Canada temporarily halted imports of livestock from Texas after the U.S. confirmed new New World screwworm cases in South Texas. Texas Gov. Greg Abbott declared a state of disaster, calling Canada’s response “more political than science-based,” as federal and
The disruption started quietly—then moved fast enough to rattle an industry.
On June 5, Canada announced a temporary restriction on livestock entering the country from Texas after U.S. officials confirmed New World screwworm larvae in South Texas cattle. The parasite is known for burrowing into living tissue, causing painful, foul-smelling wounds and potentially deadly damage through secondary infections.
For Texas, where the cattle industry is a $15.5 billion cornerstone, the timing is what sharpens the stakes. Just days earlier, the governor had escalated the response: Texas Gov. Greg Abbott declared a state of disaster over the “imminent threat” posed by the screwworm.
Canada’s move was specific—and broad enough to hurt.
The Canadian Food Inspection Agency said it would temporarily halt imports of livestock, including horses, from Texas. The restriction applies to animals originating from or present within the state of Texas within 21 days before they try to enter Canada. according to the June 5 agency news release. The agency also said New World screwworm is not currently in Canada.
The Canadian agency said, “will continue to work closely with U.S. counterparts to assess developments and adjust measures as needed.”
In the U.S., the confirmed cases were close together and recently detected.
On June 3, the U.S. Department of Agriculture identified a 3-week-old calf in South Texas with screwworm larvae in its umbilical area, marking the first case in the country after its spread from Mexico. On June 5, USDA confirmed a second case in a 1-month-old calf 5.6 miles away.
New World screwworm flies—about the size of a housefly—lay eggs inside warm-blooded animals’ open wounds or body openings. including eyes. nose or mouth. After the eggs hatch, larvae burrow into flesh and feed on living tissue. Once grown, screwworms move into the soil and re-emerge as mature flies, restarting the cycle.
The medical danger is part of what drives the urgency on both sides of the border. The U.S. Centers for Disease Control and Prevention says screwworm can cause serious and often deadly damage due to secondary infection or other illnesses.
Even for farmers, the concern isn’t just whether an outbreak spreads—it’s whether it triggers immediate restrictions that cut off markets.
Canada has already banned most livestock from Mexico to prevent screwworm’s spread. And Canada is the United States’ largest agricultural importer. supplying upwards of $3 billion in live animals and other animal products in 2024. according to USDA data. USDA data did not specify how much Texas provides to Canada. but Texas is the United States’ largest beef and cattle producer.
Abbott challenged the Canadian response—straight to the heart of a fast-moving dispute.
On June 5, Abbott declared a state of disaster over the “imminent threat” posed by screwworm. Andrew Mahaleris, a spokesperson for Abbott, said Canada was overreacting as Texas and USDA move quickly to contain and eradicate screwworm in a limited area of South Texas.
“This pest affects live animals and does not impact inspected Texas beef,” Mahaleris said in a statement sent June 6. “Canada’s broad restriction on Texas livestock is an overreaction that is more political than science-based.”
Canadian officials pointed to climate constraints as part of their rationale.
While many Southern U.S. states face risk due to warmer, humid temperatures that are hospitable for screwworm, Canadian officials said the parasite cannot survive Canada’s colder climates. They also said screwworm flies can survive shorter periods of time during Canada’s summer.
Screwworm itself is endemic to South America and Caribbean countries. The United States eradicated New World screwworm in 1966, and North America eradicated it by the 2000s. But warmer temperatures and changing weather, fueled by climate change, are thought to be expanding the flies’ range.
The dispute over response also has a sharper edge inside U.S. politics and agencies.
The Trump administration has faced increasing criticism for cuts to a U.S. Agency for International Development program that monitored and helped prevent screwworm spread in Central America. according to an agriculture industry trade publication. Texas Agriculture Commissioner Sid Miller told NBC that USDA moved too slowly and relied on a partial solution that would take years.
In response to emailed questions, USDA denied that budget cuts caused screwworm’s entrance into the country. Agriculture Secretary Brooke Rollins has blamed the previous Biden administration. which left office nearly a year and a half ago. for past immigration and border policies that allowed the parasite’s spread. Rollins said USDA is investing in sterile fly production and releases.
Those sterile-fly efforts are part of how officials are trying to interrupt the parasite’s life cycle. American officials are working to expand the use of sterile male screwworm flies: radiation sterilizes male flies. which are then dispersed where screwworm flies are indigenous. Since female screwworm flies typically mate only once, laying unfertilized eggs gradually decreases the population.
Taken together. the sequence is clear: USDA found larvae in South Texas on June 3 and confirmed a second case on June 5. and Canada responded with a 21-day Texas-based entry restriction on livestock. The anger from Texas followed quickly—centered on whether Canada’s broader rule matches the scientific risk—and the debate over who missed earlier warning signs has already spilled into federal politics.
As of now, Canada says it will keep working with U.S. counterparts and adjust measures as developments unfold. Texas has declared a disaster and. alongside USDA. is focused on containing and eradicating screwworm in a limited area of South Texas—while the broader economic question hangs over the border: how long a temporary restriction can stay “temporary” when a parasite moves faster than bureaucracy.
Contributing: Mary Walrath-Holdridge.
Eduardo Cuevas is based in New York City. Reach him by email at emcuevas1@usatoday.com or on Signal at emcuevas.
Canada Texas livestock ban New World screwworm flesh-eating parasite Greg Abbott disaster declaration USDA screwworm cases Canadian Food Inspection Agency sterile male screwworm flies cattle industry $15.5 billion