Few test results frighten cat owners more than a positive line for FIV or FeLV. The names alone, feline immunodeficiency virus and feline leukemia virus, sound like a death sentence, and for decades they were treated as one. They are not the same virus, they do not behave the same way, and a positive result means very different things depending on which one you are looking at. Some infected cats live well into old age. Understanding the difference is the first step toward making good decisions.
Two Viruses, Two Very Different Stories
Both are retroviruses, meaning they insert genetic material into the cat’s own cells, and both suppress the immune system over time. Beyond that they diverge sharply.
| Feature | FIV | FeLV |
|---|---|---|
| Primary spread | Deep bite wounds, mostly between unneutered outdoor males | Close friendly contact: mutual grooming, shared bowls, mother to kitten |
| Typical course | Slow; many cats stay healthy for years | More variable; roughly half of infected cats develop regressive infection and fare well |
| Household risk to other cats | Very low among stable, neutered cats | Real, especially for kittens and unvaccinated cats |
| Vaccine | Available in some countries, not widely used | Widely available; test before vaccinating |
The practical takeaway is that an FIV-positive cat and an FIV-negative cat can often share a home with minimal risk, provided both are neutered and nobody is fighting. FeLV needs more careful management.
How Each Virus Spreads
- FIV is transmitted mainly through bite wounds, which is why free-roaming, unneutered males are overrepresented. Casual contact, shared litter boxes, and shared food bowls are not significant routes.
- FeLV spreads through saliva during mutual grooming, from shared food and water bowls, and from an infected mother to her kittens. Deep bites also transmit it.
- Neither virus survives long in the environment. They are fragile and are readily killed by ordinary disinfectants, so contaminated surfaces and cat shows are not meaningful sources of infection.
Testing: Why One Test Is Often Not Enough
The standard first test is a point-of-care test run in the clinic. It detects FIV antibodies and FeLV antigen. A positive result on that test is meaningful but not always final. FeLV in particular produces several outcomes: abortive, where the cat clears the virus; regressive, where the infection is suppressed but not eliminated; and progressive, where it is not controlled. Regressive cats typically test positive on whole blood, negative on serum, and have low provirus levels, and they usually have normal survival times. Confirmatory testing, often a quantitative PCR, helps separate these. Testing also needs repeating when exposure was recent, since a cat infected days ago may still test negative. Standard guidance is to test again at least thirty days after the last known risk.
Living Well With a Positive Cat
Management of infected cats rests on preventive care done consistently rather than on antiviral drugs, for which the evidence remains thin. That means regular physical examinations, routine laboratory monitoring, core vaccinations, parasite control, dental care, and prompt attention to any illness, because a suppressed immune system turns minor problems into major ones. Keep your cat indoors, both to reduce exposure to other pathogens and to prevent spreading the virus. Feed a complete diet, keep body condition healthy, and avoid raw meat and raw eggs, which carry infection risk that an immunocompromised cat handles poorly.
Protecting the Rest of the Household
Have every cat in the home tested, and retest any cat with known exposure after thirty days. Vaccinate uninfected cats against FeLV if they have any risk of exposure, and test before vaccinating so a positive result is not masked or misread. Neutering removes the fighting and roaming behavior that drives FIV transmission, which is one of the most effective interventions available. If a new cat is joining the household, isolate it until testing is complete.
A positive retrovirus test is the beginning of a care plan, not the end of one. Ask which virus, ask what the confirmatory test showed, and ask what monitoring schedule your veterinarian recommends. Many of these cats spend years doing what cats do best: sleeping in the sun and supervising their humans.