Feline Immunodeficiency Virus (FIV) and Feline Leukemia Virus (FeLV) are feline-only retroviruses that cannot be transmitted to humans or other animals. Not all cats who test positive for FIV or FeLV will develop infections or symptoms that are fatal or that otherwise seriously impact their quality of life.

Though they have weaker immune systems, cats who test positive for FIV or FeLV can live fulfilling and happy lives like any other cats—and can live for many years.‍

A shelter or community cat or kitten should only be tested if she is showing signs and symptoms of illness that may be related to a compromised immune system caused by FIV and FeLV. If cats are not ill, we do not recommend testing. For shelters, we recommend advising adopters to have their new cat or kitten tested at a veterinarian rather than testing in-house prior to adoption.

Kittens under 6 months of age should not be tested, as they may test positive for FeLV or FIV even though they are rarely infected. The antibodies of these retroviruses can be passed from infected mothers through nursing and will pass through the kitten in time. Kittens should only be tested if they are above 8 months of age.

SOURCE: https://www.alleycat.org/resources/protocols-testing-feline-immunodeficiency-virus-fiv-and-feline-leukemia-virus-felv/