Feline Leukemia: This virus is the cause of a number of fatal conditions not strictly classified as leukemia. Some of them are various forms of cancer and malignancy; the virus suppresses the immune system and leaves cats susceptible to other infections and diseases. Cats transmit Feline Leukemia to one another through saliva, which may happen during mutual licking and grooming or by sharing food and water bowls. Sharing litter boxes, through the urine and feces can also spread this virus. Your veterinarian can test your cat for this disease by drawing some blood, which we recommend here on all stray and/or outdoor cats. When starting this vaccine, there is an initial dose given followed with a second dose is given 3 weeks later. The vaccine is then repeated once annually.