Understanding Feline Leukemia Virus (FeLV) in Cats
Feline leukemia virus (FeLV) stands out as one of the most significant infectious diseases affecting cats globally. This retrovirus primarily targets domestic cats but can also infect certain wild feline species. Unlike some other viruses, FeLV is not a threat to dogs or humans—it's strictly a feline concern.
How FeLV Spreads Among Cats
The main route of FeLV transmission is through infected saliva during close contact. This includes mutual grooming, sharing food and water bowls, litter boxes, and bite wounds. The virus can also be present in urine, feces, blood, nasal secretions, and milk. Mother cats may pass FeLV to their kittens either before birth or while nursing. Rarely, transmission occurs via contaminated instruments or blood transfusions.
Fortunately, FeLV doesn't survive long outside a cat's body—usually less than a few hours under normal conditions—and common disinfectants easily inactivate it. So environmental contamination poses much less risk than direct cat-to-cat contact.
Cats Most at Risk
Certain groups are more vulnerable to FeLV infection:
- Cats with prolonged exposure to infected felines (such as outdoor cats or those in multicat households)
- Kittens and young cats (their immune systems aren't fully developed)
- Kittens born to infected mothers
Adult cats may develop some resistance over time, but even healthy-appearing infected cats can shed the virus and remain contagious.
What Happens After Exposure?
The outcome after exposure to FeLV varies depending on the cat's immune response. There are several possible scenarios:
- Abortive infections: The immune system eliminates the virus before it takes hold. These cats test negative for FeLV antigens and don't spread the disease.
- Regressive infections: The virus becomes dormant (often in bone marrow), with no viral particles circulating in the blood. These cats are typically non-contagious unless their immune system becomes compromised later on.
- Latent infections: The virus persists at low levels in certain cells; it's usually only detectable by sensitive PCR tests and isn't generally contagious unless reactivated.
- Progressive infections: The immune system fails to contain the virus, leading to ongoing replication. These cats actively shed the virus and often become ill.
Disease Effects: What Does FeLV Do?
FeLV can wreak havoc on a cat's body in multiple ways:
- Cancer: Especially lymphoma and leukemia
- Blood disorders: Such as anemia
- Immune suppression: Increased vulnerability to other infections
- Mouth inflammation: Stomatitis or gingivitis
- Nervous system issues:
- Diverse organ involvement:
The signs of illness vary widely—sometimes progressing over weeks, months, or even years—and may include loss of appetite, weight loss, poor coat condition, pale or yellow gums (anemia or jaundice), swollen lymph nodes, fever, chronic infections (skin, bladder, respiratory tract), persistent diarrhea or vomiting, lethargy, oral disease, reproductive problems (like abortions), and neurologic changes such as seizures or behavioral shifts.
Diagnosing Feline Leukemia Virus
The most common diagnostic tool is a blood test called ELISA that detects viral proteins in blood, saliva, or tears. Because some cats clear the infection naturally, retesting after several weeks is recommended if an initial test comes back positive. An IFA test helps confirm persistent infection by detecting the virus inside white blood cells. PCR tests can spot FeLV DNA when the virus isn't circulating freely.
Lifespan and Prognosis for Infected Cats
A positive test doesn't always mean a cat will stay sick forever—many clear the infection and live normal lives without spreading the disease further. However, about 85% of persistently infected cats die within three to four years of diagnosis; median survival time hovers around 2.4 to 2.5 years after diagnosis for those who don't clear it. Some with regressive infection remain healthy for many years.
Treatment Options: Managing Life with FeLV
No cure exists for FeLV yet; treatment focuses on managing symptoms and secondary infections. Supportive care might include antibiotics for bacterial infections, anti-inflammatory drugs for comfort, appetite stimulants if eating drops off, blood transfusions for severe anemia cases, or chemotherapy for cancers related to FeLV.
Regular veterinary check-ups every 6–12 months are crucial. Quick action at any sign of illness helps keep affected cats comfortable longer. Infected felines should stay indoors—not just for their own health but also to prevent spreading FeLV to others.
Prevention: Keeping Cats Safe from FeLV
- Routine testing: Especially before introducing new cats into a household
- No sharing of food bowls/litter boxes between infected and uninfected animals
- Kittens should be vaccinated as part of core vaccinations;
- Cats with outdoor access or high risk should receive vaccines too;
- No vaccine is perfect—so minimizing exposure remains key even after vaccination;
Cats won't test positive on standard antigen tests just because they've been vaccinated—so you don't need to worry about false positives from routine shots.
When Should You Test Your Cat?
- Kittens at their first vet visit
- Cats joining new households with uninfected residents
- Cats prior to receiving an FeLV vaccine
- Cats exposed to others whose status is unknown
If your cat does test positive for FeLV: focus on good nutrition; provide a low-stress environment; schedule regular veterinary visits; minimize sources of infection; act quickly if any new symptoms appear; keep them indoors so they don't catch other illnesses—or pass along this one.
Early detection plus responsible management help reduce suffering while protecting both your pet and other members of your feline family.
