Gastrointestinal Parasites (Worms) in Dogs

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Overview of Common Canine Gastrointestinal Parasites

Most people are aware that their dogs have worms, but just what are these worms, where do they get them and how do you get rid of them? When dog owners talk about worms, they are really talking about all gastrointestinal parasites. And there are several gastrointestinal parasites that commonly affect our dogs.

Roundworms in Dogs

Roundworms are visible in your puppy‘s stool or vomit. They are long and thin, similar to thin spaghetti. This parasite can pass through the placenta (only in puppies), through the milk (puppies and kittens) or be ingested (puppies and kittens). Some animals become infected after ingesting another animal with roundworm eggs. It is thought that nearly all puppies are born with roundworms since they pass through the placenta. In kittens, most become infected after nursing.

The roundworm that affects dogs is Toxocara canis. The roundworm that affects cats is Toxocara cati. The roundworm Toxascaris leonina is shared between dogs and cats. The roundworm eggs are very resistant to chemicals and weather and remain infective in the soil for years, which can result in repeated reinfection.

Typically, the eggs are found on the soil or grass. As the dog or cat walks by, the eggs are picked up on the animal’s fur. During normal grooming, the animal then ingests the eggs. After reaching the stomach, the eggs hatch. The developing larvae continue to mature in the small intestines and become adults in about three to four weeks. At this point, the mature worms are able to reproduce and shed more eggs. These eggs pass out the intestines in the feces. Once in the soil, the eggs will become infective in about one week.

A variety of medications are used to kill roundworms. The most common is pyrantel pamoate. Unfortunately, this drug is only effective against the adult worms. For this reason, a second dose is recommended three to four weeks later, when the eggs that were present at the time of the first deworming are now mature. It is important to give the second dose three to four weeks after the first dose. If too much time elapses between doses, the maturing eggs will reproduce and continue to shed eggs. Even though these eggs are not immediately infective to the animal, their presence can increase the risk of reinfection later.

Whipworms in Dogs

Whipworms are another type of gastrointestinal parasite that affects dogs. The most common whipworm is Trichuris vulpis and it is a significant cause of large bowel diarrhea. The whipworm eggs are quite resistant and can live in the environment for up to five years.

Typically, a dog becomes infected after ingesting eggs from the environment. The eggs then hatch once they reach the stomach. It takes about three months for the eggs to mature to adults and being shedding eggs. The adults then burrow into the small intestine and feed on blood and tissue. The eggs are intermittently passed in the feces and become infective in about one month. Since the eggs are not shed all the time, repeated fecal examinations may be necessary to diagnose whipworm infection.

The most commonly used medication to treat whipworms is febendazole. This medication is administered for three days. Since whipworms are difficult to get rid of, additional treatment is recommended three weeks later and again three months later.

Hookworms in Dogs

Ancylostoma caninum is the most common hookworm in the dog. Ancylostoma tubaeforme is the most common hookworm in the cat. The eggs are relatively susceptible to cold weather and the eggs are usually destroyed after a hard freeze. Hookworm infection can occur as the worms pass through the placenta, are spread during nursing, penetrate through the skin or are ingested.

After ingestion, the eggs hatch in the stomach and develop into adults into about two weeks. If the larvae penetrate the skin, it takes about four weeks for the larvae to mature. Once mature, the worms begin reproducing and shed eggs in the feces. It then takes two to eight days until the eggs are infective. The adult worms attach to the lining of the small intestine and feed on blood. In a severe infection, profound anemia can occur.

There are a variety of medications used to kill hookworms. The most common is pyrantel pamoate.

Giardia in Dogs

Giardia are pear-shaped, one-celled organisms that infect the small intestine of dogs and cats. Most cases of Giardia in young animals cause explosive, watery diarrhea, dehydration, weight loss and an unkempt appearance. Adult animals are capable of harboring the infection without showing clinical signs.

The eggs are susceptible to chemical disinfection. Once ingested, the infective cysts develop in the small intestine. Diarrhea can begin as early as five days after exposure and cysts can appear in the feces one to two weeks after exposure. Most domestic animals contract Giardia from drinking contaminated pond or stream water. Treatment for clinical giardiasis is generally effective using drugs such as metronidazole for five to 10 days.

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