Feline immunodeficiency virus (FIV) is a viral infection that weakens a cat’s immune system over time, making it harder for the body to fight off everyday illnesses. It’s often compared to HIV in humans because both viruses work in similar ways, but FIV only infects cats and poses zero risk to people or other animals. Despite its serious-sounding name, many FIV-positive cats live long, comfortable lives with basic care.
How FIV Attacks the Immune System
FIV belongs to a family of viruses called lentiviruses, meaning it works slowly. Once inside a cat’s body, it targets immune cells called T-lymphocytes, which are the white blood cells responsible for coordinating the immune response. The virus infects both the “helper” cells (CD4+) that direct immune attacks and the “killer” cells (CD8+) that destroy infected cells directly.
Over months and years, FIV gradually flips the normal ratio of these two cell types. A healthy cat has more helper cells than killer cells, but FIV inverts that balance. As helper cell numbers drop, the immune system becomes less organized and less capable of responding to new threats. This is why FIV-positive cats don’t typically die from the virus itself. Instead, they become vulnerable to infections and illnesses that a healthy immune system would normally handle without trouble.
Interestingly, a cat’s killer cells do fight back. Research has shown that these CD8+ cells can produce substances that suppress FIV replication without destroying the infected cells. This built-in defense mechanism is part of why FIV progresses so slowly and why many cats remain healthy for years after infection.
How Cats Get FIV
The primary route of transmission is bite wounds. When an infected cat bites deeply enough to break the skin, the virus in its saliva enters the other cat’s bloodstream. This makes unneutered male cats with outdoor access the highest-risk group, since they’re the most likely to get into territorial fights.
Casual contact does not spread FIV efficiently. Sharing water bowls, food dishes, litter boxes, and mutual grooming are not meaningful transmission routes. Cats in households with stable social structures, where housemates don’t fight, are at very little risk of spreading the virus between them. This is an important point for anyone considering adopting an FIV-positive cat into a multi-cat home.
Mother-to-kitten transmission happens only on rare occasions. Sexual contact is also not a significant way FIV spreads. The virus is really a disease of aggression, not affection.
FIV Cannot Infect Humans
There is no evidence that any person has ever been infected with FIV. Studies have specifically looked at people with close exposure to FIV-positive cats, including those who were bitten by infected cats or accidentally injected with the virus in laboratory settings. No infections were found. FIV is strictly limited to cats.
Stages of Infection
FIV progresses through three general phases. The first is an acute phase that occurs a few weeks after infection. During this stage, a cat may develop a mild fever, swollen lymph nodes, or brief lethargy as the virus establishes itself and the immune system mounts its initial response. Many owners never notice these signs because they’re subtle and resolve on their own.
The second phase is a long, clinically silent period where the cat appears completely healthy. This asymptomatic stage can last for years, sometimes the majority of the cat’s life. The virus is still present and slowly affecting the immune system, but outward signs of illness are absent.
The third phase occurs when immune suppression becomes severe enough that the cat starts developing chronic or recurring illnesses. These can include persistent mouth and gum inflammation, respiratory infections, skin infections, digestive problems, and eye inflammation. Weight loss, poor coat condition, and ongoing fevers are also common in this later stage. Not every FIV-positive cat reaches this point, and how quickly the disease progresses varies widely between individual cats.
How FIV Is Diagnosed
Most veterinary clinics screen for FIV using a rapid blood test (a type of ELISA) that detects antibodies the cat’s immune system has produced against the virus. These screening tests are quite accurate, with sensitivity around 89 to 97 percent and specificity around 95 to 97 percent.
However, there’s an important complication. Cats that were vaccinated against FIV (a vaccine that was available for some years) produce antibodies that look identical to those from a natural infection. The standard screening test cannot tell the difference. For cats whose vaccination history is unknown, PCR testing, which looks for the virus’s genetic material rather than antibodies, can help clarify the picture. PCR tests have a sensitivity of about 85 to 92 percent and specificity up to 99 percent.
Kittens born to FIV-positive mothers can also test positive on antibody tests because they carry their mother’s antibodies for the first several months of life. Retesting after six months of age gives a more reliable result in these cases.
How Long FIV-Positive Cats Live
This is often the first question owners ask, and the answer is more reassuring than most people expect. A study of owned pet cats at a referral clinic found that FIV-positive status did not significantly affect longevity compared to cats without any retrovirus. The median survival time for FIV-positive cats in that study was about 5.6 years from the point they entered the study, compared to roughly 10.8 years for uninfected cats. But the key finding was that the difference was not statistically significant for FIV alone.
By contrast, cats positive for feline leukemia virus (FeLV) had dramatically shorter survival times, about 2 years, and cats with both FIV and FeLV had a median survival of just 77 days. FIV on its own is a far more manageable diagnosis than FeLV.
Many FIV-positive cats live well into their teens with appropriate care. The diagnosis is not a death sentence, and it shouldn’t be a reason to euthanize an otherwise healthy cat or pass one over for adoption.
Caring for an FIV-Positive Cat
The cornerstone of managing FIV is keeping the cat’s immune system as strong as possible and minimizing exposure to new infections. European veterinary guidelines recommend health checks at least every six months, including weight monitoring and periodic blood work and urinalysis to catch problems early.
Keeping an FIV-positive cat indoors serves two purposes: it protects the cat from encountering new pathogens and prevents transmission to other cats through fighting. Neutering is recommended for all FIV-positive cats, since it reduces aggression, roaming behavior, and the urge to fight.
When FIV-positive cats need surgery or dental work, veterinarians typically use antibiotics as a precaution because the compromised immune system may be slower to prevent surgical site infections. Routine dental care is especially important since mouth and gum inflammation is one of the most common problems FIV-positive cats face.
A nutritionally complete diet, consistent parasite prevention, and a low-stress home environment round out the basics. FIV-positive cats don’t need exotic treatments or constant medical intervention. They need the same good care any cat deserves, just with a bit more vigilance and slightly more frequent vet visits.
Living With Other Cats
Because FIV spreads through bite wounds rather than casual contact, an FIV-positive cat can live safely with uninfected cats in a household where the cats get along. The critical factor is the social dynamic. If the cats groom each other, share space peacefully, and don’t fight, the risk of transmission is very low.
Shelter guidelines recommend housing FIV-positive cats separately from negative cats as a precaution, especially since shelter environments can be stressful and unfamiliar cats are more likely to fight. But in a stable home where introductions are done properly, mixed-status households work well for many families.