Following the United States’ decision to suspend imports of live cattle from Mexico due to a screwworm outbreak, Canadian experts are sounding the alarm over the potential threat to Canada’s livestock and public health systems. The flesh-eating parasite, already confirmed in parts of Central and South America, has now sparked serious concerns among Canadian health and agriculture authorities.
Jacob Shelley, a professor of health sciences at Western University, told CTVNews.ca that Canada should take the risk seriously. “Anytime we have a pest that’s spreading between animals and can threaten an entire system, we ought to be concerned,” he said.
The Canadian Food Inspection Agency (CFIA) confirmed it is closely monitoring the situation. In a statement to CTVNews.ca, the agency noted that screwworm is classified as an “immediately notifiable disease” in Canada, meaning all suspected cases must be reported. Canada already prohibits the import of cattle, swine, goats, bison, cervids, and sheep from Mexico and has strict conditions on importing horses from the region.
The parasite, which is most common in tropical and subtropical climates, has reached as far north as Mexico. While Canada’s cold winters may limit the parasite’s ability to survive long-term, Shelley warned that Canadian farms and slaughterhouses, where animals and people frequently interact, could be vulnerable to outbreaks. A recent case involving a Canadian traveler returning from Costa Rica—currently under a national emergency for screwworm—shows the parasite can cross borders.
Infectious disease expert Dr. Isaac Bogoch explained that screwworm is not a typical virus or bacterial disease but a fly infestation. The flies lay eggs in open wounds or scrapes, and the resulting larvae feed on live tissue, making the infestation especially dangerous to both humans and animals.
“There’s no vaccine,” Bogoch said. “The larvae eat live tissue, not dead tissue, so they can cause significant harm to any animal they’re infesting.” He noted that a previous solution known as the “sterile insect technique”—used effectively in Panama—has been reintroduced in southern Mexico to stop the spread north.
Although Canada has infrastructure to track emerging pests, Shelley believes the system is not fully prepared to prevent the entry and establishment of such a parasite. He pointed to past agricultural pest outbreaks, such as the pine beetle, as evidence of the damage invasive species can cause. “If this were to spread, it could be more catastrophic than simply a few cattle or a few humans becoming infected,” he said. “It could affect the entire industry in Canada, so caution is warranted here.”
A screwworm outbreak in Canada could result in culling livestock and drive up beef prices, much like what the United States is already anticipating following the suspension of Mexican cattle imports. U.S. Agriculture Secretary Brooke Rollins has warned that it took 30 years for the American livestock industry to recover after a previous infestation.
While efforts to contain the parasite are being focused in Mexico and Central America, Canadian experts are urging heightened surveillance, strict import enforcement, and preventive planning before screwworms can take root north of the border.