carrier

Cats can become carriers of some viruses once infected. Depending on the virus it may become 'latent' (inactive) and reactivate when the cat is stressed. If the virus is 'shed' (excreted from the body) it can then infect other cats.

SOURCE: cats.org.uk

A cat (organism) whose genotype includes a recessive allele that causes disease, but who does not have the disease themselves.

SOURCE: cat-world.com.au