Some parasites can pass from pet to owner

Published: January 21, 2008

Q:Can dog and cat worms be harmful to people?

A:Although most common parasites of people, such as pinworms and head lice, only infect people, some intestinal helminths (worms) of dogs and cats can occasionally infect people, especially children. How this occurs depends on the worm species or type.

The common dog and cat ascarids (commonly called roundworms), Toxocara canis and Toxocara cati, respectively, pass eggs in an infected pet's feces. The eggs develop to the infectious form in soil and can survive in a thick-shelled egg for many years. When infective eggs are ingested by another dog or cat, adult worms develop in the intestine.

If the eggs are ingested by a child, usually when the child eats dirt from an area contaminated with animal feces sometime in the past, the larvae migrate in the child's tissues, creating severe inflammation. The larvae may go to the liver and cause damage there (visceral larva migrans), or they can go to the eye, causing a condition known as ocular larva migrans. When severe, hospitalization and treatment may be needed to control the inflammation.

Hookworms in the intestine of dogs and cats also pass eggs in the feces. Once in the environment, the larvae of hookworms hatch out of the eggs and crawl around seeking another pet to infect. Hookworm larvae can infect dogs and cats directly by penetrating the skin. When a person inadvertently comes in contact with the larvae in the soil, the larvae penetrate the person's skin and begin to migrate, creating linear tracts of inflammation, an itchy condition called cutaneous larva migrans. A dermatologist can recognize the characteristic lesions and prescribe topical treatment to alleviate the condition.

Some tapeworms of dogs and cats, such as the flea tapeworm Dipylidium caninum, can infect people. In this case, the source of infection is a flea that acts as an intermediate host. Dogs and cats are infected with "flea” tapeworms when they ingest fleas during grooming. If a person, usually a child, inadvertently ingests an infected flea, the tapeworm can develop in the intestine, causing mild gastrointestinal discomfort in the child and great psychological stress to parents when pieces of the tapeworm are discovered in the diaper or stool of the child.

Fortunately, the common parasites of dogs and cats that can infect people can be prevented with routine veterinary care. Recommendations are that all pets older than 6-8 weeks should be maintained on monthly parasite-control products that protect against infection with roundworms, hookworms and fleas that serve as a source of tapeworms, as well as other common parasites of pets including heartworms, whipworms and ticks. Doing so protects the pets from parasitic diseases and also protects the people with whom those pets live. For more information, go online to www.petsandparasites.org, a site developed and maintained by the Companion Animal Parasite Council.

This column is provided by the faculty of Oklahoma State University Veterinary Hospital. E-mail questions to dvm oncall@postoffice.cvhs.okstate.edu. Watch the column for answers to questions.

Comments