Roundworms are present in the kitten when it was born. However, a good breeder usually will be able to treat the mother so as to lessen the roundworms from growing too much inside the kitten. In more mature cats, cat worms can be prevented by giving the cat daily doses of minced, fresh garlic in the diet of the cat. This garlic is able to kill roundworms as well as parasites and tapeworms. Other preventions include regular use of flea prevention, daily grooming, and keeping the bedding clean. However, when the stools of the cat are showing symptoms, it is better to get to the vet fast.