If you suspect your pet is ill or suffering from a sudden fever, lack of appetite, lost weight, or a changing eye condition than you should check your pet. You can do a test at home with the Witness FeLV-FIV test. https://www.zoetisus.com/products/diagnostics/virachek-felv-_feline-leukemia-virus-_felv_-antigen-test-kit_.aspx