Immunodeficiency in Cats (FIV — Feline Immunodeficiency Virus)

Overview

When people say a cat has "immunodeficiency," they're almost always referring to FIV (Feline Immunodeficiency Virus) — sometimes called "feline AIDS" because it's related to HIV in humans, though it behaves quite differently and has a much better long-term outlook than that comparison suggests.

• A lifelong retrovirus infection with no cure, but often a manageable, low-impact condition
• Different from FeLV (Feline Leukemia Virus) — a related but generally more aggressive virus; some cats are tested for both together
• Many FIV-positive cats live normal or near-normal lifespans, especially with good care
• Not transmissible to humans or other species — only cats

Common Symptoms

Important: many FIV-positive cats show NO symptoms for years, sometimes their entire lives.

When symptoms do appear (usually much later)

• Recurrent infections that are slow to resolve (skin, mouth, respiratory)
• Chronic gingivitis/stomatitis (see the Gingivitis article — FIV-positive cats are more prone to this)
• Weight loss over time
• Recurring fevers
• Increased susceptibility to secondary illnesses generally, since the immune system's ability to fight infection is gradually reduced

Possible Causes

• Transmitted primarily through deep bite wounds — meaning cat fights are the main transmission route
• Much more common in outdoor, unneutered male cats due to fighting behavior
• Rarely transmitted from mother to kittens
• Indoor, non-fighting cats are at very low risk of contracting FIV

Diagnosis

• Blood antibody test — commonly done as a quick in-clinic test, often combined with FeLV testing
• Kittens under 6 months can show false positives from maternal antibodies, so retesting later may be recommended
• Confirmatory testing (like Western blot or PCR) may be used if results are unclear or unexpected

Treatment

• No cure exists — management focuses on supporting the immune system and promptly treating any secondary infections
• Keeping FIV-positive cats indoors protects both them (from additional infections and fight-related re-injury) and other cats (from transmission)
• Routine veterinary checkups, typically more frequent than for uninfected cats, to catch secondary issues early
• Prompt, thorough treatment of any infection, even minor ones, since these cats may take longer to fight things off
• Some vets use immune-supportive therapies in individual cases, though no treatment reverses the underlying infection

Nutrition & Food Intake

• High-quality, complete nutrition supports overall immune function
• Avoid raw diets specifically for FIV-positive cats, since their reduced immune function makes them more vulnerable to foodborne bacterial or parasitic infections
• No special "FIV diet" exists, but consistent, high-quality nutrition matters more given their vulnerability to secondary illness

Home Physical Checks (What to Look For Yourself)

• Mouth/gums – FIV-positive cats are more prone to gingivitis/stomatitis; regular checks matter
• Weight – track for gradual, unexplained loss over time
• Skin and coat – watch for slow-healing wounds or recurring skin issues
• General demeanor – any new lethargy or recurring "off" periods worth mentioning at checkups
• Fever signs – warmth, lethargy, reduced appetite in cycles

Supportive Supplements (General Info — Not a Prescription)

• Omega-3 fatty acids – sometimes used for general immune and inflammatory support
• No supplement cures or significantly alters the course of FIV itself
• Focus remains on high-quality nutrition, indoor lifestyle, and prompt treatment of secondary issues rather than any specific supplement regimen

When to Seek Emergency Care

FIV itself is not typically an emergency, but seek prompt care for an FIV-positive cat if:

• Any infection seems to be progressing quickly or not responding to initial treatment
• Significant lethargy, fever, or appetite loss develops
• Any new, unexplained symptom — these cats benefit from a lower threshold for veterinary evaluation given their reduced immune resilience

Prevention

• Keep cats indoors to prevent fighting, the primary transmission route
• Spay/neuter reduces roaming and fighting behavior significantly
• Test new cats before introducing them to a household, especially rescues with unknown backgrounds or history of outdoor/fighting exposure
• No FIV vaccine is currently widely available/used in most regions — prevention relies on avoiding exposure

Prognosis

This is one of the more reassuring diagnoses on this list, despite its scary reputation:

• Multiple studies have found that FIV-positive status alone does not significantly shorten lifespan in cats with good care and a stable, single-cat or low-stress household
• One long-term monitoring study actually found a higher percentage of FIV-negative cats died during the study period than FIV-positive cats
• A comparative study found median survival for FIV-positive cats was substantially longer than for FeLV-positive cats (FIV alone: around 2,040 days vs. FeLV: around 714 days in one dataset) — FIV and FeLV are genuinely different in severity, and confusing them can cause unnecessary distress
• Many FIV+ cats today live 15 years or more
• Historically, more FIV-positive cats have lost their lives due to being harder to get adopted (and therefore more likely to be euthanized in shelters) than from the virus itself directly — a genuinely important fact for anyone in rescue work to know and share

Sources: Cat Chat FIV Monitoring Project (Glasgow Veterinary School); ScienceDirect comparative FIV/FeLV survival study; University of Illinois College of Veterinary Medicine; PMC clinical review of feline retroviruses.