Dog illness can often be the result of infection by parasitical worms. There are several types of parasites that can infect your Bull Terrier. The symptoms of worm infestation are often similar to those of other illnesses. Here are some of the worms that can affect your dog, and their symptoms. 

Roundworms

Are the most common type of dog worm. They infect the intestines and can cause a pot-bellied appearance. Puppies can contract this infection from their mothers, whether though her milk or while still in the womb. Dogs can also catch roundworm by eating an infected animal or by ingesting infected soil; roundworm eggs can live in soil for years. Roundworms can be seen with the naked eye. Their symptoms include diarrhea, vomiting, dull coat, weight loss, and the aforementioned pot-bellied appearance.

Hookworms

Also live in the intestines, and they are contagious to humans. Hookworms suck blood from their victims; they can cause intestinal bleeding, anemia and death. Unlike roundworms, hookworms cannot by seen with the naked eye. A dog with hookworm might have bloody stool; he'll experience anemia, weight loss, pale gums, diarrhea and low energy levels.

Tapeworms

Are another common parasite that, like the roundworm, can be seen with the naked eye. They get their name from their long, flat, tape-like appearance; in fact, a tapeworm grows in segments, and these segments break off inside your dog's intestines and can be seen in his stool. Tapeworms are spread by the ingestion of infected fleas. Symptoms include vomiting, nervousness, anal itching, vomiting and weight loss.

Whipworms

Are long, whip-like worms that live in your dog's intestines and are not visible to the naked eye. They attach themselves to the intestinal wall and, like roundworms, feed on your dog's blood. This can cause intestinal bleeding. Other symptoms of whipworm infection can include anemia, weight loss, excessive flatulence, bloody diarrhea and lack of energy.

Heartworms

Infect your dog's heart and lungs and can cause serious dog illness. They are spread by mosquito bites. Heartworm infection can be deady; it's difficult to treat and many dogs succumb to the dangerous complications that come with treatment. Luckily, heartworm infection is easily preventable with a regular dosage of the drug ivermectin.

Heartworm infection occurs most often during the warm months, when mosquitoes are most active. The worms destroy the tissues of your dog's heart, which can lead to congestive heart failure and death. Heartworm symptoms can develop slowly over a long period of time, sometimes years.

The first symptom of heart worm is usually a mild cough. This cough gradually worsens and becomes quite severe. It will be accompanied by fatigue and labored breathing. Heartworms can spread to your dog's liver as well; if this happens, he'll experience jaundice, loss of appetite and collapse. He'll also display other symptoms typical of worm infestation, including a pot-bellied appearance, low energy levels, dull coat and weight loss.

Preventing Dog Worm Infection

You can prevent dog illness caused by worm infestation by seeing your vet regularly. Keep your dog away from feces and avoid exposing him to strays or dead animals. Keep his living area clean, and practice good hygiene yourself by washing your hands after handling your dog.