Feline Immunodeficiency Virus (FIV) was first identified as an infectious agent of cats in 1986. This virus is related to Feline Leukemia Virus (FeLV). Both viruses affect cats in similar ways, primarily by interfering with the immune system's ability to ward off infections. FIV is similar in many ways to the human AIDS virus also known as the Human Immunodeficiency Virus or HIV. However, FIV does not affect humans, and HIV does not affect cats.
Bite wounds are the main means of transmission from one cat to another. The aggressive behavior exhibited by many free-roaming male cats puts them at a much greater risk of infection. Therefore, exposure to feral cats is the biggest threat to your cat. Casual (non-aggressive) contact within cat populations does not appear to cause the spread of FIV. Sexual transmission is not thought to be a primary means of spreading infection. However, aggressive males may bite the back or neck of the female during mating which can lead to virus transmission. In such cases, it is the bite, not copulation that leads to infection. Although uncommon, FIV can also be transmitted from the queen to her offspring. This is most likely to occur if the queen is infected during pregnancy. When a female is heavily infected during pregnancy, it has been reported that there is a chance for passage of the virus to the unborn fetus in the uterus, during passage of the fetus through the birth canal, or subsequently to newborns through the milk. It is notable that FIV is not as contagious as FeLV, in which social contact such as eating and drinking from the same bowl and intercat grooming may be a source of transmission.
Depending on the environmental stress and potential pathogens to which the cat may be exposed, FIV-infected cats may appear normal for many years following infection. However, at some later time the virus becomes active. When it becomes active, it suppresses the ability of the cat's immune system to fight disease. Cats that become ill from its effects usually have a mild disease that becomes life threatening because the body's immune system is not able to respond properly. Most cats eventually die from a secondary infection.
Since FIV infection causes an immune deficiency state, there are no classic signs associated with the disease itself. Infected cats will often have persistent fevers and appear to be in generally poor condition. Poor body condition and hair coat may be the only initial complaint. Nearly 50% of the infected cats will at some point show signs of inflamed gums and mouth. Chronic eye, urinary, skin, and upper respiratory infections are often seen as the disease progresses. Persistent diarrhea and weight loss may be the first clinical signs. In females, breeding disorders or abortion may occur. As the disease progresses, neurological disorders including seizures may develop. Most confusing to both the owner and veterinarian is the recovery to near normal between episodes, often leading to the incorrect assumption that the various clinical signs are not related.
All cats should be tested for FIV under the following circumstances: when cats or kittens (regardless of age) are newly adopted (even if they will be the only cat in the household), when cats live in households with unknown FIV status, when cats have had a potential exposure (such as bite wounds), annually when cats are at high risk of infection (those that fight or those that live with FIV-infected cats, or whenever cats are ill (regardless of previous negative FIV results). Cats that have been bitten by another cat of unknown FIV status should be tested a minimum of 60 days post-exposure. Occasionally kittens less than 6 months of age will test positive due to the presence of maternal antibodies in their blood, but they may not be infected with FIV. These kittens should be retested at 60-day intervals until they either test negative or their true FIV status is determined after 6 months of age by a more specific assay.
An FIV vaccine is now available for kittens as young as 8 weeks of age. Three injections are required at 2-4-week intervals during the first year a cat is vaccinated. A single booster is needed annually thereafter. No vaccine protects 100% of its recipients against disease. The estimated effectiveness of this vaccine is about 85%. There is also a potential problem with testing a cat for FIV if that cat has been vaccinated with the FIV vaccine, since the routine test for FIV in cats determines the presence of antibodies (or the cat’s response to the virus). Following vaccination with the FIV vaccine, the cat will develop an antibody titer. This antibody titer is the same as the antibody titer that will occur if an active FIV infection is present. Therefore, confusion can arise. Testing a cat that is infected with FIV will produce a positive test result. Testing a cat that was vaccinated with the FIV vaccine will also produce a positive test result. Therefore, to avoid this confusion, most veterinarians require that cats be tested for FIV BEFORE they are vaccinated. A test performed within 3 months of the first vaccine is considered current. In addition, any cat vaccinated with the FIV vaccine should be implanted with a microchip for identification, in case they should get lost Without identification, an FIV-vaccinated cat could be confused with an FIV-infected cat and potentially euthanized. In fact, any cat that roams outdoors should have a microchip implanted.
If you have any questions regarding FIV testing or whether it is advisable to vaccinate your cat for FIV, please contact your veterinarian.