Author: Carol Campbell, DVM
Medical Director, Valley Humane Society
When a cat is diagnosed with a viral infection such as Feline Immunodeficiency Virus (FIV) or Feline Leukemia Virus (FeLV), it can feel overwhelming at first. These diagnoses often come with fear and uncertainty, but the reality is more nuanced—and often more hopeful—than many people expect. With good care and the right information, many of these cats go on to live comfortable, meaningful lives.
What is FIV?
FIV is a virus that affects a cat’s immune system, somewhat similar to Human Immunodeficiency Virus (HIV) in humans. However, FIV is strictly a feline disease and cannot be transmitted to people or other species. The virus is most commonly spread through deep bite wounds, which is why it tends to be seen more often in unneutered male cats that are prone to fighting. It can also be transmitted through mating behavior.
FIV is a lifelong infection, but not necessarily a life-limiting one. Many FIV-positive cats remain healthy for years—sometimes for their entire lives—without ever developing serious complications. Over time, the virus can weaken the immune system, making affected cats more vulnerable to secondary infections. Because of this, early detection and prompt treatment of even minor illnesses are important.
What to know about testing for FIV
Testing for FIV is straightforward and involves a simple blood test. However, timing matters. Kittens younger than five months may test falsely positive due to maternal antibodies, which can be a confusing and stressful result to receive. Likewise, after a potential exposure such as a bite, it can take up to two months before the virus is detectable in the bloodstream. While a vaccine for FIV does exist, it is not fully protective and can interfere with future testing, so it is not commonly recommended for low-risk, indoor cats.
Because testing is not recommended as part of standard intake at animal shelters, Valley Humane Society uses FIV testing as a diagnostic tool, utilized when a cat demonstrates FIV symptoms or shows signs of potential exposure.
How to handle FIV in your home
Living with an FIV-positive cat is often much easier than people expect. Because the virus is primarily spread through biting, cats that coexist peacefully without fighting are at an extremely low risk of transmission. In many cases, FIV-positive and negative cats can live together safely in a stable, non-aggressive household. Keeping FIV-positive cats indoors is strongly recommended, both to protect them from infections and to prevent potential spread.
What is FeLV?
An FeLV diagnosis presents a different set of challenges. This virus is more easily transmitted than FIV and is commonly spread through close social contact, such as grooming or sharing food and water bowls. It can also be passed from a mother cat to her kittens, through mating, or via blood exposure during fights. Like FIV, FeLV is not contagious to humans or other species.
What makes FeLV particularly complex is the range of ways a cat’s body can respond to the infection. Some cats are able to eliminate the virus entirely and develop immunity. Others may suppress it to low levels, while some develop a persistent infection that affects the bone marrow and immune system. These different responses—often described as abortive, regressive, or progressive infections—mean that prognosis can vary widely from one cat to another.
Cats with persistent FeLV infection may appear completely healthy for months or even years. However, over time, the virus can lead to immune suppression, leaving them more susceptible to infections. It is also associated with serious conditions such as anemia and certain cancers, including lymphoma and leukemia. Although there is no cure for persistent FeLV infection, supportive care and regular veterinary monitoring can significantly improve both quality and length of life.
What to know about testing for FeLV
Testing for FeLV is somewhat more complicated than for FIV. Different types of tests are available, and results may occasionally conflict, making interpretation potentially more challenging. As with FIV, timing is important — testing too soon after exposure may not yield accurate results, as it can take up to a month for the virus to become detectable. An FeLV vaccine also exists, which does not interfere with testing and may be recommended under certain circumstances.
How to handle FeLV in your home
For cats living with FeLV, an indoor lifestyle is especially important. Because the virus spreads easily through close contact, FeLV-positive cats are best housed with other FeLV-positive cats or kept as single-cat households. Minimizing stress, maintaining good nutrition, and staying on top of routine veterinary care all play a crucial role in keeping these cats as healthy as possible.
A diagnosis of FIV or FeLV is not the end of a cat’s story
An FeLV/FIV test result represents just a single moment in time. A negative result does not always rule out very recent exposure, and a positive result does not always predict immediate illness. In fact, with relatively low infection rates in many cat populations—typically around 2 to 4 percent—most animal shelters, including Valley Humane, have moved away from routine testing in healthy, low-risk cats.
With clear communication with your veterinarian, along with attentive care, a secure environment, and regular monitoring, cats with these conditions can live full, happy lives.