintaining feline health, and treating illness triggered by the viral infection. Treatment of the virus itself can also help infected cats remain in better health. Some of the drugs human AIDS patients receive can help feline AIDS patients.

FIV infection

The FIV agent was first isolated from infected cats in 1986. Interestingly, retrospective studies have since found that the virus has been responsible for feline AIDS at least since 1968. FIV has a worldwide distribution and it is estimated that 1-2% of cats are positive for the virus.

Older male cats (> 6 years old) with free access to the outdoors are most at risk for exposure to FIV. The primary mode of transmission is bite wounds, although prolonged close contact can also provide a risk of infection. Kittens may rarely be infected from the mother. The virus itself is easily disinfected and dies within minutes upon exposure to dry surfaces. FIV is not transmissible to people.

Infected cats may become positive on FIV blood tests within one month of exposure and may live for years without signs of illness. Once ill, signs are primarily related to the effects of opportunistic infections which gain entry into the body as its defenses fail. FIV may also directly cause blood disorders and may trigger cancer (e.g., lymphoma, leukemia, squamous cell carcinoma). There is no cure for FIV virus and a vaccine is currently not available for FIV. Initial management of FIV related AIDS is the same as for FeLV infection. Human AIDS drugs may also cause clinical improvement in FIV infected cats.

Drugs used to treat Feline AIDS

1. Reverse transcriptase inhibitors such as AZT, PMEA, or ddC can cause clinical improvement in infected cats. However, as with people, severe side effects can occur. The effectiveness and safety of protease inhibitors, another class of AIDS drugs therapy, is unknown. Before administering these potent agents to your cat, be sure your local veterinarian has experience using them in cats.

Some veterinarians will elect at that juncture to refer you to a veterinary internist at a referral center or university for continued treatment.

2. Immunotherapy can be used to treat feline AIDS. Agents including interferon alpha, staphylococcus Protein A, and Immunoregulin can cause clinical improvement in infected cats. Combination therapy using these drugs with reverse transcriptase inhibitors can also be of benefit. As always, inquire whether your veterinarian has experience administering these drugs.