New World Screwworm: Spread, Threat, and Control in North America
Canada just stopped importing some livestock from Texas. It’s all because of the New World screwworm . That thing is a nasty flesh-eating parasite. If left alone, it kills animals.
US authorities found two infected calves in southern Texas. That discovery kicked off this whole mess. And now there are real worries that this isn't just stuck in Texas anymore. It’s moving through Mexico and Central America. Heading further north.
The Canadian Food Inspection Agency—the CFIA—made the call. They won't let cattle or horses into Canada if they were in Texas within twenty-one days before crossing the border. That’s the rule now.
This all happened after the USDA confirmed those two cases of infestation. Southern Texas is huge for cattle production, so this isn't just some small farm issue. It hits the whole industry hard.
Texas Governor Greg Abbott declared a state of disaster right away. He warned that this parasite poses an imminent threat to their agriculture. Imminent threat . You can feel that urgency.
What exactly is this screwworm?
People usually think it’s some kind of worm. It isn't. It's the larval stage of a parasitic fly. Not really a worm at all.
These larvae aren't just munching on dead tissue, like regular maggots. They attack living flesh. Female flies lay eggs in cuts or open wounds. Sometimes even on humans. Once those hatch? Hundreds of larvae burrow into the living tissue using sharp hooks. It causes terrible infections and massive tissue damage. Eventually, death.
It hits cattle, horses, sheep, goats, pigs—wildlife, pets too. Humans can get it, though it’s rare. Still, in livestock, it just weakens them fast. Economic losses are huge.
Detection and Spread
The first detection was a three-week-old calf near the Mexico border, La Pryor. Then another one showed up nearby in Zavala County. Just two spots to start the chain reaction.
US officials set up a twenty-kilometer control zone around where they found things. They imposed quarantines and started intense surveillance. Trying to slow it down.
But there’s something interesting about the spread. Officials think this is part of a bigger movement north through Central America and Mexico. It's moving with the climate, you know?
Canadian officials say, for now, the risk isn't huge over there. Screwworm flies like warm, humid places. Historically, they struggled in the cold regions. But that doesn't make it safe to ignore. Infected animals can carry the pest across borders before anyone even notices symptoms.
Farmers are being told to check their livestock constantly. Look for weird wounds, discharge, any sign of infestation. Pet owners heading to Texas? They need to watch what they bring in too.
Control Methods and Economic Impact
There is a known fight against this thing. The Sterile Insect Technique. It works surprisingly well. Scientists breed millions of male flies. Sterilize them. Release them into the wild. When these sterile males mate with females, nothing happens. No offspring. The parasite population just slowly collapses over time.
That method actually wiped out screwworms from the US back in 1966. It’s been used again and again to keep outbreaks contained. Now they plan to release hundreds of millions of those sterile flies. And deploy detection dogs, too. Trying to catch what’s already there.
The US and Canada share a massive trade relationship with livestock. Over half a million cattle crossed from the US into Canada in just 2025. That trade is huge.
If this thing keeps spreading further north? It could seriously disrupt that cattle trade. Costs for farmers would skyrocket. The whole North American agricultural industry faces major challenges. Authorities on both sides of the border are currently racing against time to keep this parasite from taking hold during the summer heat when it spreads fastest.
Written by Gree News Team — Senior Editorial Board
Gree News Team covers international news and global affairs at Gree News. Our collective of senior editors is dedicated to providing independent, accurate, and responsible journalism for a global audience.
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