What it is
Feline coronavirus on its own causes no more than mild diarrhoea and spreads through faeces, especially where many cats live together. Only in some cats does the virus change inside the cat's own body and infect immune cells that carry it all over. The immune response itself then starts to damage the tissues.
The disease takes two forms. In the wet form a thick, yellowish fluid collects in the belly or the chest, so the belly swells or breathing becomes hard. In the dry form patches of inflammation appear in the organs, the eyes or the brain, so the eyes, the gait or behaviour can change.
It mainly affects young cats, sometimes after stress such as a move or neutering. It is not easy to confirm, because its signs resemble many other diseases, so a vet's tests are needed. It does not pass to people.
Signs you may notice
A cat has a fever that keeps coming back, stops eating, loses weight and turns listless. The belly may swell with fluid, breathing may become hard and the gums or eyes may turn yellow; sometimes the eyes or the way it walks change.
When to see a vet
Book a visit if a young cat has a fever, stops eating and loses weight, or its belly has swollen. If it struggles to breathe or breathes with its mouth open, a vet is needed immediately.
This is general information, not veterinary advice. For your own cat's health, tests and treatment, see a vet.