Intestinal parasites can certainly cause bloating and diarrhea, but so can many other disease processes. Piperazine only covers roundworms and there are many other parasites that an outdoor cats can pick up. The itching and scratching could certainly be from fleas, and fleas will give your cat tapeworms. I would see your vet to make sure that it is something simple or something more serious. If your cats has wounds, they should be cleaned, hydrogen peroxide is fine, but he may need oral antibiotics beacuse bite wounds are very common in outdoor cats. If money is tight, do not ever let your cat go outdoors. The average ligfe span of an outdoor cat is 3 years of age, and they are always getting into troble that will end with a vet visit. The average life span for an indoor noly cat is 17 years of age.