New World Screwworm Threatens U.S. Livestock as Parasite Spreads Toward Southern Border
Why It Matters
A flesh-eating parasite is advancing toward the United States, threatening to drive beef prices even higher and disrupt livestock markets that are already strained. Southern states — and agricultural economies as far north as Missouri — face serious risk if the New World screwworm crosses the U.S.-Mexico border, where multiple confirmed cases have already been detected within 100 miles of American soil.
Beef prices have hit record highs, and food affordability concerns are already placing pressure on household budgets. A domestic screwworm outbreak could compound those pressures significantly.
What Happened
The New World screwworm — a parasite eradicated from the United States in the 1960s — has been spreading through Mexico and Central America and is now approaching the southern U.S. border. The fly deposits eggs in wounds or body openings of living animals; the larvae then burrow into living tissue, causing severe damage and, in some cases, death. The parasite can affect livestock, pets, wildlife, and in rare instances, humans.
Federal officials have already banned imports of live cattle from Mexico in response to the threat, a move that has tightened an already constrained domestic beef supply. State and federal agencies have simultaneously rolled out new monitoring, testing, and quarantine protocols to prepare for a potential incursion.
Texas Agriculture Commissioner Sid Miller said he believes a U.S. infestation is inevitable. “We’re going to get infested,” he said in remarks attributed to him publicly. “There’s no doubt about it.”
By the Numbers
- $6.90 per pound — the current average retail price of ground beef, according to federal data
- 77% — the increase in ground beef prices since January 2020, when the average was $3.89 per pound
- 75 years — the period over which U.S. cattle herd sizes have fallen to their current low, according to the American Farm Bureau Federation
- $750 million — the cost of a new sterile fly production facility under construction in Edinburg, Texas, expected to produce up to 300 million sterile flies per week upon opening next year
- 30 tests — the number New Mexico has already conducted through county extension offices, all of which returned negative results
The Federal Response
The U.S. Department of Agriculture’s primary countermeasure relies on releasing sterile male flies into infested areas. Because female screwworm flies mate only once, mating with a sterile male results in unfertilized eggs, gradually collapsing the local population. The agency has invested in sterile fly production infrastructure in Texas, Mexico, and Panama.
The USDA has also granted emergency authorization for several medications — including ivermectin — for prevention and treatment of screwworm infestation in livestock. However, Dr. Samantha Holeck, state veterinarian with the New Mexico Livestock Board, cautioned ranchers against rushing to preventive treatment. “We need to be very judicious about how we use them, because we don’t want to create resistance,” she said.
Miller expressed skepticism that the planned sterile fly facilities would produce enough volume to stop an infestation. He noted the USDA has already distributed test kits to ranchers, veterinarians, and wildlife personnel along the Rio Grande.
Market and Agricultural Impact
The ban on live Mexican cattle imports has already disrupted supply chains, as Mexican cattle traditionally occupy American pastures and feedlots ahead of slaughter. Texas A&M livestock marketing specialist David Anderson said producers appear well-positioned to fight an infestation but warned that beef prices are unlikely to decline anytime soon. Rebuilding herd sizes takes years, and demand remains strong despite constrained supply.
Ranchers are being advised to monitor newborn calves closely, particularly around exposed umbilical cords, and to reconsider routine branding and tagging operations in the event of an outbreak, as those wounds can serve as entry points for larvae.
What’s Next
The Edinburg, Texas, sterile fly facility is expected to begin operations next year. New Mexico has established a centralized information hub through its Department of Agriculture in coordination with other agencies, and test kits have been distributed to every county extension office in the state.
Holeck emphasized that the last major screwworm infestation required more than a decade of coordinated binational effort to eliminate. “It’s not going to be a quick fix,” she said. “It’s going to require everybody to work together.”
Federal and state officials are treating a domestic infestation not as a possibility to be avoided, but as a contingency to be managed — with re-eradication the stated long-term goal.