Merck Manual

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Gastrointestinal Parasites of Dogs

Gastrointestinal Parasites of Dogs

Common Name (Scientific Name)

How Contracted

Signs

Control and Prevention

Esophageal worm (Spirocerca lupi )

Dogs eat intermediate host (dung beetle) or transport host (chickens, reptiles, rodents)

Most show no signs. When present, signs include weight loss, coughing, and trouble breathing. When severe, dog has difficulty swallowing and may vomit repeatedly after trying to eat. Occasionally, death from rupture of aorta damaged by worms. Diagnosed by microscopic fecal examination, endoscopy, and x-rays.

In areas where the worm is common (southern US, tropics), dogs should be prevented from eating dung beetles, frogs, mice, lizards, or other small animals, and not fed raw chicken scraps.

Hookworms (Ancylostoma caninum, A. braziliense, Uncinaria stenocephala)

Eating infective larvae, transmission during nursing, or by direct skin penetration

A. caninum—Anemia that can be fatal and poor growth of puppies; in severe cases diarrhea with dark, tarry stools. Often no signs, particularly with other hookworm infections. Diagnosed by microscopic fecal examination.

Puppies should be dewormed on multiple occasions in the first 3 months of life. Some monthly heartworm preventives also control hookworms. Housing areas for pregnant dogs and puppies should be free of contamination and cleaned regularly.

Roundworms (Toxocara canis, Toxascaris leonina)

T. canis—commonly passed from mother to pups through the placenta. Also acquired during nursing. Both parasites acquired by ingestion of eggs or transport hosts.

Often no signs. Diarrhea, poor growth, or a distended, swollen abdomen; worms may be passed in feces or vomit. Most often diagnosed by microscopic fecal examination.

Puppies should be dewormed on multiple occasions, during the first 6 months of life. Mothers should be treated prior to giving birth to reduce transmission to pups. Monthly heartworm preventives will also prevent roundworm infection.

Stomach worm (Physaloptera species)

Dogs eat hosts (beetles, cockroaches, crickets, mice, frogs)

Stomach inflammation, which can result in vomiting, loss of appetite, and dark feces. In heavy infections, anemia and weight loss. Most often diagnosed when whole worms are found in vomitus, typically with no signs.

Several drugs from your veterinarian can be used to treat infection.

Tapeworms (cestodes)

Eating infected prey animals or fleas

Most infections have few signs. Poor absorption of food or diarrhea may occur. Most often diagnosed by observing segments in the feces or perianal area of the dog.

Control requires medication to treat the tapeworms and preventing access to prey animals so the dog is not reinfected. Flea control is also important.

Threadworm (Strongyloides stercoralis)

Infective stage in environment pene-trates skin or is swallowed; also passed via breast milk

Often no signs. Blood-streaked diarrhea, especially in hot humid weather; reduced growth rate and weight loss. In severe cases, fever and shallow breathing. Diagnosed by microscopic fecal examination.

Isolation of sick animals; thorough washing of pet living areas. Disease is more severe in animals with a weakened immune system. Several medications are available to eliminate the parasite.

Whipworms (Trichuris vulpis)

Shed in feces; become infective in 4 to 8 weeks. Infective eggs are eaten by dogs.

No signs are seen in light infection; heavy infection produces weight loss and diarrhea. Fresh blood may be seen in feces, and anemia may be present. Diagnosed by microscopic fecal examination.

Eggs are susceptible to drying out, so maintaining cleanliness and eliminating moist areas can help reduce likelihood of infection. A number of drugs are available for treatment and prevention.

*A number of antiparasitic drugs (anthelmintics) are available to treat parasites in dogs.