Look-alike Viruses: Why FIV and FeLV Are Not the Same

Author: Sean Ladd, March 2026

Many of you are very familiar with a virus named human immunodeficiency virus or HIV. Well, there is a similar condition in cats known as feline immunodeficiency virus or FIV. You may also have heard of the medical term leukemia. Unlike the human form of leukemia, feline leukemia is a contagious virus that spreads from cat to cat. So, what exactly are these viruses and why are they so important?

Feline Immunodeficiency Virus (FIV)

Feline immunodeficiency virus or FIV is a retrovirus* that only infects cats and works by compromising the cat's immune system. This virus specifically targets white blood cells named T-helper cells. T-helper cells are responsible for activating other immune cells in the body by eliciting an immune response to fight infection. As the virus attacks, the cat is essentially left immunodeficient and becomes more susceptible to various infections.

Feline Leukemia Virus (FeLV)

Feline leukemia virus or FeLV is a retrovirus* that targets the immune system by attacking the bone marrow which produces immune cells. This virus differs from the leukemia that we may think of first because in humans, leukemia is primarily caused by cancer and not by a virus. Both forms of leukemia attack bone marrow and cause severe immunosuppression.

What’s the difference?

1. Transmission: FIV is transmitted through bite wounds from an infected cat while FeLV is transmitted through any close contact such as sharing litter boxes and mutual grooming.

2. Lifespan: FIV positive (FIV+) cats often live a full life while FeLV positive (FeLV+) cats can have a shortened lifespan.

3. Symptoms: FIV+ cats are often asymptomatic, but the most common symptom is recurrent infections due to a weakened immune system. FeLV+ cats can have a wide range of symptoms, and symptoms often worsen as the infection progresses. Some symptoms include loss of appetite, weight loss, enlarged lymph nodes, persistent fever, pale gums, persistent diarrhea, and seizures.

4. Vaccination: There is no vaccine currently available for FIV. There is a vaccine available for FeLV, which is offered at SVC!

Preventative care and treatment

Testing for both FeLV and FIV is recommended for all kittens at their first visit to SVC. For FeLV, the vaccine and limiting contact with outside cats is recommended for prevention. For FIV, there is no effective prevention outside of limiting contact with other cats of unknown FIV status. Treatment for both viruses comes in the form of symptom management as there is no cure for either disease. For FIV and FeLV, treatment consists of preventing secondary infections associated with the disease and working closely with us at SVC to manage your pet’s care.

Want to Schedule an Exam?

We have FeLV/FIV test in-house and can get your answers quickly! Schroeck Veterinary Care is open from Monday through Thursday for exams! Call us at (321)482-4838 to get scheduled! *A retrovirus is a virus that carries its own genetic material and incorporates its genetic material into that of its host. This means that the virus becomes part of the host’s genome.

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Resources:

• Feline Immunodeficiency Virus (FIV) | Cornell University College of Veterinary

• Medicine Feline Immunodeficiency Virus (FIV) - Cat Owners - Merck Veterinary Manual

• Feline Leukemia Virus (FeLV) - Cat Owners - Merck Veterinary Manual

• Feline Leukemia Virus | Cornell University College of Veterinary Medicine

• Feline Leukemia Virus (FeLV) - Veterinary Partner - VIN