Feline leukemia virus (FeLV) is a retrovirus that infects cats worldwide and can cause various health problems. FeLV spreads through saliva, nasal and other secretions as well as close contact between cats. Kittens and cats in multi-cat environments are most at risk. FeLV infection can lead to cancers, blood disorders, and secondary infections due to a weakened immune system. Testing can detect FeLV in the blood during early or late infection stages. Protecting cats involves keeping them indoors, vaccinating cats if possible, and separating infected from uninfected cats. Infected cats may live healthy lives for months but most die from FeLV-related illness within 2-3 years.