Canada Halts Texas Livestock Imports Over New World Screwworm Resurgence
Canada announced a temporary ban on livestock imports from Texas on June 5, citing the re-emergence of the New World screwworm — a parasitic fly that feeds on living tissue — in the United States for the first time since it was eradicated in 1966.
The Canadian Food Inspection Agency (CFIA) said the restriction applies to animals, including horses, that originated from or were present in Texas within 21 days before entry into Canada. The agency noted that the parasite is not currently present in Canada but acknowledged that warmer summer temperatures could allow the flies to survive for short periods.
The move came after the U.S. Department of Agriculture (USDA) confirmed two cases of screwworm infestation in calves in South Texas — the first domestic cases since the pest was wiped out from North America by the early 2000s. The initial discovery, made June 3, involved a three-week-old calf with larvae in its umbilical area; a second case was found June 5 in a one-month-old calf about five miles away.
New World screwworm flies, roughly the size of a housefly, lay eggs in open wounds or body openings of warm-blooded animals. Once hatched, the larvae burrow into the flesh, feeding on living tissue and creating painful, foul-smelling wounds that can lead to severe secondary infections or death, according to the U.S. Centers for Disease Control and Prevention.
Texas Gov. Greg Abbott declared a state of disaster on June 5, calling the parasite an “imminent threat” to the state’s $15.5 billion cattle industry. But his spokesman, Andrew Mahaleris, pushed back on Canada’s response, saying in a statement that “Canada's broad restriction on Texas livestock is an overreaction that is more political than science-based.” Mahaleris stressed that the pest affects live animals, not inspected beef, and that Texas and the USDA are moving quickly to contain the outbreak to a limited area.
Canada had already imposed a similar ban on most livestock from Mexico, and the U.S. closed southern border ports to livestock trade with Mexico in July 2024. The United States is Canada’s largest agricultural trade partner, supplying more than $3 billion in live animals and animal products in 2024, according to USDA data. While the exact share from Texas isn’t specified, the state is the nation’s top producer of beef and cattle.
The screwworm’s return has also ignited political blame. Agriculture industry reports have noted that cuts to a USAID program monitoring screwworm in Central America — made by Elon Musk’s Department of Government Efficiency under the Trump administration — may have weakened prevention efforts. Texas Agriculture Commissioner Sid Miller told NBC that the USDA moved too slowly and relied on a partial solution that would take years.
In response, the USDA denied that budget cuts caused the parasite’s entry into the U.S., and Agriculture Secretary Brooke Rollins instead blamed the Biden administration’s immigration and border policies for allowing the spread. She emphasized that the USDA is now investing in sterile fly production and releases — a technique that uses radiation-sterilized male flies to mate with females, which then lay unfertilized eggs, gradually reducing the population.
Originally endemic to South America and the Caribbean, New World screwworm was eradicated from the U.S. in 1966 and from all of North America by the 2000s. Scientists believe climate change, with warmer temperatures and shifting weather patterns, is expanding the flies’ range northward, raising risks for other southern U.S. states with warm, humid climates. Canadian officials noted that while the parasite cannot survive Canada’s colder winters, it could persist during the summer months.
Contributing: Mary Walrath-Holdridge, USA TODAY
Eduardo Cuevas is based in New York City. Reach him by email at [email protected] or on Signal at emcuevas.01.
This article originally appeared on USA TODAY: Canada bans Texas livestock over spread of flesh-eating parasite