Serious severity
Feline Leukemia Virus (FeLV)
A retrovirus that gradually weakens the immune system. One of the most significant infectious causes of illness and death in domestic cats — but entirely preventable.
⚠️ Common symptoms
Feline leukemia virus is a retrovirus — a virus that splices its own genetic code into the DNA of the cells it infects. Despite its name it is not primarily a cancer, although it dramatically raises the risk of certain cancers; its central effect is the slow, progressive destruction of the immune system, which is why FeLV-positive cats so often fall ill with infections that a healthy cat would shrug off.
When a cat is first exposed, one of several things can happen. Some cats mount a successful immune response and clear the virus entirely. Others become 'regressively' infected — the virus goes dormant in the bone marrow, causing no illness but potentially reactivating years later under stress. The most serious outcome is a 'progressive' infection, in which the virus replicates continuously, is shed in saliva, and steadily undermines the cat's health. Age matters enormously here: kittens are highly vulnerable, while many healthy adult cats can fight the virus off.
Because FeLV is transmitted mainly through prolonged, friendly contact — shared bowls, grooming, and a mother nursing her kittens — it spreads most readily between cats that live together and like each other, rather than through brief encounters. This is why testing and separating cats of unknown status is so important in multi-cat homes, shelters, and rescues.
There is no cure, but a diagnosis is not the death sentence it once was. With indoor living, a high-quality diet, rigorous parasite and dental care, rapid treatment of any secondary illness, and regular veterinary monitoring, many FeLV-positive cats enjoy good quality of life for years. And because a safe, effective vaccine exists and a reliable test is quick and inexpensive, FeLV is one of the most preventable serious diseases your cat can face.
🔍 Causes
FeLV is spread cat-to-cat through saliva, and to a lesser extent urine, nasal secretions, and milk. The main routes are mutual grooming, shared food and water bowls, bite wounds, and from an infected mother to her kittens. Kittens and young cats are far more susceptible than adults, whose immune systems can sometimes fight off the virus before it takes hold.
🛡 Prevention
Vaccination is highly effective and recommended for any cat with outdoor access or exposure to cats of unknown status. Test every new cat before introducing it to a household, keep positive and negative cats separate, and neuter to reduce roaming and fighting. Because the virus is fragile and does not survive long outside the body, it is not spread on clothing or by casual contact between households.
💊 Treatment
There is no cure. Management focuses on supportive care: prompt treatment of secondary infections, an excellent diet, parasite control, and avoiding stress. FeLV-positive cats should be kept strictly indoors — both to protect them from infections and to prevent spread to other cats. Many live comfortably for several years with attentive care and twice-yearly vet checks.
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⚕️ Medical disclaimer
- This information is educational only and is not a substitute for veterinary advice.
- Symptoms overlap between conditions — only a vet can diagnose accurately.
- Never withhold treatment or self-medicate based on information found online.
- When in doubt, call your vet. Early intervention almost always leads to better outcomes.