One of the most common ailments in dogs is worm infestations. Worms are parasites that live inside the animal and cause different problems, depending on the type of worm your pet has. Generally, there are five major types of worms, roundworm, tapeworm, hookworm, whipworm and the dreaded heartworm. All of these can cause light to serious complications and should never be left untreated. First, let’s look at the different types of parasite and what they do.