Marlin is positive for FeLV. Feline Leukemia Virus (FeLV), is a virus that attacks the immune system of a cat. It isn’t a form of cancer but is actually a virus that weakens the immune system. Cats with FeLV can live normal, happy healthy lives — they just have a much shorter life expectancy than FeLV negative cats. They can only live with other cats who are also FeLV positive since it is socially transmitted.