Feline Leukemia Virus, or FeLV, is a viral infection that affects cats. It is caused by a retrovirus that can weaken a cat's immune system, making them more susceptible to other infections and diseases. FeLV is primarily spread through saliva, urine, and other bodily fluids, often through grooming or biting. Cats infected with FeLV may not show symptoms for years, but they can still spread the virus to other cats. Regular veterinary check-ups and testing are important for early detection. Vaccination is available to help protect cats from FeLV, especially for those at higher risk.