'Internal parasites' is a fairly polite way of saying worms. Hookworms, whipworms, roundworms, tapeworms can all infect your cat. In fact, most kittens are born with roundworms and hookworms that are transmitted from their mothers. The mothers pick them up from ingesting eggs found in soil. Treatment for these should accompany your kitten's first vaccination. Fleas are the major transmitters of tapeworms. The worms get into a cat's system when the cat ingests the flea in the process of grooming. You can see signs of these parasites in your cat's stool. They look like tiny grains of rice. If your cat has one or more of these worms, symptoms can include diarrhea, a dull coat, or change in appetite. The cat may even develop a pot belly. Internal parasites can be treated easily, but it's safer to have your vet determine the type of worms present and prescribe the correct medication.