Feline Immunodeficiency Virus (FIV) infection

Overview

FIV is a retrovirus (in the same family as human HIV, though it does not infect humans) that gradually weakens a cat's immune system over years. Many FIV-positive cats live long, largely normal lives with good care — this is a fundamentally different disease trajectory than the outdated 'feline AIDS' framing sometimes still suggests, and a positive test is not itself a reason for alarm or euthanasia.

Symptoms

• Often asymptomatic for years (mild, common)
• Recurrent or severe secondary infections (advanced disease) (moderate, uncommon)
• Weight loss (advanced disease) (moderate, uncommon)
• Chronic dental disease (mild, common)

Causes

Infection with feline immunodeficiency virus.

Risk Factors

Outdoor, unneutered male cats are at the highest risk, since the primary transmission route is deep bite wounds from fighting — this gives FIV a very different risk profile than FeLV, which spreads more through casual close contact.

Transmission

Primarily through deep bite wounds during fighting; much less commonly through other routes (mother-to-kitten transmission is possible but less common than with FeLV). FIV is transmitted primarily through deep bite wounds, making outdoor, unneutered male cats with a history of fighting the highest-risk population by a significant margin; it is NOT typically transmitted through casual contact like shared food bowls, mutual grooming, or simply living in the same household, which is an important, often-misunderstood distinction — FIV-positive and FIV-negative cats can often safely share a home if they aren't fighting.

Incubation Period

The period between infection and any noticeable illness can be years — this is a slowly progressive disease, not an acute one.

Disease Stages & Progression

An initial mild, often unnoticed phase, followed by a long asymptomatic (clinically silent) period that can last many years, eventually progressing in some cats to a phase of increased susceptibility to secondary infections and, less commonly, certain cancers, as the immune system gradually weakens. FIV progresses through a variable, sometimes very long asymptomatic period (many FIV-positive cats live for years with no apparent illness, particularly with a stable indoor environment and good general care) before eventually progressing, in some cats, to a stage where the weakened immune system allows secondary infections and illnesses to become more frequent or severe — this timeline varies enormously between individual cats and is genuinely not a predictable, fixed disease course the way some other viral infections are.

Early Warning Signs

Often none for years; when signs eventually appear they're usually related to a secondary infection (dental disease, skin infection, upper respiratory infection) that's more severe or recurrent than expected, rather than a specific 'FIV symptom.'

Advanced Symptoms

In advanced immune suppression: chronic or recurrent infections (dental, skin, respiratory, GI), weight loss, and increased susceptibility to certain cancers and secondary illnesses.

Diagnostic Methods

In-clinic antibody test; confirmatory testing (e.g., PCR or Western blot at a reference lab) for ambiguous or high-stakes results. A blood test (ELISA) is the standard initial screen, widely available as a same-day in-clinic test; because this test can occasionally give a false positive (particularly in kittens who may show maternal antibodies without being truly infected) or a false negative in very recently infected cats, a confirmatory Western blot or PCR test is recommended for a positive result specifically, particularly in a kitten or in a cat with no known exposure risk.

Veterinary Examination Process

General physical exam, with particular attention to dental health, skin, and any sign of chronic or recurrent infection, alongside routine testing.

Recommended Lab Tests

FIV antibody test, complete blood count, and additional testing directed at any specific secondary complication.

Diagnostic Imaging

Not used for diagnosis; used as needed to investigate a specific secondary complication.

Blood Test Indicators

An in-clinic antibody test (often run alongside the FeLV test) is the standard screen; results can occasionally be ambiguous in very young kittens (maternal antibodies) or need confirmatory testing.

Biopsy / Histopathology

Not applicable for FIV diagnosis itself; used if a suspected secondary cancer needs characterization.

Differential Diagnoses

Other causes of recurrent or unusually severe infections in an older cat; FIV testing is straightforward and typically done as part of a standard retrovirus screen alongside FeLV.

Home Monitoring Guidance

Regular attention to appetite, weight, and any new or recurrent infection, with prompt vet visits for anything that seems to be lingering longer or hitting harder than expected.

Veterinary Treatment Options

There is no cure or antiviral treatment that clears FIV, but there is also no specific treatment needed for the virus itself in an otherwise healthy-seeming cat — management focuses on routine excellent care, prompt and thorough treatment of any secondary infection, and regular monitoring. There is no cure for FIV, but there is also no specific antiviral treatment routinely used the way there might be for some other viral infections — management instead focuses on minimizing exposure to additional infections (keeping an FIV-positive cat indoors specifically reduces exposure to other pathogens their weakened immune system would struggle with more), prompt treatment of any secondary infections that do occur, and routine wellness care to catch problems early.

Surgery Requirements

Not applicable to FIV itself.

Recovery Timeline

Not applicable — this is a lifelong infection; the goal is stable long-term management, not recovery.

Possible Complications

Gradually increased susceptibility to infections and certain cancers over years, particularly once advanced immune suppression develops (which many FIV-positive cats never reach, or reach only very late in life).

Long-Term Management

Indoor-only living (both to protect the FIV-positive cat from additional infections and to prevent spread to other cats via fighting), twice-yearly veterinary checkups, excellent dental and preventive care, and prompt treatment of any infection.

Prevention

Neutering (reduces fighting-related risk significantly), keeping cats indoors or supervised to reduce fighting exposure, and testing new cats before introducing them to a multi-cat household.

Vaccination Availability

An FIV vaccine has existed in some markets historically but is not widely available or routinely recommended in many current guidelines, partly because it can complicate future antibody testing (vaccinated cats may test positive on standard antibody tests); discuss current availability and recommendations with your vet if relevant to your region.

Prognosis

Good for many cats — often a normal or near-normal lifespan, particularly with attentive care, indoor living, and routine veterinary attention. With attentive care — indoor living, a good diet, routine veterinary checkups, and prompt treatment of any illness — many FIV-positive cats live a normal or near-normal lifespan, and FIV status alone is not considered a reason to withhold adoption or make different lifestyle decisions than for any other cat, contrary to how this diagnosis was sometimes treated in the past.

References

American Association of Feline Practitioners (AAFP) Retrovirus Testing and Management Guidelines; WSAVA.

Medications Used

• Antibiotics or other treatment as needed for specific secondary infections — no FIV-specific medication exists in routine use

Estimated Treatment Cost by Country

Frequently Asked Questions