Feline Aids (FIV): Causes, Symptoms, & Treatment

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Feline AIDS featured image cat lying on the floor

What Is Feline Aids (FIV)?

Feline AIDS (Feline Acquired Immune Deficiency) Syndrome) is a disease caused by  FIV (Feline Immunodeficiency Virus). As the name suggests, the syndrome has parallels with Human AIDS, caused by the Human Immunodeficiency Virus (HIV).

How Common Is Feline Aids?

Feline AIDS is common all around the world, but its prevalence varies from location to location. For example, in a 2017 study of cats in the USA and Canada, 3.6% of cats were positive. Cats that present as sick animals have a higher chance of being FIV positive (e.g. in the 2017 study, nearly 10% of cats with oral disease were FIV positive).

Similarly, in the UK, between three to six percent of healthy cats are positive, while sick cats tested while visiting vet clinics have a  higher prevalence of 12 -18%.

FIV infection is more common in intact (uncastrated) male cats that have a history of deep bite wounds or abscesses, or that spend time outside.

What Causes Feline Aids?

Feline AIDS is caused by Feline Immunodeficiency Virus (FIV). FIV is a retrovirus belonging to the lentivirus genus. The virus causes generalised immunosuppression, depleting specific white blood cells (T-helper cells).

This depletion in white blood cells has a strong negative effect on the cat’s immune system, making the cat more susceptible to infections and illness.

How Is Feline Aids Transmitted?

The FIV virus causing Feline AIDS is mainly passed from cat to cat in the saliva via bite wounds.

The virus may also be transmitted from pregnant females to their offspring in the womb, or in early life via the milk. Rarely, the infection may transmit between two cats in the same household that have no history of fighting or biting each other.

Is Feline Aids Contagious To Humans?

No. FIV, causing Feline AIDS, and HIV, causing Human AIDS, are both lentiviruses, but humans cannot be infected by FIV, nor can cats be infected by HIV.

What Are The Symptoms Of Feline Aids?

Lethargic cat lying on floor feline AIDS

Cats with Feline AIDS exhibit symptoms related to immunosuppression, including lethargy, inappetence, and fever.

The symptoms of Feline AIDS are linked to immunosuppression, which enables secondary infection by other disease-causing agents.

Typical Early Signs Include:

  • Lethargy
  • Inappetence
  • Fever
  • Lymphadenopathy (enlarged lymph nodes)

In the later stages of the disease, a range of serious signs of disease are seen, including:

  • Gingivitis and stomatitis with halitosis, drooling, and pain when eating
  • Weight loss
  • Abscesses
  • Respiratory signs (such as wheezing and dyspnea)
  • Neurological signs (such as behavioral changes and seizures)
  • Ocular issues
  • Digestive disorders

In addition to these issues, feline AIDS is connected to a wide variety of other intercurrent infections.

Cat FIV Stages

Three Stages Follow FIV Infection.

1.The Primary Phase. This stage includes the first two to four months after infection with the virus. Some infected cats are asymptomatic, while other FIV cats show short-term signs of illness involving malaise, pyrexia, and possibly generalised lymph node enlargement. Most FIV positive cats recover from this early phase.

2. The Second Phase, sometimes known as the latent stage. During this stage, cats show no signs of illness, living healthy lives for months or years.

3. The Third Phase known as the Feline Acquired Immunodeficiency Disease stage (FAIDS). The signs shown may depend on where in the cat’s body the virus is active.

Infection of the nervous system can lead to neurological signs or behavior change, infection of the digestive system can lead to chronic diarrhoea. The most prominent signs are usually linked to the overall immunodeficiency caused by the virus, with signs including weight loss, inappetence, fever, lymphadenopathy (enlarged lymph nodes) and gingivitis.

Other typical problems include upper respiratory tract signs such as rhinitis (inflammation of the lining of the nose) and conjunctivitis, as well as repeated problems with skin infections. Affected cats are also at a higher risk of developing cancer (e.g.  lymphoma) as well as multiple other infections that would not cause significant problems in cats with healthy immune systems.

How Long Do Cats Live With Feline Aids?

The prognosis for cats that are FIV positive, but without showing signs of illness, can be very good, with some cats living for almost as long as cats that are FIV negative. However, cats that have developed Feline AIDS, with severe signs of disease, have a poorer prognosis.

Their remaining lifespan may be just a few months, but with the right treatment, this may be extended to several years.

How Is FIV Diagnosed?

Feline Immunodeficiency Virus is diagnosed by carrying out a blood test, with various options available.

Most tests that are carried out in-house by veterinarians are antibody tests, based on enzyme-linked immunosorbent assay (ELISA) or immunochromatographic (IC) techniques to detect FIV antibodies.

These tests are accurate, with high specificity and sensitivity. They can be processed rapidly, with the cat carer often waiting to hear the result within minutes. Often combination tests are used, with the blood sample being checked for Feline Leukemia Virus (FeLV) at the same time as FIV, which makes logical sense since the signs of both viral infections can be similar.

Positive results may be followed up by sending samples to external laboratories, which offer more specialised tests.

These are often used to doubly confirm a positive or negative diagnosis. Specialised tests include immunofluorescence (IFA) and western blot tests for the detection of antibodies to FIV, and virus isolation and polymerase chain reaction (PCR) for the detection of the virus itself.

Virus isolation is sensitive but needs specialised facilities, making it costly and slow compared to other diagnostic tests, so it’s rarely used.

PCR tests are now widely available, detecting the FIV nucleic acids. These are especially useful in the diagnosis of FIV infection in young kittens where antibodies derived from the infected mother cat may interfere with tests that use antibodies to make the diagnosis.

Feline Aids Test

Feline AIDS describes the disease caused by the FIV virus, so there is no specific test for AIDS. If a cat with signs of AIDS has a positive test result for FIV, then they would be classified as being positive for Feline AIDS.

How to Treat Feline AIDS

Cat carers should work closely with their DVM veterinarian to devise an individualised treatment strategy, but some of the following treatments may be used.

  • Zidovudine (AZT) blocks the viral reverse transcriptase enzyme, inhibiting infection of new cells with the virus, but it cannot decrease viral multiplication in cells that are already infected. AZT is most useful as a way of preventing cats from developing full-scale Feline AIDS, as well as for treating cats with neurologic disease or gingivostomatitis.
  • Interferon has been used, with its immunomodulatory and antiviral effects improving survival rates in some studies, while other studies have had less convincing results.
  • Lymphocyte T cell immune modulator (LTCI) stimulates the immune system and may be able to improve clinical signs and reduce the viral burden in affected cats.
  • Insulin, administered intra-nasally, has been linked to improvement in some cats affected with neurological signs of Feline AIDS.
  • General supportive therapy has a strong role to play, using antibiotics for bacterial infections, avoiding immunosuppressive medication like glucocorticoids, and perhaps erythropoietin to stimulate red blood cell production in anaemic cats. Blood transfusions may also be recommended in some cases.

How to Prevent Feline AIDS

Indoor cats, kept as single pets, have no risk of picking up FIV or Feline AIDS. Neutering plays a role in prevention, as neutered male cats are 80% less likely to fight compared to entire male cats.

Spread is by direct cat to cat contact by fighting, rather than via the environment (e.g. via food bowls or a litter box) or aerosols. The FIV virus is easily destroyed using common detergents and disinfectants, and it does not live for long in the environment.

If a new cat is introduced to a household, it makes sense to carry out an FIV test first.

Cats that are known to be FIV positive should be kept indoors to prevent the spread of infection to other cats, as well as to reduce exposure of themselves to other infectious diseases. Effective parasite control, regular vaccination and high-quality nutrition are all important to reduce the onset of signs linked to a poor immune system.

Feline AIDS Vaccine

Feline AIDS vaccine injection at vet's office

At-risk cats may be given the feline AIDS vaccine, which addresses two types of FIV.

A whole virus, adjuvant vaccine against FIV is licensed in the United States. This vaccine contains inactivated subtypes A and D. Efficacy is variable. The vaccine does not contain subtype B, which is one of the predominant subtypes found in the USA. Inconsistent results have been found in challenge studies.

FIV vaccine is considered a non-core vaccine by the American Association of Feline Practitioners (AAFP) and may be reserved for cats with at-risk lifestyles (e.g. those living with FIV-positive housemates, outdoor cats that are prone to fighting). 

Cats over 8 weeks can be vaccinated, using two doses given subcutaneously 2-3 weeks apart, followed by annual booster vaccinations. Cats vaccinated with the FIV vaccine will test positive on serologic tests, so they need to be identified (eg with a microchip) so that it is known that they are vaccinated, and they are not mistaken as being FIV positive due to virus exposure.

Feline AIDS is a complex disease that’s now well understood.

The diagnosis of an FIV positive blood test is no longer a reason to euthanase a healthy cat, as many positive cats can have long and healthy lives.

About Dr. Pete Wedderburn, DVM

Dr Pete Wedderburn qualified as a vet from Edinburgh in 1985 and has run his own 4-veterinarian companion animal practice in County Wicklow, Ireland, since 1991. Pete is well known as a media veterinarian with regular national tv, radio and newspaper slots, including a weekly column in the Daily Telegraph since 2007. Pete is known as "Pete the Vet" on his busy Facebook, Instagram and Twitter pages, regularly posting information on topical subjects and real-life cases from his clinic. He also write a regular blog at www.petethevet.com. His latest book: “Pet Subjects”, was published by Aurum Press in 2017.

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