The Difference Between FeLV and FIV (Feline leukemia virus & Feline immunodeficiency virus)


by Jessica Vogelsang, DVM


Of all infectious diseases in cats, few are as feared as FeLV and FIV—and with good reason.

Between 2-4% of feline population in the U.S. harbors one or both of these potentially fatal viruses. Many clinics use an in-house test that checks for both viruses at the same time, and most wellness conversations about infectious disease covers both topics, so it’s easy to see why owners might confuse the two. But while they are similar, there are some important differences in both transmission and how the virus works in the body.

Does my Indoor Cat Need Feline Leukemia Vaccine?

Does your cat need leukemia vaccine if she never goes outside? Country vet Dr. Rob Sharp has the answer.

If this were a yes-or-no question, the answer would be no. Feline leukemia, a usually fatal cancer caused by a retrovirus, spreads from cat to cat via saliva, when the animals lick, bite, or groom one another. Provided Piper never ventures outside and has no interaction with other cats, then there’s virtually no way she could contract the disease–and vaccinating her would be unnecessary.

Unfortunately, the real world rarely plays out in black and white, and there are many unexpected ways your pet could come in contact with another feline who has the virus. You might, for instance, leave Piper at a boarding facility during your vacation and later learn that she became friends with the kitty in the next cage.


FIV in Cats FAQs: Feline Immunodeficiency Virus Information

What is FIV?

FIV stands for feline immunodeficiency virus. FIV typically causes a weakening of the cat’s immune system. It is the same class of virus as HIV (a lentivirus); however, only cats can get FIV. People and dogs cannot.

How do cats get FIV?

The most common route of infection is a deep bite wound from an FIV-positive cat to another cat. It can also be transmitted via blood, in utero and from the milk of an infected mother cat. It is very rare for cats to get FIV just from being around infected cats, sharing food bowls, or from a person touching an FIV-positive cat and then touching an FIV-negative cat. Many FIV-positive cats and FIV-negative cats live together in the same home for years without spreading the virus to the non-infected cats. continued

What is FIV? Cat Salsa FIV+ Born 2010


What is FIV?

How Is FIV Diagnosed?


A simple blood test called ELISA is used to diagnose FIV. It is often routinely given to cats as they are admitted to animal shelters. Particularly if they are injured.


However, the test itself has a fundamental problem — it does not measure the actual virus, as most people believe. Instead, it merely records the presence of antibodies to the virus.


Antibodies are microscopic organisms that actually fight the virus. Due to many “false positive” results (20% and up) from this test, if a cat tests positive it should be retested later. That is very rarely done because of the cost. Killing is cheaper.