Only a veterinarian professional can diagnose a cat like the British Longhair with the FeLV or Feline Leukemia Virus. The FeLV virus affects cats only and is not contagious to other animals or people. One of the best ways to fight FeLV is to prevent it with vaccinations and to test your cat routinely to catch it early. The symptoms of FeLV include pale gums, yellow coloring of the mouth and whites of the eyes, enlarged lymph nodes, bladder infections, etc. In order to diagnose your cat your vet will need to administer a simple blood test called ELISA, which can identify the FeLV proteins. This test is very good at identifying FeLV in early stages. A second test known as IFA can be administered to detect the progression of FeLV in infected cats. For additional information regarding testing, please contact your Firth Veterinary Hospital.