March 17, 2023

New study finds drug-resistant parasites are widespread in pet dogs across U.S.

Finding may have implications for Canadian domestic dogs as hookworm cases rise on this side of the border
PhD candidate Abhinaya Venkatesan, left, and John Gilleard led the study. Kirsten Glowa Kobe, Faculty of Veterinary Medicine

What are hookworms (Ancylostoma caninum) in dogs and what does it mean? Well … they are intestinal parasites that get their name from the hook-like mouthparts they use to anchor themselves to the lining of the intestinal wall. A significant number of hookworms can cause inflammation in a dog’s intestine, as well as a life-threatening decrease of red blood cells (anemia), weight loss and can even be fatal in severe cases. They are also zoonotic, causing a condition in people called cutaneous larval migrans (CLM) if the infective larvae penetrate human skin.

Researchers at the University of Calgary Faculty of Veterinary Medicine (UCVM) have published a collaborative study in the PLoS Pathogens journal showing that parasitic hookworms are resistant to one of the most important drugs. They are now widespread in pet dogs throughout the USA. 

“This is the first study to show geographically widespread drug resistance in a gastrointestinal worm of domestic dogs from anywhere in the world. Drug resistance hasn’t previously been considered a major problem for companion animal internal parasite control and so this may come as a surprise to many veterinarians,” says Dr. John Gilleard, PhD, whose research team led the study.

“It means that many routine drug treatments are now ineffective and so we need to rethink how we control this parasite and use important antiparasitic drugs in companion animals in a more sustainable way.”

image of an adult canine hookworm head

Magnified image of an adult canine hookworm head.

Pablo Jimenez Castro

This multidisciplinary study was a part of the thesis work of PhD candidate Abhinaya Venkatesan and was a collaborative effort between researchers at the University of Calgary, the University of Georgia, Northwestern University and University of California, San Francisco.

“We first identified two drug resistance mutations in the genome of the parasite, one of which has never been previously described,” says Venkatesan, lead author of the study. “We then used this molecular genetic information to screen hundreds of fecal samples from hookworm-positive dogs from across the USA. We found that over 50 per cent of the dogs were infected with drug-resistant hookworms.”

Another interesting aspect of the study was how the researchers used state-of-the-art next-generation DNA sequencing technologies to undertake the large-scale screening of canine hookworm populations.

“This work really shows the power of these new genetic technologies in diagnostics and surveillance,” says Gilleard. “It is also a great example of how fundamental discovery research can lead to translational outcomes of practical importance.

"We have used our discovery of a novel drug resistance mutation to reveal widespread drug resistance in an important parasite of pet dogs. We now really need to start to use these approaches in routine diagnostics to better target the drugs we use.”

canine hookworm infective larvae

Microscope image of canine hookworm infective larvae.

Pablo Jimenez Castro

The next step in the research is to use a similar approach to assess the current situation in the Canadian pet dog population which is currently unknown.

“A. caninum is generally thought of as a parasite found in warmer regions such as the southern USA,” says Venkatesan. “However, many dogs are brought into Canada from these warmer regions and recent evidence suggests hookworm prevalence is increasing in Canada. It will be important to determine whether this is due to the spread of drug-resistant parasites or other factors such as climate change.”

The team has recently been awarded a grant from the Zoetis Investment in Innovation Fund to help undertake this Canadian study.


Map of hookworm drug resistance data on dogs across the United States.

Abhinaya Venkatesan

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