Feline disease refers to infections or illnesses that affect cats. They may cause symptoms, sickness or the death of the animal. Some diseases are symptomatic in one cat but asymptomatic in others. Feline diseases are often opportunistic and tend to be more serious in cats that already have concurrent sicknesses. Some of these can be treated and the animal can have a complete recovery. Others, like viral diseases, are more difficult to treat and cannot be treated with antibiotics, which are not effective against viruses.