Catching worms from pets: real risk or far-fetched?

February 15, 2012
By: Phyllis DeGioia
For The VIN News Service

Photos courtesy of the CDC

Common intestinal parasites found in dogs and cats that may be transmitted to people are — shown above in the following order — the hookworm, roundworm and tapeworm.

Larger-than-life visuals of the intestinal parasites featured on the Animal Planet's “Monsters Inside Me” could belong in a horror film despite the show's educational bent. Where wormy parasites are part of an average workday, a question from those who watch the show has emerged:

Do veterinarians and their staff need to be dewormed regularly?

It's a concern veterinary technicians recently shared with their boss, Dr. Amy J. Wolff in St. Peters, Mo.

“I am always chiding and reminding the staff members to keep food out of the lab, and wash their hands. It’s a busy practice so lunch is often taken on the run,” Wolff said. In addition to private practice, Wolff is also the program director of a veterinary technology program at nearby Sanford-Brown College.

“We stress/teach safe working practices, so all my lectures spill over into the clinic where I practice,” Wolff said. “That’s what prompted the discussion, one of my many long-winded diatribes about contracting parasites and zoonotic diseases. One of the techs asked if I (de)wormed myself, and that got us wondering if others do the same.”

Wolff used to take the antiworm medication mebendazole because she worked, volunteered and traveled in areas where she encountered unsanitary conditions and diagnosed parasite carriers. She stopped because she now teaches four out of five work days.

To satisfy her staff's curiosity, Wolff posed the question to colleagues on the Veterinary Information Network (VIN), an online community for the profession.

While jokes were inevitable — “Do I give myself worms? I hope not” — some responses were serious, reflecting the veterinary profession's occupational exposure to parasites. Some veterinarians said their physicians treat them for worms on a regular basis. Others said they consider deworming after traveling to exotic locales and having gastrointestinal (GI) problems.

Whether traveling or at home, there’s no avoiding parasites. Dogs and cats can carry infestations, and those worms are trundled into the clinic. Exposure to parasites increases when litter boxes are cleaned and dogs are taken out for elimination.

Does this mean veterinarians and their staff need to be dewormed as a precautionary measure?

"In my opinion, no," said Scott Weese, DVM, ACVIM, a co-author of the Ontario Veterinary College Centre for Public Health and Zoonoses’ website Worms & Germs Blog, which promotes safe pet ownership. “The incidence of GI parasitism in people in developed countries is extremely low, particularly in adults. There is no evidence that I'm aware of that vets are at any higher risk for GI parasitism than the general public. There's no evidence that routine deworming of people in the general public is indicated, so that would extend to vets.”

In most cases, a person has to ingest parasite-laden feces in order to contract worms from an animal. Good common sense and hygiene greatly reduces the risk, Weese said.

“The risk is never zero,” Weese said, “but I'm not convinced it's any higher for a vet than someone that goes for a walk in the park.”

Veterinarians who encounter food animals are most at risk of contracting Cryptosporidium, a protozoan parasite that, unlike worms, is not susceptible to antiparasitics, Weese said.

“In small animals, there is potential exposure to a wide range of parasites but limited risk,” Weese said. “Most of the high-profile ones like roundworms are not immediately infective. You have to ingest old feces where eggs have had a chance to become infective. The incidence of clinically relevant roundworm infection in adults seems to be very low, again with no indication vets are at higher risk."

Intestinal worms in dogs and cats with the most zoonotic potential are:

Roundworms (Toxocara canis and Toxocara cati) resemble spaghetti noodles and can grow from one to seven inches long.
Hookworms (Ancylostoma caninum and Ancylostoma braziliense) are much smaller than roundworms, usually five to fifteen millimeters in length, and are named for their vampire-like teeth that attach to the wall of the small intestine.
Tapeworms (Dipylidium caninum) are long flat worms, growing six to 24 inches in length, that attach themselves to the intestines where their egg packets can break off, appearing in feces and on the skin and hair coat around the anus of animals as small white segments resembling grains of rice.

Echinococcus is a less common genus of tapeworm with two zoonotic species: E. granulosus (cystic) and E. multilocularis (alveolar). Dogs, cats and humans can contract Echinococcus by ingesting parasite eggs via the fecal-oral route or while consuming vegetation or water contaminated with infected feces. Human cases are rare and can lead to serious medical complications.

Dipylidium caninum, however, is the most common tapeworms of dogs and cats. To contract this parasite, the host must swallow an infected adult flea containing a cysticercoid, or larval tapeworm. Dr. Kenton Flaig, of Portville, N.Y., knows of at least one instance where this has happened to a pet owner.

“I had a client who picked up tapes from her dogs who slept in her bed,” Flaig said by email to the VIN News Service.

Most of these worms settle in a host's intestines and cause GI problems. Transmission often occurs when a person handles soil or sand that contains aged, contaminated feces, and there's hand-to-mouth contact.

Children are most susceptible to worm infestations because they are more likely to put soiled hands in their mouths or eat before washing. Veterinary professionals need to wear gloves when handling feces and wash their hands regularly, public health experts advise.

“... Fresh feces can contaminate the coat of the pet and often sticks around long enough to let those eggs incubate into an infective form,” Flaig wrote of roundworms. “Infected fleas, flea larvae ... are infective if eaten. Bottom line is that people can and will get exposed to parasites from their pets even if they don't eat well-incubated feces.”

For veterinarians who feel the need to take antiparasitics, the question often is whether to use medications they have in their practices or go to a physician.

The U.S. Centers for Disease Control and Prevention (CDC) takes a dim view of veterinarians treating themselves. Press Officer Candice Burns Hoffman said that according to CDC experts on parasitic zoonoses, veterinarians treating themselves with veterinary medications — for worms or any other reason — is inappropriate.

“Treatment for parasitic infections varies with the species of parasite and would be based on parasite-specific diagnosis made by the health care provider,” Hoffman said. “Infection with zoonotic parasites can be prevented by practicing good hygiene and using appropriate protective equipment and technique.”

Weese offers this advice for anyone in close proximity to animals: “My five top tips for avoiding zoonotic parasites are: wash your hands, don't eat feces, wash your hands, don't eat feces and wash your hands.”

Editor's Note: This article was amended from its original, which overstated the zoonotic potential of whipworms. The VIN News Service re-edited the piece in consultation with veterinary parasitologists who suggested several clarifications.

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