Toxocara canis
| Toxocara canis | |
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| Adult Toxocara canis | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Nematoda |
| Class: | Secernentea |
| Order: | Ascaridida |
| Family: | Toxocaridae |
| Genus: | Toxocara |
| Species: | T. canis |
| Binomial name | |
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Toxocara canis Werner 1782 |
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Toxocara canis (also known as dog roundworm) is worldwide-distributed helminth parasite of dogs and other canids. Toxocara canis is gonochoristic, adult worms measure from 9 to 18 cm, are yellow-white in color, and occur in the intestine of the definitive host. In adult dogs, the infection is usually asymptomatic. By contrast, massive infection with Toxocara canis can be fatal in puppies.
As paratenic hosts, a number of various vertebrates, including humans, and some invertebrates can become infected. Humans are infected, like other paratenic hosts, by ingestion of embryonated T. canis eggs. The disease (called Toxocariasis) caused by migrating T. canis larvae (toxocariasis) results in two syndromes: visceralis larva migrans and ocularis larva migrans. Owing to transmission of the infection from the mother to her puppies, preventive anthelmintic treatment of newborn puppies is strongly recommended. Several antihelmintic drugs are effective against adult worms, for example pyrantel, fenbendazole, selamectine, etc.
The adult canis has a round body with spiky cranial and caudal parts, covered by yellow cuticula. The cranial part of the body contains two lateral alae (length 2–3.5 mm, width 0.1 mm). Male worms measure 9–13 by 0.2–0.25 cm and female worms 10–18 by 0.25–0.3 cm. T. canis eggs have oval or spherical shapes with granulated surfaces, are thick-walled, and measure from 72 to 85 μm.
Eggs are deposited in feces of dogs becoming infectious after 2–4 weeks. Dogs ingest infectious eggs allowing the eggs to hatch and the larval form of the parasite to penetrate through the gut wall. In young dogs, the larvae move through the body via the bloodstream by penetrating a blood vessel in the gut wall. Once in the lungs, the larvae enter into the alveoli and crawl up the trachea. The larvae are then coughed up and swallowed leading back down to the small intestine. The larvae encyst in gut wall tissues within older dogs. The cysts can reactivate in pregnant females to infect puppies either through the placenta in utero or the mammary glands in colostrum and milk. Another possible route of infection is the ingesting of paratenic hosts that contain encysted larvae from egg consumption thus completing the life cycle for the parasite to re-infect its definite host, the dog.
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Wikipedia