Parasites and Bacteria

The threat from parasites varies enormously, according to where you live and whether or not your cat has access to the outdoors. External parasites such as fleas and ticks are not only irritating in themselves.

They act as carriers for other parasites. The common cat tapeworm, Taenia taeniformis, is brought into the intestines when a cat grooms itself and swallows a flea.

Toxoplasma is transmitted when a cat eats meat harboring the parasite; this meat is most often wildlife, such as birds or rodents, but not always; any undercooked meat is potentially hazardous.
 
Yet another parasite, the waterborne Giardia, has become more widespread recently, and a cat can contract this from drinking apparently clean water outside.