Ascarids are the most frequent
worm parasite in dogs and cats. There are two
species that commonly infect dogs: Toxocara canis and Toxascaris leonina. Adult
roundworms live in the stomach and intestines and can grow to 7 inches (18 cm)
long. A female may lay 200,000 eggs in a day. The eggs are protected by a hard
shell. They are extremely hardy and can live for months or years in the
There are four ways dogs can become infected with roundworms. Prenatal
infection occurs when the larvae migrate through the placenta in utero. Almost
all puppies are infected in this manner before birth. Mother’s milk can also
transmit ascarids. In addition, puppies and adults can become infected by
ingesting eggs in the soil. And finally, dogs can acquire the eggs by ingesting
a transport or intermediate host, such as a mouse or other rodent.
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The life cycle of T. canis in young puppies is as follows: Eggs entering
through the puppy’s mouth hatch in her stomach. The larvae are carried to the
lungs by the circulatory system. Here they break through the capillaries into
the air sacs, sometimes causing bouts of coughing and gagging. Once in the lungs, the
larvae crawl up the windpipe and are swallowed. Back in the intestines, the
larvae develop into adult worms. The adults pass eggs
that become infective in soil in three to four weeks.
Dogs older than 6 months develop an acquired resistance to ascarids. Few, if
any, larvae complete the life cycle. Most come to rest in various body tissues,
where they encyst. While encysted, they are protected against the dog’s
antibodies and also the effects of most dewormers. (Interceptor is an
exception. This dewormer has some effect on encysted larvae.) During pregnancy, however, encysted
larvae are activated and migrate to the placenta and mammary glands. Deworming
the dam before pregnancy reduces the burden of migrating larvae but does not
eliminate all puppy infestations because there are still encysted larvae in the
Ascarids rarely cause symptoms in adult dogs; in puppies older than 2
months, they usually produce only mild intermittent vomiting and diarrhea. Worms maybe found in
the vomitus or passed in the stool. Typically, they look like white earthworms
or strands of spaghetti that may be moving.
In very young puppies, a heavy infestation can result in severe illness or
even death. These puppies often fail to thrive, have a dull coat and a
pot-bellied appearance, and are anemic and stunted in growth.
Treatment: Nemex or Strongid (pyrantel pamoate suspension) is an excellent
dewormer for nursing pups because it is safe and active against both ascarids
and hookworms. Puppies should be
dewormed by 2 weeks of age-before they begin to pass ascarid eggs and
contaminate the environment. Repeat the treatment at 4, 6, and 8 weeks of age.
The purpose of retreating is to kill worms that were in the larval stage during
the first dewormings. Subsequent treatments are indicated if eggs or worms are
found in the stool.