Feline Immunodeficiency Virus (FIV) is a viral infection that weakens a cat's immune system, making affected cats more susceptible to secondary infections, certain cancers, and other health complications. FIV is a lentivirus, similar in structure to Human Immunodeficiency Virus (HIV), and in advanced stages it can lead to a condition comparable to acquired immunodeficiency syndrome (AIDS) in humans. Because of these similarities, FIV is sometimes informally referred to as "cat HIV" or "feline AIDS," although it is a species-specific virus and cannot infect humans.
Although FIV is a serious diagnosis, it is not as common as many people assume. Studies from veterinary hospitals in the United States and Canada estimate that approximately 3–4% of cats test positive for FIV. Importantly, many FIV-positive cats live long, comfortable lives with proper care. The virus itself is not immediately life-threatening to an otherwise healthy cat, but long-term immune suppression can increase health risks over time.
Modes of Transmission
FIV is transmitted primarily through deep bite wounds. Infected cats carry high concentrations of the virus in their saliva, and bites allow the virus to enter the bloodstream. As a result, unneutered male cats that roam outdoors and engage in territorial fighting are at the highest risk.
Transmission through casual contact — such as mutual grooming, sharing food and water bowls, or using the same litter box — is considered very unlikely. While the virus is present in saliva, it does not spread easily without direct access to the bloodstream. Sexual transmission is possible but is far less common than transmission through bite wounds.
Common Signs and Symptoms: Acute Infection vs. Chronic Disease
Acute (Initial) Phase
During the early phase of infection, some cats may show mild, nonspecific symptoms such as:
- Fever
- Lethargy
- Enlarged lymph nodes
Many cats show no noticeable symptoms at all during this stage.
Asymptomatic (Latent) Phase
After the initial phase, cats often enter a prolonged period — lasting months or even years — during which they appear completely healthy. Despite the lack of outward signs, the virus continues to slowly weaken the immune system.
Advanced Disease (Immunodeficiency Stage)
Once immune function declines significantly, cats may develop secondary infections, autoimmune disorders, or cancers such as lymphoma. Symptoms may include:
- Weight loss
- Poor appetite
- Dull or unkempt coat
- Chronic lethargy
- Redness, inflammation, or sores in the mouth
- Eye inflammation
- Difficulty breathing
- Vomiting or diarrhea
- Chronic coughing or sneezing
- Neurologic signs such as seizures or behavioral changes
Not all FIV-positive cats progress to this stage.
Diagnosis
FIV is most commonly diagnosed using an enzyme-linked immunosorbent assay (ELISA) blood test, which detects antibodies to the virus. This test is widely used in veterinary medicine and is also commonly paired with testing for Feline Leukemia Virus (FeLV).
While ELISA tests are generally reliable, false positives can occur. Confirmatory testing may be recommended in certain situations, including:
- Recent exposure (before antibodies have formed)
- Testing kittens under six months of age
- Unexpected positive results in low-risk cats
It typically takes 2–4 months after infection for a cat to develop detectable antibodies. Additionally, kittens may test positive due to maternal antibodies passed from an infected mother, even if they are not truly infected, making early testing unreliable.
Treatment: Management Without a Cure
There is currently no cure for FIV. Once infected, a cat will carry the virus for life. Treatment focuses on supporting immune health and promptly addressing secondary illnesses.
General management recommendations for FIV-positive cats include:
- Keeping cats indoors to reduce exposure to infectious agents and prevent transmission to other cats
- Providing excellent nutrition and avoiding raw diets
- Seeking prompt veterinary care for any signs of illness
- Scheduling regular veterinary exams every 4–6 months to detect problems early
In some cases, antiviral medications such as zidovudine (AZT) may be used to help manage certain symptoms, but these drugs can have significant side effects and are not appropriate for every cat.
Final Thoughts
With proper care and regular veterinary monitoring, many cats with FIV live long, fulfilling lives. Some may never progress to advanced immunodeficiency, while others may experience a more rapid decline once severe immune suppression develops. When progression occurs, deterioration can be swift, and prognosis becomes guarded.
Prevention remains the most effective strategy against FIV. Keeping cats indoors and preventing fights with other cats significantly reduces the risk of infection. Cats diagnosed with FIV should be kept indoors and not allowed to roam freely, both for their own health and to protect other cats.