If you have a dog, then you need to know about parasites. Dogs are the frequent victims of a number of internal parasites or worms such as roundworms, hookworms, and coccidia. In most cases, early diagnosis and treatment of parasitic infections can prevent the development of any significant symptoms. Dog parasite infections may cause any or all of the following symptoms: diarrhea, weight loss, dull, dry hair; blood stools, and vomiting. Here is a closer look at the parasites that can affect your dog, and what you can do to keep him healthy.