U.S. halts Mexican cattle imports over screwworm fears. Experts warn Canada could be at risk without stronger surveillance and preventive measures.
In a significant move, the United States has once again suspended imports of live cattle from Mexico after detecting screwworm infestations—flesh-eating larvae that pose serious health threats to both animals and humans. This decision, announced on Sunday, has reignited conversations around the pest’s alarming northward spread and its potential to reach Canada.
Canadian Experts Sound the Alarm
Jacob Shelley, associate professor at Western University’s School of Health Studies, warns that Canada should be vigilant. “Anytime we have a pest that can disrupt entire systems, it deserves serious attention,” he stated in an interview. His concerns are echoed by other health professionals who believe Canada’s current systems might be ill-prepared to deal with such an invasive threat.
The Global Spread of a Flesh-Eating Fly
Screwworm, a parasitic fly native to warmer climates, has spread steadily northwards, making its way from South America to Mexico. In February, Costa Rica declared a national emergency following a surge in screwworm cases. Even Canada hasn’t been immune—one recent case involved a Canadian traveler returning from Costa Rica.
The U.S. initially detected the parasite in cattle from Mexico in late 2023 and had temporarily restricted imports. Although the ban was lifted in February after introducing stricter screening protocols, it has now been reinstated due to renewed concerns.
A Deadly Parasite with No Cure
Unlike viral or bacterial infections, screwworm infestations can’t be treated with vaccines. According to Dr. Isaac Bogoch, an infectious disease specialist at Toronto General Hospital, the parasite’s larvae feed on live tissue, making infections incredibly destructive. “It can cause serious harm and even death in any warm-blooded animal it infests,” he said.
Efforts to Stop the Northward March
Historically, scientists contained the screwworm by deploying a “sterile insect technique” in Panama—releasing sterilized flies to prevent reproduction. This method had helped form a biological barrier that kept the parasite from moving northward. However, that barrier has now been breached.
In response, the U.S. has begun releasing sterile flies in southern Mexico in hopes of reestablishing control and halting the pest’s migration.
Is Canada Prepared?
Preventing the entry of screwworm into Canada might prove challenging. Flies are prolific breeders, and Canada’s large-scale agricultural practices—where animals and humans regularly interact—could accelerate the spread if an outbreak occurs.
Shelley warns that Canada’s monitoring infrastructure, while present, might not be robust enough to stop a rapid spread. “Without immediate restrictions or improved inspection protocols, we’re at risk,” he emphasized.
The Stakes for Canadian Agriculture
If screwworm were to establish a presence in Canada, the consequences could be severe. Cattle may need to be culled, disrupting supply chains and driving up beef prices. The broader economic impact could mirror the devastation seen in past U.S. outbreaks, where the livestock industry took decades to recover.
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