A second case of the flesh-eating New World screwworm has been confirmed in South Texas, intensifying concerns among agricultural officials and prompting Canada to suspend livestock imports from Texas as authorities mount an aggressive response to prevent the parasite from spreading deeper into the United States.
The U.S. Department of Agriculture announced Friday that the latest case was discovered in a one-month-old calf in Zavala County, about 5.6 miles from the state’s first confirmed case in six decades, which was identified earlier this week. The detections mark a significant setback in efforts to keep the pest from reestablishing itself in the United States after it was declared eradicated nationally in 1966.
The New World screwworm is not a worm but the larval stage of a parasitic fly. Female flies deposit eggs in open wounds or body openings of warm-blooded animals. Once hatched, the larvae feed on living tissue, creating severe wounds that can become fatal if left untreated. Livestock, wildlife, pets and, in rare cases, humans can be affected.
The discovery has triggered a broad response from federal and state officials, who have spent more than a year preparing for the possibility that the pest, which has spread northward through Central America and Mexico, would eventually cross into the United States.
“USDA has responded expediently with respect to this second detection, demonstrating our utmost preparedness. This second detection is within the established movement control zone and enhanced sterile insect dispersal area,” said Dudley Hoskins, USDA’s under secretary for marketing and regulatory programs.
“Many models projected this pest would reach the United States last year, but thanks to USDA’s phenomenal work and our cooperation with state, federal, and industry partners, we’ve held it off until now—when we are far more prepared to respond. USDA has not wasted any time in this fight, we have defeated New World screwworm before, and we will do it again.”
The latest detection remains inside a 20-kilometer control zone established after the first case was discovered near the border. Federal officials said numerous additional suspect samples collected in the area have tested negative.
Still, the development has raised concerns throughout North America’s livestock industry.
On Friday, the Canadian Food Inspection Agency announced temporary restrictions on livestock imports from Texas. Under the order, cattle, horses and other livestock that originated in Texas or were present in the state within 21 days before entering Canada will be denied entry.
Canadian officials emphasized that the parasite is unlikely to establish itself permanently because of the country’s colder climate but said precautionary measures were necessary during the summer months.
The United States and Canada maintain a substantial cross-border livestock trade network, with animals routinely transported for breeding, feeding and slaughter. Canadian authorities imported roughly 550,000 cattle from the United States last year, according to government figures.
The Texas outbreak has also prompted Gov. Greg Abbott to issue a disaster declaration covering Zavala and neighboring Uvalde County.
“I am issuing an updated statewide disaster declaration to make two things very clear,” Abbott said in a statement. “First, I authorize the use of all available resources of state government to respond to this disaster and reassign resources from across the state as needed to address NWS. Second, I am making all state personnel available to accelerate the movement of sterile flies into Texas and the construction of the new sterile screwworm production facility in Edinburg.”
Abbott warned Friday that the infestation is likely to expand during the coming months.
“This is likely to spread over the course of the summer,” he told reporters.
State officials have directed resources toward containment efforts while urging ranchers, veterinarians and pet owners to inspect animals daily for suspicious wounds, lesions or signs of infestation.
At the center of the eradication strategy is a technique that helped eliminate the pest from the United States decades ago: the mass release of sterile male flies.
USDA officials said aerial operations began June 4, with aircraft dispersing 2 million sterile screwworm flies twice each week over the affected region. Another 4 million sterile flies per week are being shipped into Texas for ground releases at strategically positioned sites surrounding the outbreak area.
The sterile males mate with wild females, which typically mate only once in their lifetimes. The resulting eggs do not hatch, gradually collapsing the pest population.
Federal officials have also deployed veterinary strike teams, mobile laboratory trailers and diagnostic specialists to South Texas. The National Veterinary Stockpile has moved treatment supplies into the state, while the Food and Drug Administration has issued emergency use authorizations for several screwworm treatment products.
The current outbreak follows months of mounting concern among livestock producers as cases advanced northward through Mexico. In response, USDA expanded surveillance programs, increased border monitoring and worked with authorities in Mexico and Central America to slow the insect’s progression.
Whether those efforts will be enough to prevent a wider outbreak remains uncertain. Some experts have questioned whether sterile-fly releases alone can keep pace with the parasite’s spread across a vast region characterized by abundant wildlife and livestock populations.
For now, officials say the public should remain vigilant but not alarmed.
USDA stressed that the nation’s food supply remains safe because screwworms do not infest meat, fruits, vegetables or other food products. Any infected animals would be identified during federal inspection processes and prevented from entering the food chain.
The larger concern, officials say, is protecting livestock herds and wildlife populations from a parasite capable of inflicting significant economic damage if allowed to gain a foothold.
“We have eradicated this pest before,” Abbott said, “and we will do it again.”
CLICK HERE for the official press release from the Canadian Food Inspection Agency.
