Feline immunodeficiency virus
Also known as: FIV, Feline AIDS
In short
Feline Immunodeficiency Virus (FIV) is a common viral infection that slowly weakens a cat's immune system. While often compared to human HIV, FIV-positive cats can live long, comfortable lives with proper indoor husbandry, routine veterinary care, and prompt treatment of secondary infections.
TL;DR. Feline Immunodeficiency Virus (FIV) is a common viral infection that slowly weakens a cat's immune system, but with proper indoor care and prompt veterinary attention, infected cats can live long, comfortable lives.
With proper indoor management, many FIV-positive cats live comfortable, active lives.
Feline Immunodeficiency Virus (FIV) is a common infectious disease in cats caused by a lentivirus, a member of the same family of viruses as the human immunodeficiency virus (HIV). It is crucial to understand at the outset that FIV is strictly species-specific; it cannot be transmitted to humans or other non-feline pets. The virus operates by targeting and slowly destroying CD4+ T-lymphocytes, which are specialized white blood cells essential for coordinating the body's immune response. Over time, this progressive destruction leads to a decline in cell-mediated immunity.
As the immune system's defense network degrades, the cat enters a chronic state of immunodeficiency. This stage is clinically similar to human acquired immunodeficiency syndrome (AIDS). Because the body can no longer defend itself effectively, the cat becomes highly susceptible to opportunistic infections—illnesses caused by common environmental bacteria, fungi, or protozoa that a healthy immune system would easily fight off. Additionally, FIV-positive cats are at a significantly higher risk for chronic inflammatory conditions and lymphoid malignancies, such as lymphoma.
Understanding FIV is vital for every cat owner because the infection is lifelong. However, a diagnosis is no longer considered an immediate death sentence. Many cats co-exist with the virus for years without showing severe clinical signs, provided they receive attentive husbandry and targeted veterinary care.
The primary transmission route of FIV is through direct, blood-borne contact, most commonly via deep bite wounds. Saliva from an infected cat contains high concentrations of the virus, and when injected into the tissue of another cat during a fight, transmission readily occurs. Because of this, certain demographics are highly overrepresented.
"Aggressive biting behavior is thought to be the primary route of transmission of FIV; older, male, outdoor cats with clinical signs of disease are most commonly infected. The prevalence of FIV antibodies in North America was 2. 5% in a recent study (Levy et al, 2006)."
Intact, outdoor male cats are at the highest risk due to territorial roaming and fighting behaviors. While casual contact—such as sharing water bowls, grooming, or sleeping together—carries a very low risk of transmission, it is not entirely impossible in highly unstable social groups where minor scuffles occur.
Other, less common routes of transmission exist. The virus is present in semen and can be transmitted via artificial insemination or natural mating. Furthermore, transplacental and perinatal transmission from an infected mother queen to her kittens can occur, particularly if the queen contracts the virus during pregnancy when her viral load is exceptionally high. There are no known breed predispositions to FIV; any cat, regardless of breed, can contract the virus if exposed to an infected individual.
The clinical presentation of FIV is highly variable and depends on the stage of the disease. After initial infection, cats may experience a transient fever and swollen lymph nodes, which often go unnoticed. They then enter a prolonged subclinical latent phase that can last for years. Eventually, as immunodeficiency develops, clinical signs emerge.
Anterior uveitis is an occasional ocular complication seen in cats with FIV.
Diagnosing FIV requires a systematic approach, starting with screening tests and moving to confirmatory diagnostics if necessary. Because the virus is slow-acting, identifying it early allows for proactive management.
The gold standard for initial screening is the FIV antibody test, typically performed in the clinic using an enzyme-linked immunosorbent assay (ELISA) or lateral flow kit. Unlike many other viral tests that look for the virus itself (antigens), this test detects the antibodies the cat's immune system has produced in response to the virus. Because FIV causes a permanent, lifelong infection, the presence of antibodies indicates that the cat is infected. However, this test has a major caveat: kittens under six months of age may test positive due to antibodies received from an infected mother's milk (maternal antibodies), and vaccinated cats will also test positive because the vaccine stimulates antibody production.
To resolve ambiguous results, your vet may recommend an FIV RT-PCR assay. This test looks for the actual genetic material of the virus. However, PCR testing has its own limitations:
"The biggest problem with FIV RT-PCR assays to date is lack of standardization among laboratories and the potential for both false-positive and false-negative results (Crawford et al, 2005)."
Consequently, PCR results must always be interpreted in conjunction with the cat's clinical history and antibody status.
Additional diagnostic workups are essential to evaluate the cat's overall health and identify secondary complications. Your vet will likely recommend:
If an FIV-positive cat is showing signs of illness, your vet will perform a comprehensive workup to rule out other concurrent infections, as treating these secondary issues is the key to maintaining quality of life.
In-clinic antibody tests are the primary screening tool for diagnosing FIV.
There is no cure for FIV, so treatment focuses on suppressing viral replication, modulating the immune response, and aggressively managing secondary infections. Therapies are categorized by their line of intervention and mechanism of action.
"interferon-α led to improved clinical signs and prolonged survival compared with a placebo-treated control group in one study (Pedretti et al, 2006). In another study feline recombinant interferon was administered at 106 U/kg/day"
Beyond these specific therapies, aggressive supportive care is paramount. Cats with severe stomatitis often require broad-spectrum antibiotics, pain management, and sometimes full-mouth dental extractions to eliminate oral inflammation. Secondary bacterial infections must be diagnosed promptly via culture and sensitivity testing and treated with longer-than-normal courses of antibiotics.
The prognosis for an FIV-positive cat is highly variable and not universally poor. The subclinical latent period can last for several years, during which the cat can enjoy an excellent quality of life with no outward signs of illness. A positive antibody test alone is never a reason for euthanasia.
Once a cat transitions into the immunodeficiency stage, the prognosis becomes heavily dependent on how well concurrent opportunistic infections or secondary conditions respond to treatment. If secondary diseases, such as lymphoma or severe bone marrow suppression, develop, the prognosis becomes more guarded. However, with diligent indoor housing, high-quality nutrition, and rapid veterinary intervention at the first sign of illness, many FIV-positive cats live normal lifespans.
Preventing FIV relies primarily on minimizing exposure to infected cats. Because aggressive biting is the primary transmission route, the most effective preventative measure is keeping your cat strictly indoors. This eliminates the risk of territorial fights with outdoor cats of unknown infection status.
For households with multiple cats, ensuring a stable, non-aggressive social structure is key. If a new cat is introduced, they should be isolated and tested for FIV antibodies before being allowed to interact with resident cats. Spaying and neutering are also highly effective preventative tools, as they dramatically reduce roaming and aggressive behaviors in male cats.
A vaccine against FIV has been licensed in the United States. However, its use is controversial and requires careful discussion with your veterinarian:
"This vaccine induces antibodies that cannot be distinguished from those induced by naturally occurring disease with currently available tests."
If a vaccinated cat is ever lost or tested at a shelter, they will test positive on standard antibody screening tests, which can lead to diagnostic confusion.
Because FIV-positive cats have compromised immune systems, minor symptoms can rapidly escalate into life-threatening emergencies. You should contact your veterinarian if you notice:
Seek immediate emergency veterinary care if your cat exhibits:
Treatment must be prescribed by a licensed veterinarian based on your pet. Specific drug doses are intentionally not shown here.
Feline Immunodeficiency Virus (FIV) is a common viral infection that slowly weakens a cat's immune system. While often compared to human HIV, FIV-positive cats can live long, comfortable lives with proper indoor husbandry, routine veterinary care, and prompt treatment of secondary infections.
Anorexia、Depression、Fever、Generalized lymphadenopathy、Nonregenerative anemia、Stomatitis、Thrombocytopenia、Weight loss
FIV antibody test、Bone marrow aspirate cytology、CD4+/CD8+ ratio evaluation、Complete Blood Count (CBC)、FIV RT-PCR assay
Treatment must be prescribed by a licensed veterinarian based on your pet. Specific drug doses are intentionally not shown here.
This article is for general education and is not a substitute for professional veterinary advice. If your pet is unwell, please consult a veterinarian.
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