FeLV and FIV in Cats: Feline Leukemia and Immunodeficiency Virus

By Tailwisp Editorial TeamUpdated October 20, 20264 min read

Feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV) are two of the most important infectious diseases of cats. Both weaken the immune system, and both are often mentioned in the same breath. They are different viruses with different risks, and a positive test is not always a death sentence, especially with FIV.

What are FeLV and FIV?

Both are retroviruses that infect immune cells. They do not infect humans or dogs.

FeLV can cause anemia, immune suppression, lymphoma and other cancers. Some cats clear the virus, some become carriers with no signs and others develop progressive disease.

FIV is similar to HIV in humans in how it attacks immune cells, but it does not spread to people. Many infected cats remain healthy for years, and eventually some develop immune problems.

How they spread

FeLV passes in saliva, nasal secretions, urine and milk. Spread occurs through close, prolonged contact such as mutual grooming, shared bowls and litter boxes, and from mother to kittens. Young kittens are most vulnerable.

FIV spreads mainly through deep bite wounds, so it is more common in unneutered outdoor male cats that fight. Casual contact, such as sharing bowls, rarely spreads it. See aggression between cats.

Signs

Many infected cats show no signs at first. As disease progresses, signs may include:

• Weight loss and poor appetite
• Pale gums, from anemia
• Fever and lethargy
• Recurring infections, such as upper respiratory disease. See upper respiratory infections in cats.
• Dental disease and mouth inflammation. See cat dental disease.
• Swollen lymph nodes
• Diarrhea or skin problems
• Cancers, particularly lymphoma, in FeLV

Testing

A quick blood test, usually performed in the clinic, screens for FeLV antigen and FIV antibodies. Positive results should be confirmed with a second test, since false positives happen, especially in low-risk cats and kittens. Kittens under six months can test positive for FIV from maternal antibodies and should be retested.

Test:

• All new kittens and adopted cats, before introducing to other cats. See adopting a cat from a shelter.
• Sick cats
• Cats exposed to infected cats or bitten
• Outdoor cats, on a regular basis

Living with a positive cat

FIV-positive. Many cats live long, normal lives with good care. They can often share a home with FIV-negative cats if they do not fight, since the virus is not spread by casual contact. Keep them indoors, neutered and on a good diet.

FeLV-positive. Prognosis varies. Some cats live for years, but many develop illness within a few years of diagnosis. Keep them away from uninfected cats, indoors, and watch for changes.

Both need:

• Regular vet checks, often twice a year
• Prompt treatment of infections
• Good nutrition. See how to read a cat food label.
• Parasite control and dental care
• Limited stress. See cat-friendly home setup.
• Avoiding raw food, which carries infection risk. See raw food diets for cats.

Treatment

There is no cure for either virus. Care focuses on supportive treatment, managing infections and, for FeLV-related cancers or anemia, specialist care. Some antiviral drugs and immune modulators are used in certain cases. Your vet will advise.

Prevention

• Vaccinate against FeLV. Recommended for all kittens and for adult cats at risk, such as those that go outdoors. See cat vaccination schedule.
• Keep cats indoors to prevent fights and exposure. See how to build a catio.
• Neuter your cat. This reduces fighting and roaming. See when to spay or neuter a kitten.
• Test before adding a cat.
• Quarantine new arrivals until tested.

There is no FIV vaccine currently available in the US, so avoidance is the main protection.

Adopting an infected cat

Many shelters and rescues place FIV-positive and FeLV-positive cats. With good care, a positive cat can be a loving companion. Discuss the cat's health history, expected costs and the other animals in your home with the rescue and your vet before deciding. See adopting a cat from a shelter.

Retesting

A cat that tests negative may still be incubating the virus if it was exposed recently. Retest about two to three months after a possible exposure, and keep new cats separate until the second test is clear. Vaccinated cats can still be tested for FeLV, because the vaccine does not cause a positive antigen test.

When to see a vet

See a vet for testing when you adopt a cat, and for any signs of illness. Use the US vet directory to find a clinic, and see cat vet visit costs.

This article is general educational information, not veterinary advice. Every cat is different. If your cat is unwell, or you are unsure about a symptom, diet change or medication, contact your veterinarian.