Feline immunodeficiency virus, or FIV, is a virus in the same family as the human immunodeficiency virus (HIV) that causes AIDS, but it only infects cats. Like HIV in humans, FIV weakens the immune system, making it difficult for the animal to fight off other infections. This can lead to a wide variety of symptoms, such as weight loss, swollen lymph nodes, fever, and diarrhea. However, many cats do not show any symptoms at all.

While any cat can catch FIV, it is most common in outdoor cats that get into fights with other cats, or in kittens that become infected before birth or from their mother's milk after birth. It is not easily spread between cats sharing the same home.

Although it can be fatal if left untreated, a positive test for FIV is not a mandatory death sentence for your pet. With a high-protein diet and aggressive treatment of secondary infections, an FIV-positive cat can lead a reasonably normal life for a number of years after diagnosis.

What Is Feline Immunodeficiency Virus?

FIV is a retrovirus that only affects cats. It can be treated but not cured. As a result, cats with FIV are likely to have a shorter lifespan than healthy cats, but they can still be wonderful pets.

In the U.S., approximately 1.5 to 3 percent of healthy cats are infected with FIV. Most cats with FIV live outdoors and are thus more likely to experience bites from infected feral cats. FIV cannot be transmitted to human beings.

Once infected with the virus, cats go through three phases. In the first, called the acute phase, which occurs roughly one to three months after infection, the virus enters the cat's lymph nodes, and from there, penetrates white blood cells. These blood cells are a critical component of the immune system. During the acute phase, the cat might have swollen lymph nodes, a low-grade fever, lethargy, and loss of appetite. These symptoms can be very mild and easily missed by the cat's owner, however.

During the second phase, called the latent or asymptomatic phase, the virus very slowly replicates within the cat's immune system. However, the infected cat doesn't show outward signs of illness during this phase, although blood tests can be abnormal. The asymptomatic phase can last from months to years. Some cats never progress beyond this phase.

In the third phase, called the progressive phase, the cat's immune system declines greatly, allowing secondary infections to take hold. Urinary tract infections, skin infections, gum disease, cancer, and upper respiratory infections are all common during this phase, which is sometimes referred to as feline AIDS. Most cats only survive for a few months after reaching this phase.

Symptoms of FIV in Cats

Symptoms of FIV often don't show up until years after infection. The following are some of the most common symptoms in FIV-positive cats.

It can be difficult to spot FIV early on, because the symptoms, such as diarrhea, lack of appetite, and low-grade fever, can be mild and easily attributed to other causes. That's why it's so important to take your cat to the vet should it show several signs of illness that last more than a day or two, even if the symptoms are mild.

In cats that have progressed to full-blown feline AIDS, numerous secondary infections, as well as cancer, are common, although it's important to note that it isn't the FIV itself directly causing the symptoms. The breakdown of the cat's immune system caused by the FIV indirectly leads to the development of secondary health problems and
diseases.

Weight Loss

Because cats with FIV tend to lose their appetites, they usually lose weight. This can be one of the first symptoms you notice.

Disheveled Coat

Cats with FIV can look a bit ratty. This is partly because they don't pay much attention to grooming themselves when they don't feel good and partly because the various secondary diseases that underlie FIV often cause the skin and fur to be less healthy or even cause fur loss.

Lack of Appetite

Most cats in the early stages of FIV lose their appetites. You'll notice the food bowl stays full, or your cat stops eating after a few bites. In the last phase of the disease, your cat might once again stop eating due to a secondary infection causing pain, discomfort, or general malaise.

Diarrhea

In both the first and last phase of FIV, your cat might have soft or watery stools and might pass feces more often than normal. Most healthy cats have only one or two bowels movements per day.

Conjunctivitis

Conjunctivitis is redness affecting the whites of the eyes. It often occurs in cats who have progressed to the third stage of FIV, as they are prone to eye infections and eye inflammation. It it is not common in cats in the early stages of the disease.

Discharge from Eyes or Nose

Cats in the last stage of FIV are very prone to upper respiratory infections, which typically present with runny eyes or nose. The discharge can be watery or goopy and you might also see dried crusts around the cat's nose and eyes.

Changes in Behavior

Cats that don't feel well often become lethargic, meaning that they sleep more than usual or don't seem to have much energy. Your cat might also hide, have little interest in playing or being petted, become irritable, or just seem "off" in mood.

Urinating Outside the Litter Box

Urinary tract infections (UTIs) are common in cats that are in the late stage of FIV. Because UTIs are painful and cause the cat to need to urinate more often than normal, your cat might not make it to the litter box in time or might start associating the litter box with pain, thus causing the cat to urinate in other places around your home. You might also notice your cat strains to pass urine, due to the pain and inflammation of the UTI.

Causes of FIV

A cat generally develops FIV after being bitten by an infected feline, as the virus primarily sheds through the infected cat's saliva. When an infected cat bites a non-infected cat, the virus is injected directly into the non-infected cat's bloodstream. FIV can also be transmitted through direct contact with infected blood. It can also be transmitted from an FIV-positive cat to her kittens during birth or while nursing.

It's very rare for a cat to develop FIV by sharing food bowls or simply being around an FIV-positive cat, so there's no need to be worried if you have one cat in your household that's FIV-positive and another that's not. However, it's prudent to test all cats in the household if one is diagnosed is FIV, just to be sure.

Diagnosing Feline Immunodeficiency Virus in Cats

FIV is primarily diagnosed through a blood test called an ELISA test (enzyme-linked immunosorbent assay). A positive result means that the cat has produced antibodies to FIV and most likely is infected with the virus. However, it can take up to eight weeks after exposure for a cat to test positive, so it is possible to get false-negative results.

More commonly, a cat can have a false-positive result on the ELISA test if it was vaccinated against FIV, as the vaccination causes the cat to produce antibodies against FIV even though it isn't actually infected with the virus. Young kittens might also have a false-positive result if their mother was infected during pregnancy, as the mother's milk can transfer antibodies to the nursing kittens.

If your cat has a positive ELISA test, your veterinarian might recommend a second test that is more definitive, called the western blot test or PCR (polymerase chain reaction) test.

Treatment

Cats with FIV commonly live normal life spans as long as they are not also infected with feline leukemia virus. If your cat has been diagnosed as FIV-positive, work closely with your veterinarian to design a management program. Cats with FIV, whether or not they are displaying symptoms, have a weakened immune system so they should be closely monitored for secondary infections. In fact, it's the secondary infections that finally prove fatal to an FIV-infected cat.

For cats with no symptoms and in otherwise generally good health, a treatment program might simply be a matter of ensuring it gets a sound diet, possibly with added vitamins, antioxidants, and Omega-3 or Omega-6 fatty acids, as well as prompt, aggressive treatment of infections and other conditions as they crop up.

There's no cure for FIV, nor is there a specific medical treatment for the disease, even as the cat's health declines. A vet might try anti-inflammatory drugs, immune-enhancing drugs, and medication for secondary infections to keep the cat as healthy as possible, however.

Prognosis for Cats with Feline Immunodeficiency Virus

FIV-positive cats that don't progress beyond the latent phase generally do fairly well and with good care can live for many years. Cats that progress into the last phase, however, usually succumb to cancer or a secondary illness within a few months.

How to Prevent FIV

Outdoor cats are most at risk of acquiring the virus, so the best way to prevent infection with FIV is to ensure that your cat stays indoors. Avoid contact with other cats known to have FIV, as a bite can lead to infection. Spay or neuter your cats, as intact cats, especially males, are more prone to outdoor wandering and fighting.

Although there was a vaccine for FIV at one time, it was removed from the North American market in 2016 due to concerns about false-positive results and lack of efficacy.

Is FIV Contagious to Other Animals?

The feline immunodeficiency virus is only contagious to cats. Humans, dogs, and other pets cannot catch FIV from an infected cat. However, an FIV-positive cat can spread the virus to other cats.