Signs seen include vomiting and diarrhoea (which is often bloody), fever, reluctance to eat and a severe depression. As a result of these signs cats can very rapidly become dehydrated and anaemic. Often the number of white blood cells becomes very low.
Unvaccinated kittens are particularly vulnerable and the disease can be rapidly fatal.
If a cat is infected during pregnancy, the virus can cause damage to the brain of the developing kittens (cerebellar hypoplasia).
Once infected, a cat can carry the virus for months, and during pregnancy it can be transmitted to the unborn kittens. The virus may persist in kittens infected in utero.