INTERNAL PARASITES

This page is designed to give you an overview of some of the internal parasites that can infect your dog and cat. If you request we can provide separate information sheets on roundworms, tapeworms and heartworms that will give you with more details.

ARE THERE DIFFERENT SORTS OF INTERNAL PARASITES OR WORMS?
There are several types of internal parasites that cause problems in dogs and cats. These include nematodes or roundworms, of which Toxocara canis (intestinal roundworm) and Dirofilaria 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 AND CAT?
Intestinal parasites are only occasionally life­threatening in adult pets, and are usually seen in debilitated animals or those that are immunosuppressed.

HEARTWORMS
A major life-threatening problem. Heartworm disease is considered to be one of the most serious conditions seen in small animal practice. Heartworm disease is transmitted by mosquitoes. 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 of heartworm infection are fatigue, coughing and poor physical condition.   Click to read more about heartworms, heartworm prevention and heartworm treatment.

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

ROUNDWORMS
Roundworms do not require an intermediate host to spread from amimal to animal. Nematodes (roundworms) are free-living in the bowel. A growing puppy or kitten infected with a large number of roundworms, can have stunted growth, serious digestive upsets and resulting excessive gas formation. These pets have a characteristic 'pot bellied' appearance. Roundworms can be transmitted from animal to animal via infective eggs shed in the feces.

TAPEWORMS
An intermediate host, the flea or some species of small rodents, is required.
Dipylidium caninum, the common tapeworm of the dog and cat, causes few problems in the adult host but can result in digestive upsets and stunting of growth in puppies and kittens. The intermediate host of Dipylidium is the flea.

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.

Cestode tapeworms are usually found in adult dogs and cats and cause few problems. Puppies and kittens 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 and cat. 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.