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Internal Canine Parasites

This is an overview of some of the internal parasites that can infect your dog. We have separate information sheets on roundworms, tapeworms and heartworms that will provide you with more details, upon request.

Are there different sorts of internal parasites or worms?
There are several types of internal parasites that cause problems in dogs. These include Nematodes or roundworms, of which Toxocara canis (intestinal roundworm) and Diarofilaria immitis (heartworm) are the main examples and Cestodes or tapeworms of which Dipylidium caninum, Taenia species and Echinococcus species are important examples. Ancylostoma species (hookworms) are also common internal parasites in many parts of the United States.

Are these infections serious in the dog?
Intestinal parasites are only occasionally lifethreatening in adult dogs, and are usually seen in debilitated animals or those that are immunocompromised.

Heartworm disease is a major life-threatening problem. Heartworm disease is considered to be one of the most important conditions seen in small animal practice. Heartworm disease is transmitted by mosquitoes.

Intestinal worms can be a serious problem in young puppies. Hookworms can cause anemia and roundworms can lead to poor growth and development.

Roundworms no intermediate host required
Nematodes (roundworms) are free-living in the bowel. If a growing puppy is infected with a large number of roundworms, they can stunt growth, cause serious digestive upsets and result in excessive gas formation. These puppies have a characteristic ‘pot bellied’ appearance. Roundworms can be transmitted from dog to dog via infective eggs.

What about tapeworms?
An intermediate host is required.

Dipylidium caninum, the common tapeworm of the dog, causes few problems in the adult host but can result in digestive upsets and stunting of growth in puppies. Dipylidium is spread by the flea as the intermediate host.

Echinococcus, another type of tapeworm, is important because it is zoonotic, meaning humans can be infected. Sheep and sometimes man can act as the intermediate hosts in which the immature forms of Echinococcus develop inside hyadatic cysts in various organs. In man, these cysts can involve the lungs or brain.

Control measures involving regular deworming and not feeding raw or undercooked meat are recommended.

Cestode tapeworms are usually found in adult dogs and cause few problems. Puppies are occasionally infected and, depending on the type of worm involved, the large number of worms can cause intestinal blockage.

Hookworms
Hookworms, particularly Ancylostoma, are one of the most pathogenic parasites of the dog. The hookworm is approximately 1/2 to 1″ (1-2 cm) long and attaches to the lining of the bowel. As a result of blood sucking, hookworms can cause severe anemia. In addition, the infective larvae can enter the host either by mouth or through the skin, particularly the feet. Eczema and secondary bacterial infection can result due to irritation as they burrow through the skin.

Heartworms
Heartworms are large worms reaching 6-14 inches (15-36 cm) long. They are primarily located in the right ventricle of the heart and adjacent blood vessels. The typical clinical signs are fatigue, coughing and poor physical condition.