Treatment-resistant worm spreads among dogs in the U.S.: Canadian study

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Genetic mutations in a parasite that clings to the intestinal wall of dogs with its hook-shaped beak allow it to resist one of the primary drugs used to treat it, a Canadian study warns.

Researchers at the University of Calgary found this resistant form of hookworm in half of the U.S. dog feces samples they analyzed.

It's unclear whether this resistant worm is also spreading to Canada, but the researchers recently obtained funding to continue their work on this side of the border.

The study's authors identified two mutations in the parasite's genome that allow it to resist treatment, including one that had never been documented before.

"This is not really surprising," said Dr. Christopher Fernandez-Prada, a parasite specialist at the University of Montreal's Faculty of Veterinary Medicine. "In recent years, especially in the United States, there has been very heavy use of the preventive product. Resistance is not unique to bacteria (so) it was expected for a long time."

Because the worm is so prevalent in the environment, it's relatively easy for a dog to become infected with a parasite that has survived exposure to these molecules, he explained.

The disease is transmitted through larvae that hide in the soil after being expelled in infected feces. The larva pierces the skin of its host to restart the life cycle. Hookworms can also infect humans and cause skin lesions.

Hookworms have long been confined to warmer regions like the southern United States. However, Dr. Fernandez-Prada said that its spread to Canada may be facilitated because Canada imports large quantities of dogs from the United States.

After disasters like Hurricane Katrina, he said, "Canada is always a taker" for animals looking for a new home.

There is also evidence that the parasite has begun to migrate north, possibly due to global warming. A map published by the Canadian researchers shows that infected samples have been found, sometimes in large quantities, in New York State, Vermont, New Hampshire and Maine – all areas bordering Quebec and Atlantic Canada.

Tourists travelling to the United States with their four-legged friends are therefore advised to consult their veterinarian before leaving and then to use their best judgment.

"We're trying to educate owners to change their behaviour and that of their pets, to avoid going to places where the risk is a little higher," said Dr. Fernandez-Prada, who does a lot of training for veterinarians in the province.

Sandy areas, such as beaches, are particularly prone to the spread of the parasite if dogs carrying the resistant worm and who have not been properly dewormed have frequented them, he continued.

The concentration of parasites, for obvious reasons, may also be somewhat higher in dog parks.

"You need a place where there is a high concentration of feces from other dogs," said Dr. Fernandez-Prada. "You can't eliminate the risk entirely, but you shouldn't panic either."

The new study, he said, doesn't show that hookworm is now completely resistant to all treatments but rather that resistance is more widespread than previously thought.

Veterinarians still have effective drugs available to combat it, Dr. Fernandez-Prada said.

"We have an emerging problem, but we still have tools and solutions," he said.

The findings were published in the medical journal PLoS Pathogens. 

- This report by The Canadian Press was first published in French on March 31, 2023