Cats are prone to many diseases. Here are a list of some diseases which can be harmful to your cat.
FIV: FIV stand stands for Feline Immunodeficiency Virus. Unlike HIV which is transmitted via sexual contact, FIV spreads through territorial and outdoor cats who are susceptible to infection and also by bite wounds. FIV does not spread through sharing of water bowls or food but there are chances that the virus may pass from the mother to her kittens but it happens rarely.
The virus does not act immediately when it enters the bloodstream. It remains dormant in the bloodstream till it progresses to an active disease. FIV directly targets the immune system which causes the cat to have enlarged lymph nodes, inflamed gums, eye disease, weight loss, ulcers on the tongue, anemia, skin diseases. The only way you can keep your cat at bay of FIV is by keeping it indoors and having it vaccinated on time.
Leukemia: Feline Leukemia can pass through bites, sharing water bowls and food and also from living together. This discharge can spread through saliva, nose discharge and urine. Kittens are more vulnerable to this disease then the adult cats. Some cats will fall sick immediately on contracting the disease and some will take several weeks to manifest it. It can result in a system wide infections, eye diseases, respiratory tract infection, anemia, infertility, cancer. Any illness that is severe and chronic can be a sign of feline leukemia. There is no cure for leukemia but it is preventable. You need to keep the cat indoors, maintain a clean environment, restricting its exposure to other cats.