🇲🇽🇺🇸 Tensions Rise as U.S. Shuts Border to Mexican Cattle Over Flesh-Eating Screwworm
A new dispute has erupted between Mexico and the United States after the U.S. Department of Agriculture (USDA) announced it would re-close the border to cattle imports from Mexico due to a newly reported case of the New World screwworm (NWS) — a dangerous flesh-eating parasite that infects livestock and wildlife.
Mexico's President Claudia Sheinbaum called the move “completely exaggerated,” especially given that the USDA had only just begun reopening select livestock ports following months of closures. The latest shutdown comes after just one confirmed screwworm case in the state of Veracruz, nearly 370 miles south of the U.S.-Mexico border.
🐛 What Is the New World Screwworm?
The New World screwworm (Cochliomyia hominivorax) is a parasitic fly species native to the Americas. The female fly lays her eggs in open wounds or orifices of warm-blooded animals. Once the eggs hatch, maggots burrow into the host’s flesh, causing extreme pain, injury, and — if left untreated — potentially death.
The parasite was successfully eradicated from the United States decades ago through an intensive campaign that used sterilized flies to break the breeding cycle. However, the screwworm has made a dangerous comeback in Central America since 2022, and has been pushing north through Mexico ever since.
📉 Mexico Pushes Back on U.S. Ban
Speaking at a press conference on Thursday, President Sheinbaum said the U.S. decision to reimpose cattle import restrictions after a single case was discovered is “not proportionate” to the threat level. She emphasized that Mexico has been aggressively fighting the pest through a national eradication program in place since November 2021.
“Yesterday, when we learned there was a case — just one case — in Veracruz, we believe the decision to re-close the border was completely exaggerated,” Sheinbaum stated.
According to Mexico’s agriculture ministry, there are currently 392 active screwworm cases within the country, but Sheinbaum insists the government is fully engaged in controlling the outbreak.
🧪 Why Is the U.S. Concerned?
The U.S. Agriculture Secretary, Brooke Rollins, defended the decision, stating that although trade with Mexico is important, the integrity of the U.S. cattle herd comes first.
“We are pausing the planned port reopenings to further quarantine and target this deadly pest in Mexico,” Rollins said in a statement. “We must see additional progress combatting NWS in Veracruz and other nearby Mexican states before we move forward.”
The USDA had previously reopened one Arizona port on Monday following assurances from Mexico about containment. However, the new case prompted an immediate pause on reopening five other ports that had been scheduled to resume livestock trade between July 7 and September 15.
Colin Woodall, CEO of the National Cattleman's Beef Association (NCBA), echoed the USDA's caution, stating that this issue presents a serious threat to American agriculture.
“The New World screwworm’s northward movement jeopardizes the safety of American agriculture, which is why Secretary Rollins paused cattle movement again,” said Woodall. “We can’t risk allowing it to reestablish in the U.S.”
🧬 A Long-Term Battle: Sterile Fly Program Rebooted
To combat the advancing screwworm threat, the USDA is reinvesting in a decades-old eradication method: sterile fly release.
A sterile insect dispersal facility is being built at Moore Air Base in Texas, and is expected to be operational by 2025. The project aims to flood Northern Mexico with sterilized male screwworm flies, effectively preventing reproduction by ensuring that mating does not lead to larvae production.
The USDA considers this strategy a long-term buffer to protect U.S. livestock herds and eliminate future outbreaks before they reach American soil.
🌎 Politics Meets Parasites
This border shutdown isn’t just about biology — it’s now a political flashpoint. Mexico sees the U.S. reaction as economically damaging and diplomatically heavy-handed, especially given that both countries rely on tight agricultural trade ties. Meanwhile, the U.S. insists it’s acting on solid science and out of necessity to prevent a devastating outbreak in American farms and ranches.
With screwworm cases increasing and border tensions mounting, both nations now face a difficult balancing act: how to protect public health and food security without undermining crucial trade relationships.
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