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Feline Immunodeficiency Virus (FIV): Symptoms, Prevention, and More

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Eirevet is a veterinarian specialized in canine and feline internal medicine who owns a small animal veterinary hospital in Ireland.

Outdoor cats are at greater risk of contracting FIV.

Outdoor cats are at greater risk of contracting FIV.

FIV: Some Background Information

Feline Immunodeficiency Virus (FIV) is a retrovirus that is closely related to the human HIV virus. However, it does not pose a risk to human health, as it is species-specific. The virus was first identified in the mid-1980s in California, but it quickly became apparent that it is found worldwide.

Different strains or 'clades' of the virus are recognised, and their prevalence varies internationally, with subtype A being the most common in the UK and Ireland, and subtype B being more common in the United States. This information is useful to bear in mind when we later discuss vaccination against the disease.

How Is FIV Transmitted?

Infected cats shed infectious FIV particles in bodily secretions, and experimental studies have documented infection through various routes. However, 'natural' infection usually only occurs through biting, with the infected saliva transmitting virus into the victim's bloodstream. Therefore, infection is most common in outdoor entire male cats, and other outdoor cats that become involved in aggressive disputes over territory or other 'assets'. The lower risk of FIV infection is one of many reasons why it is advisable to have your cat neutered.

Although only around 1 in 25 cats (on average) in any given population are infected with FIV, it has been shown that around 1 in 6 cats that have suffered a cat bite wound will subsequently test positive.

Structure of a Retrovirus


How Does FIV Cause Illness?

Following infection, the virus is attacked by cells of the immune system. However, rather than overcoming the infection, these cells become the hosts for the FIV virus. It replicates in a particular type of cell called a T-lymphocyte, which is responsible for regulating the immune system. These T-lymphocytes are found throughout the body, and during the first few weeks of infection, lymph node enlargement may be detectable. The lymph nodes are structures containing large numbers of lymphocytes, which are found at various locations including under the jaw, in front of the shoulder joints, and between the bellies of the calf muscles in the hind legs.

The infected cat may display mild signs of illness during this phase, ranging from fever to inappetence, or signs may not be noticed at all. The vast majority of cats will then experience a very long asymptomatic phase while the virus 'quietly' resides in its host cells. However, even during this 'asymptomatic' phase, immune function is declining as the virus has a negative effect on the infected T-lymphocytes.

Many FIV-infected cats will leave reasonably healthy lives for years before developing signs of severe immunodeficiency. However, they will often require more aggressive treatment of minor illnesses, for example prolonged antibiotic courses, for relatively minor ailments in the interim.

FIV Blood Test Kit

In-house testing for FIV is quick and simple, and it should be performed on every cat with a history of being bitten.

In-house testing for FIV is quick and simple, and it should be performed on every cat with a history of being bitten.

Symptoms of FIV Infection in Cats

Most of the signs seen are not caused directly by the FIV virus, but are rather the result of a malfunctioning immune system. Immunity in a healthy animal is a careful balance between tolerance of non-harmful agents such as the animal's own cells, and recognition & elimination of harmful agents (pathogens). Because of the multiple roles T-lymphocytes normally play, illness in FIV can result from either a loss of tolerance, or a failure to effectively recognize and eliminate infectious organisms or cancerous cells.

While testing specifically for the virus using a kit such as that shown above is a very sensitive way of detecting infection, other findings on routine blood and other screens are non-specific and will not yield a diagnosis, so it is vital your veterinarian is suspicious of FIV in any cat with an unusually severe or recurrent form of any illness.

Gingivitis/stomatitis, a common condition causing severe mouth pain, is commonly seen in conjunction with FIV. It should also be ruled out in any cat with chronic rhinitis or flu symptoms. Unexplained weight loss or lymph node enlargement may also be seen.

Changes in behavior, seizures, and disrupted sleep patterns are common neurological symptoms, and FIV infection is also a cause of sterility in breeding animals.

Preventing FIV: Vaccination

While an FIV vaccine has been available in many parts of the world for some time now, it remains the subject of some controversy in veterinary circles for a couple of reasons. The vaccine is reasonably effective, preventing infection in about 4 out of 5 vaccinated cats that are exposed to the same subtype of the virus, and this is part of the problem; while the vaccine protects against the majority of strains found in North American cats, it is ineffective against strains found in Europe. For this and other reasons, the vaccine is not licensed for use in European countries.

The other issue with the vaccine is that it can lead to difficulties in assessing whether an animal is infected or not later in life. Even in a vaccinated cat, there is still a chance that he/she can become infected later in life. FIV blood tests performed by veterinarians measure antibody levels against the virus, and at present there is no reliable way to distinguish between an animal that has high antibody levels due to vaccination and one which has been infected by the FIV virus.

The situation is even more difficult when dealing with a stray cat that is being taken in by a rescue organisation or an individual, for in these situations we would like to test the incoming cat for infectious diseases. If the cat tests positive for FIV we have to consider the possibility that this was a previously owned pet who was vaccinated against FIV, and we are now unsure as to his/her FIV status. A real conundrum, and one to which we don't yet have a solution.

Your Relationship With Your Veterinarian

If you have an FIV-positive cat, you are both certainly going to rely on a lot of input from your veterinarian over the years. I am strongly of the opinion that if your vet does not have a positive outlook about managing your cat's health, or indeed advises that you euthanize your cat at the time of diagnosis despite your cat being otherwise in good health you should find a new vet.

Your Cat Is FIV Positive: What Now?

FIV is NOT a death sentence. While the FIV virus itself is resistant to treatment, the illnesses caused by the immune deficiency are not. It is important your veterinarian knows the FIV status of your cat in order to formulate appropriate treatment plans, which generally need to be more intensive and more prolonged than those in an FIV negative patient with similar symptoms. However, an FIV positive status must never be used as a reason not to pursue diagnostic investigations or treatments.

There have been several 'false dawns' in the pursuit of antiviral treatments effective against FIV. While there have been some published reports of effective treatment of the virus with human anti-retroviral drugs (eg AZT) used in the treatment of HIV and AIDS, any antiviral benefit is outweighed by negative effects on the patient such as anemia. In any case, with careful management of any secondary problems such as gingivitis or chronic flu symptoms, most FIV-positive cats can enjoy a good quality of life for almost as long as an FIV-negative patient.

Where to Find a Good Cat Veterinarian

Routine Health Care of Cats With FIV Infection

As well as being susceptible to viral and bacterial infections, your cat is more likely to develop heavy burdens of parasites, even with a lower level of exposure. Hands, feet and clothing can easily carry fleas or worm eggs or larvae from outdoors, and regular deworming and flea treatments are essential.

Cats with FIV should never be fed raw meat as they are much more likely to suffer acute food poisoning, or infection with toxoplasma which can lead to serious illness or death. A balanced, good quality commercial cat food is the best diet for most cats, but especially those with immunodeficiency.

Vaccinations for FIV Positive Cats

While there has been some controversy about vaccinating an FIV-positive cat against the common diseases, notably the flu viruses and panleukopenia virus, FIV-positive cats that are generally well do respond well to vaccination. They show appropriate increases in antibody levels after vaccination which are protective against these illnesses.

However, there is a possibility that vaccination may promote viral replication through T-lymphocyte stimulation. This seems to be a theoretical concern which has not been borne out through research to my knowledge, so in general most feline practitioners would recommend vaccination except in exceptional circumstances where the owner can guarantee that neither they nor their cats will be in contact with other cats.

The most common route for the spread of most feline viral diseases is not direct contact between cats, but rather on fomites such as hands and clothing. Speak to your veterinarian to assess your cat's individual risk of contracting disease.

Want to Know More? A Detailed Presentation on FIV

Be a Responsible Owner

Unfortunately, you need to consider your FIV positive cat a risk to other cats. FIV is essentially a disease passed on through aggressive behavior, and as such there is a low risk of transmission between cats in a 'stable' household with the introduction of no new pets, and no major upheavals (eg moving home, having an elderly relative moving in). In the event of a major stress within the house, tempers may flare, and inter-cat aggression may become a problem.

Should I Separate My FIV-Positive Cat?

However, I do not usually advise my clients to separate their FIV-positive cats from the negative ones within the house. If a stress such as those mentioned above can be anticipated, then taking steps such as using Feliway to reduce aggression are advisable.

Of course, as well as the risk from your cat, your FIV-positive kitty is also more susceptible to contracting other illnesses from cats outdoors. This risk is also obviously eliminated by preventing his/her contact with cats of unknown health status.

Should I Let My FIV-Positive Cat Outside?

While the risk to the other cats in your home may be very low, the same cannot be said for other cats your pet encounters outdoors. Territorial aggression is very likely to result in biting behavior, and even a relatively passive cat could potentially find themselves in a situation where they bite another animal, and thereby pass on this incurable illness.

For this reason, the only responsible way to manage your cat with FIV is to make him/her an indoor-only cat. This may be a huge challenge, but one cannot knowingly put somebody else's beloved pet at risk of contracting a long-term illness.

If your cat has been used to having outdoor access, then it is vital that you try to replace some of the stimulation which outdoor living provides within the confines of your home. Climbing trees, laser pointers, and robotic mice are just a few of the things you can provide to make your home more stimulating and cat-friendly.

What Does It All Mean?

If you take nothing else from this article, I do want to convey that FIV is not a terminal illness. I have had more than one patient with FIV infection that lived beyond twenty years of age. With dedication from the owner, plenty of input from a committed veterinarian, an enriched environment, and good quality nutrition, your cat can live a long, healthy, and happy life.

Please use the comments section below if you would like to leave a message or have any questions regarding your cat.

Quality of Care for Cats With FIV

This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

© 2015 eirevet

Comments on FIV in Cats

Sharon Licon on April 16, 2019:

Im so glad I read these articles on FIV. My 11yr.old cat Fluffy tested positive for it. Ive been so afraid for my other cats that I havent wanted them to be anywhere near him or drink out of the same water dish. My vet said it wasnt contagous, but didnt explain how it spreads. Now I know more and am feeling so much better.