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Feline Immunodeficiency Virus (FIV) and Feline Leukemia Virus (FeLV) ... What's the Difference?

feline diseaseThe feline immunodeficiency virus or FIV is a very common infectious disease. It is estimated three percent of healthy cats in the U.S. and 14 percent of cats with health problems have the virus.

FIV is most prevalent in intact males that roam free outdoors and fight with other cats. Bites from infected cats are the primary mode of transmission. That’s why keeping your cat indoors is the best way to avoid the virus.

According to the

Feline AIDS works much like the human variety, weakening cats' immune system and making them susceptible to infections of the skin, eyes, nose, mouth and urinary tract as well as more serious ailments like cancer and kidney failure. The disease typically stays latent for years, with cats becoming ill later in life.

FIV is frequently confused with the feline leukemia virus (FeLV), which also attacks the immune system. But FeLV can be spread through casual contact between cats, and while cats with FIV can have normal life spans, those with FeLV often die within three years of becoming infected.

Dr. Becker's Comments:

As the article points out, FIV is very often confused with FeLV. Both diseases belong to the same retrovirus family. A retrovirus is a ribonucleic acid (RNA) virus with a reverse transcriptase enzyme that allows the genetic information of the virus to become part of the genetic information of the host cell upon replication.

FIV and FeLV cause many of the same secondary conditions, but they are different in many ways. Most telling -- FIV can be considered a 'life sentence' of sorts, while feline leukemia is, unfortunately, usually a death sentence.

Feline Immunodeficiency Virus (FIV)

FIV is classified as a lentivirus, or a 'slow virus,' meaning it has a long incubation period.

The virus is transmitted primarily through bite wounds. The infection can also be passed from an infected mother cat to her kittens during birth or feeding, but this is a relatively rare event, as is transmission through sexual contact.

FIV is a feline-specific virus, so you don't need to be concerned about catching the disease from your cat.

If your cat has contracted the virus, you may not know it for years. Eventually, though, the infection can create immune deficiency and your kitty's body won't be able to adequately defend against other infections.

Everyday environmental pathogens that don't affect a healthy animal can cause serious illness in a cat with a compromised immune system. It is these secondary infections that cause a lot of the diseases we see in FIV-positive kitties.

Symptoms of FIV

Early in an FIV infection, there can be temporary enlargement of the lymph nodes, often with fever. But you may not even notice this stage of infection unless the lymph nodes are noticeably enlarged.

Some FIV-positive cats experience a progressive deterioration of their health. Others have recurring illness in between periods of apparent good health. Signs of immunodeficiency often don't appear for years after infection. They can show up anywhere on your pet's body and can include:

  • Persistent fever and loss of appetite
  • Inflammation of the gums and mouth
  • Chronic or recurrent skin, bladder and upper respiratory tract infections
  • Seizures, changes in behavior and other neurological symptoms
  • Persistent diarrhea
  • Oral infections, stomatitis, gingivitis
  • Poor coat condition
  • Eye problems
  • Slow weight loss initially, followed by severe wasting later in the disease
  • Reproductive failure and abortions in intact cats
  • Cancers and blood diseases


An antibody test will be performed by your vet to see if there are antibodies to the virus present in your cat's blood. The presence of antibodies indicates FIV infection. However, false-positives do occur, so many veterinarians confirm initial positive results with a different test.

Kittens born to FIV-positive mother cats often test positive for several months after birth. Fortunately, few of these babies are actually infected. FIV-positive kittens younger than six months should be retested about every 60 days until at least the age of six months.

An FIV-negative test result generally means the cat is not infected. However, since it takes eight to 12 weeks (and sometimes longer) after infection for measurable levels of antibodies to appear, there is a chance a cat that tests negative is actually incubating the virus.

If you know or suspect your kitty might have been exposed (bitten, most likely) by an FIV-infected cat, or even an unknown cat, you should have your pet retested 60 days after exposure.

Rarely, a cat in the late stages of FIV infection can test negative. This occurs when the immune system is so compromised it can no longer produce detectable levels of antibody.

Caring for an FIV-Positive Cat

If your kitty is diagnosed with FIV, she should be kept indoors. This will prevent spread of the virus to cats outside your home, and will reduce the risk your pet will be exposed to pathogens that her immune system can't defend against.

If you haven't already, you should spay or neuter your FIV-positive cat.

Feed your kitty a balanced, nutritionally complete, species-appropriate diet. Raw diets are fine, with one exception. The only time I recommend a cooked fresh food diet is if a cat's white blood cell (WBC) count is also affected (low). Most of the FIV-positive cats in my practice have completely normal bloodwork, except for being viral positive.

I recommend at least twice yearly wellness checkups with your holistic vet for FIV-infected cats. The vet should check the health of your pet's eyes, gums, skin and lymph nodes, as well as her weight. At one of the two yearly visits, a complete blood count, urinalysis, and serum biochemical analysis should be ordered.

I also recommend you perform routine at-home wellness exams in between vet visits. Careful, consistent monitoring of your FIV-positive pet's health and behavior is extremely important so you can notify your vet right away if anything changes.

Talk with your holistic vet about what medications and alternative therapies might be beneficial for your kitty. Treatment, when appropriate, will depend on symptoms, the age of your pet, her general health and other factors.

At my practice, we use a variety of natural supplements to bolster the immune systems of FIV-positive cats, including Standard Process Feline Immune System Support, Thorne Moducare, turmeric, thymus extracts, Chinese herbs and FIV homeopathic nosodes. We have very good success keeping FIV-positive cats very healthy.

Many cats with FIV live normal or near-normal life spans with good quality care. But it's impossible to predict how long or how well your cat will survive after diagnosis. Cats that develop serious illnesses secondary to an FIV infection have a less hopeful prognosis, as do kitties with persistent fever and progressive weight loss.

The good news is an FIV infection should not be a death sentence for your cat. This virus degrades the immune system over time, so proactive care can allow FIV infected cats to live a completely normal life, in most cases.

My clients with FIV-positive cats view it as a challenge to work on strengthening their pet's immune system and helping their kitty live as healthy a life as possible.

Feline Leukemia Virus (FeLV)

The number of U.S. cats with FeLV is similar to FIV statistics – about three percent of healthy cats are infected with FeLV and 13 percent or more of very young and ill cats.

Cats with a persistent FeLV infection are heavy transmitters of the disease. The virus is shed in saliva, nasal secretions, urine, feces and milk from infected mother cats.

Cat-to-cat transfer can also occur from the bite of an infected cat and during mutual grooming. Rarely, the shared use of litter boxes and food and water bowls can transmit the infection.

Mother cats can transfer the virus to her kittens in utero or during nursing. Fortunately, the virus doesn't live long outside the host's body – generally less than four hours in a normal household.

Cats most at risk of acquiring the infection are those living with infected cats, cats roaming around free outdoors who can be bitten by an infected cat, and kittens born to mothers with the infection.

Kittens are at much higher risk than adult cats, but fortunately, maturity brings increasing resistance to the virus. However, healthy adult cats can become infected given adequate exposure.

There's no scientific evidence that FeLV can be transmitted from your cat to you. However, FeLV-positive cats are at higher risk of  carrying other diseases. It is generally recommended that the very young, the very old, women who are pregnant and people with suppressed immune systems avoid contact with FeLV-infected kitties. However, I have many FeLV positive cats in my practice and I have never had any incidence of human health related issues in their homes.

How FeLV Affects Cats

The feline leukemia virus is the most common cause of cancer in cats. It also plays a role in blood disorders and like FIV, can lead to a weakened immune system and secondary infections.

In the early stage of an FeLV infection, similar to an FIV infection, your cat may show no symptoms at all. But over time – weeks to months to even years – your pet's health will gradually deteriorate. Or, he might have periods of relatively good health interspersed with recurring secondary illnesses.

The symptoms of FeLV are identical to those seen with an FIV infection (see list of symptoms above).

There are actually two stages of a feline leukemia virus infection:

  • Primary viremia (viremia is the condition of having FeLV present in the bloodstream) is the early stage of the infection. During this stage, the immune systems of some cats are able to respond sufficiently to wipe out the virus and stop progression of the disease.
  • Secondary viremia is the later stage during which there is persistent infection in bone marrow and other tissue. If FeLV reaches this stage in your cat, he'll very likely be infected for the remainder of his life.

Diagnosis and Management of FeLV

Your vet will use either an ELISA (enzyme-linked immunosorbent assay) or similar blood test or an IFA (indirect immunofluorescent antibody assay) blood test to diagnose your pet. The IFA test picks up secondary viremia only, so if your cat tests positive, the infection will be with her for the remainder of her life.

Caring for your FeLV-positive kitty should be along the same guidelines listed above for an FIV-infected cat.

Some of the alternative products I use with FeLV cats include:

  • Standard Process Feline Immune System Support
  • Feline Whole Body Support
  • Thorne Moducare
  • Turmeric
  • IV vitamin C therapy
  • Chinese herbs
  • FeLV homeopathic nosodes

We have very good success at Natural Pet keeping FeLV-infected cats who have not yet expressed symptoms of the disease asymptomatic.

I'm very sad to say the vast majority of FeLV-positive cats whose immune systems are not supported die from a secondary disease within two or three years of acquiring the infection. As is the case with FIV kitties, if your pet has already endured one or more serious FeLV-related illnesses, or has a persistent fever and weight loss, or if cancer has developed, a much shorter survival time can be expected.

The goal is to identify these diseases before cats become symptomatic and offer lifetime immune system support. In these cases, many viral positive cats can live a completely normal life as long as their immune systems continue to be supported and maintained.

Keeping Cats Safe from FIV and FeLV Infections

The only guaranteed way to keep your cat safe is to prevent exposure to these viruses.

Keep your cat indoors, away from potentially infected cats. If you want to let your pet outdoors in nice weather, either provide constant supervision or make sure he is safe in an enclosure he can't get out of, and no other cat can get in to. Also make sure no one can be bitten through the sides or top of the enclosure.

 If you have an uninfected kitty at home, don't even consider bringing an untested cat home from a shelter or rescue organization and allowing the two cats to share living quarters before you know the health status of the new kitty.

I know of many instances of FIV positive and negative cats living in the same house, without disease transfer. The key is to prevent cat fights (biting), which is how the virus is spread. So if you choose to blend FIV positive and negative cats in one house, make sure everyone is spayed or neutered and introduce them slowly to avoid bite wounds.

House FeLV-positive cats separate from viral-free cats.

There are vaccines available now for both FIV and FeLV. I'm not in favor of either – especially the FIV vaccine. They are often not effective in protecting against the viruses, and they are implicated in the development of vaccine-associated sarcomas.

A further drawback is after receiving either vaccine, your cat will develop antibodies to the virus. Sadly, many shelters immediately euthanize any cat that tests positive for FIV or FeLV antibodies.

Indoor-only cats have little to no exposure to cats infected with these viruses. I strongly urge you to simply keep your cat inside, and build or purchase a secure enclosure to put on your porch, patio or outdoor deck if you want to get kitty outdoors in good weather.

The UC Davis William R. Pritchard Veterinary Medical Teaching Hospital recommends the FeLV vaccine only for uninfected cats allowed to go outdoors or cats that have direct contact with other cats of unknown FeLV status (high-risk animals). And due to vaccine-related sarcoma concerns, they only carry the recombinant transdermal vaccine and avoid killed, adjuvanted vaccines.

As for the FIV vaccine, they don't even stock it and don't recommend it for indoor-only cats.

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