Heartworms and roundworms are not the same. Mosquito bites can transmit microscopic heartworm larvae (microfilariae) from an infected to an uninfected dog. Those larvae then migrate throughout the body, maturing as they go. Eventually they take up residence in a dog’s heart and blood vessels within the lungs, where they make more microfilariae and can cause so much damage as to eventually result in the death of the dog without appropriate treatment. Common symptoms of a heartworm infection include coughing, difficulty breathing, exercise intolerance, and weight loss. Cats can also be infected with heartworms, although the disease that develops is a little different than what is seen in dogs. Thankfully, heartworm infections are easily prevented through the use of oral or topical medications given once a month, all year.
Roundworms, on the other hand, are intestinal parasites that can cause vomiting, diarrhea, and weight loss. They are most commonly diagnosed in puppies that have not been thoroughly dewormed. Puppies can be infected while they are still developing in the uterus or from suckling milk that contains roundworm larvae. Adult dogs can also become infected when they eat a small amount of dirt containing roundworm eggs or an infected prey animal (e.g., a rodent). Many types of deworming medications are effective against roundworms including products that contain pyrantel pamoate and fenbendazole.