Life Cycle of a Toxocara

The Toxocara canis, a parasitic roundworm, commonly infects dogs. Considered a zoonotic parasite due to the worm's ability to transfer from its animal host to a human host, the worm poses very little danger once infection is established, according to the Centers for Disease Control and Prevention. Young children who accidentally ingest animal feces containing Toxocara canis can suffer a more serious infestation and resulting illness due to their susceptibility and young immune system, but adults generally suffer mild symptoms.

  1. Life

    • The entire life cycle of the Toxocara is accomplished with the aid of a host such as a dog, rarely a cat and occasionally a human. The worm is entirely dependent upon a host. Without a viable host the life cycle will never complete.

    Eggs

    • Shed eggs in an animal's fecal matter do not form an embryo until they are outside the body. Once outside the body, the embryonic worm begins to form within the egg. It takes around a month for the worm to grow enough within the egg to infect a host, according to Mar Vista Animal Medical Center. Once the embryonic egg is viable enough to infect a host it waits to be ingested. The egg can remain viable for months or even years as it awaits a suitable host.

    Transmission

    • The dog or cat walks through contaminated, old feces or soil and the eggs attach to the fur. Once on the fur the dog normally ingests the eggs through the daily ritual of grooming. Once ingested the egg is transported through the digestive system of the animal. When the egg reaches the environment of the intestine it hatches.

    Larvae

    • Once the egg hatches within the intestinal tract the larva begins to burrow out of the intestines to find a place within the dog's body to take up residence. Within a dog the larva enjoys taking up residence on the canine's liver. As the larva grows it moves to the pet's airways and lungs. Once in the airway the dog will cough in order to clear the blockage and the worms will be hacked up into the canine's throat and swallowed. Once swallowed the worms take up residence in the intestines again.

    Intestines

    • When the worms take up residence in the intestines, again, they begin to mate within a week and produce eggs. This begins the life cycle all over again. Once within the intestines the adult worms will mate until their death. The worm's entire life cycle once inside of a host averages four to five weeks.

    Pregnant and Nursing Females

    • If a female dog is pregnant then the larvae will migrate to the dog's uterus to infect the newborn puppies. Nursing females can transmit the larvae through their mammary glands while nursing their young pups.

    Humans

    • Humans become infected with Toxocara when they accidentally ingest the eggs by coming into contact with the eggs through contaminated soil or fecal matter. The worm's lifespan once inside a human varies little from its life in a dog or cat.