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FIV (Feline Immunodeficiency Virus) is a retrovirus similar to FeLV (Feline Leukemia Virus) and the human AIDS virus. It was first discovered and isolated in 1986. It is estimated that 1 in 12 cats are infected with FIV. Some specialists believe that FIV is currently under-diagnosed. Although FIV is predominantly found in male cats, females can and do get this disease.

Here are four stages of FIV infection

Stage 1: The acute stage of infection. This stage seems most prominent in kittens and geriatric cats. In this stage the owner may or may not notice enlarged lymph nodes (lymphadenopathy) and fever. Blood work reveals decreased neutrophils (white blood cells). The acute stage may last for days, weeks or months.

Stage 2: The asymptomatic stage. There are no obvious clinical signs or laboratory evidence of infection other than the presence of FIV antibodies. Most cats are identified as positive in this stage of infection by routine testing. Persistently affected cats may appear normal for years.

Stage 3: Characterized by nonspecific clinical signs. There may be lymphadenopathy, fever, apathy, decreased white blood cells (leukopenia) and inflammatory eye diseases. Stomatitis (inflammation of the mouth and gums) or behavioral changes may develop in this stage. In this stage, the cat’s ability to protect itself against infection is compromised. The same bacteria, viruses, protozoa and fungi that are found in cats’ everyday environment—where they usually do not affect healthy animals—can cause severe illness in cats with weakened immune systems. These secondary infections are responsible for most of the clinical signs associated with FIV infection, and are the major cause of death in FIV positive cats.

Stage 4: The terminal AIDS-like stage. This stage is characterized by the classic AIDS-related complex—wasting, immunodeficiency problems with many secondary infections, neoplasia (cancer) and neurologic problems. This stage usually lasts only a few months.


Transmission can be vertical (passed on from the mother cat to the kittens) or horizontal (bite wounds are the primary mode of transmission.) Acute infection of the queen is the highest risk of transmission to the kitten. Fortunately, this is a rare event. Most young kittens that initially test positive on the antibody test ultimately prove to be uninfected. A kitten with a negative FIV test is likely to be uninfected, but the absence of antibody is not always indicative of being infection free. Conversely, the presence of FIV antibody does not always indicate that the virus is present. Kittens may have detectable maternal antibodies for up to 6 months of age. When a kitten or cat tests positive, we recommend re-testing in 2-3 months to see if he has sero-converted to negative.

Testing recommendations

  1. It is recommended for all kittens 8-9 weeks of age to be tested for FeLV and FIV. If a positive FIV test is obtained, recommend isolating that kitten and re-testing at 6 months of age.
  2. It is recommended that all stray cats be tested for FeLV and FIV. Asymptomatic cats that test positive for FIV should be isolated and re-tested in 2-3 months.
  3. Any sick cat should be tested for FeLV and FIV.
  4. Specialists recommend that all adult cats at risk be periodically tested for FeLV and FIV to allow for identification of infected cats so that owners can take the appropriate steps to protect their cat and prevent the spread of infection.

Disease management

  • Provide a stress-free environment when at all possible.
  • Provide a high quality, balanced diet.
  • Be observant for secondary infections and treat them aggressively as soon as they are noticed.
  • Regular, frequent physical examinations.
  • If intact, the cat should be spayed or neutered.
  • Strongly recommend that all FIV positive cats stay indoors to avoid some of the things that can endanger their health and to ensure that they don’t endanger the health of neighborhood cats.
  • If one cat tests positive in a multi-cat household, it is recommended that all cats be tested. It is also recommended that all cats be kept indoors and no new cats are exposed or brought into the household.

Safety and efficacy of the new FIV vaccine

It took ten years for this vaccine to be researched, tested, licensed and approved. To be licensed, the FIV vaccine had to demonstrate at least a one year duration of immunity, prevention of infection for at least 1 year, and show prevention of the virus infecting the animal. This is a remarkable development in that most vaccines approved today are labeled only as an aid in the prevention of disease, not infection. There are five different strains of FIV virus. This vaccine contains two different subtypes A and D. It has proven to be efficacious against strains A, B, and D. In one challenge study performed 375 days after vaccination, 84% of the vaccinated cats in the study were protected based upon stringent testing requirements. It is not known at this point how long the immunity lasts and if vaccines can be given longer than one year apart to achieve these same levels of protection. Long term studies are planned.

In a field safety trial in which 2,000 doses of vaccine were administered, there were no local or systemic reactions in 99.12% of vaccinated cats. There is less than 1 percent chance of reaction to this vaccine. Common reactions seen were injection site pain, vomiting, diarrhea, lethargy and fever. None of the cats experiencing these symptoms required systemic treatment.

The FIV vaccine is a killed virus, therefore it is not capable of causing FIV infection. It is adjuvanted with an immune stimulator approved for subcutaneous administration. No long-term studies have been performed yet to determine risk of vaccine associated sarcoma. Fort Dodge has stated that they believe the risk should be similar to that of the Feline Leukemia Virus vaccine. Studies have shown that the risk of vaccine associated sarcoma due to FeLV or Rabies vaccine to be 4 in 10,000 cats or 0.04%. Remember the risk of infection with out vaccination is over 8%.

Because the FIV test currently available is an antibody test, any cat vaccinated with the FIV vaccine will test positive on this test. It is believed that an antigen based FIV test will become available in the near future to help determine whether a positive result is due to infection or vaccination. Because FIV vaccinated cats will show up as positive on the antibody test, it is recommended that all cats be tested for FIV prior to vaccination.

Who should be given the FIV vaccine and when

  1. Any cat that spends even a small amount of time outdoors.
  2. Any cat that is exposed to other cats who spend time outdoors.
  3. If there is any chance of the cat escaping outdoors.
  4. If your cat (or cats) is completely indoors and not exposed to any other cats, then your cat does not need either the FeLV or the FIV vaccine.

For the initial series of vaccinations, cats need 3 injections, 3 weeks apart. After the series of 3 vaccinations is completed, the cat will receive annual booster vaccinations.

IT IS RECOMMENDED THAT ALL CATS BE TESTED FOR FIV PRIOR TO VACCINATION. If a young kitten (less than 6 months) tests positive for FIV, it is recommended to wait on FIV vaccination and retest the kitten at 6 months of age. It is also recommended that that kitten be isolated from other cats until it can be determined that the pet is truly negative for this disease.


  • Feline Immunodeficiency Virus is currently under-diagnosed.
  • Although males are at highest risk, female cats can also get this infection.
  • Bite wounds are the usual mode of transmission.
  • The sensitivity/specificity of the FeLV/FIV test is 98%.
  • Cats younger than 6 months that test positive for FIV should be tested again at six months of age.
  • Because incubation of the disease can take up to two months, it is recommended that cats be re-tested to make sure that they are truly negative for this disease.
  • If an asymptomatic cat tests positive for FIV, it is recommended to re-test 2-3 months later to verify persistent infection.
  • Vaccination with the FIV vaccine will result in a positive result on the currently used FIV antibody test.
  • Cats should be tested for FIV virus prior to vaccination. If cats test positive, wait to re-test in 2 months before beginning vaccination.
  • Indoor only cats who are not exposed to other outdoor cats do not need to be vaccinated for FeLV and FIV.
  • All outdoor cats should be periodically tested for FeLV and FIV so proper steps can be taken to minimize exposure to the general population.