US to Deploy Sterile Flies and Sniffer Dogs to Combat First Screwworm Outbreak in Decades

Federal agriculture and health authorities have unveiled a strategy to tackle a flesh-eating parasite detected in the United States for the first time since 1966. The initiative to prevent the establishment of the New World Screwworm relies heavily on the release of hundreds of millions of genetically modified sterile flies. However, experts caution that the current production capacity of sterile insects is insufficient to immediately suppress the expanding population. Supplementary tactics involve creating a containment perimeter around the initial infection site near the southern border and employing trained sniffer dogs to locate the pests.

While the risk to humans remains minimal, cattle producers are concerned that an uncontrolled outbreak could severely disrupt beef markets. Screwworms are parasitic flies that deposit their eggs in the open wounds and mucous membranes of warm-blooded hosts, including livestock and people. Upon hatching, the larvae use their sharp mouthparts to burrow into living tissue, which can prove fatal to the host if not treated.

On Wednesday, US officials confirmed the first case in 60 years, identifying larvae in the umbilical region of a three-week-old calf. The discovery occurred in La Pryor, Texas, located approximately 30 miles (48km) from the Mexican border. In response, the US Department of Agriculture (USDA) has established a 20km-wide "control zone," implementing strict quarantines, movement restrictions, and enhanced surveillance within the area.

Although screwworm larvae develop into flies capable of short-distance flight, long-range spread is primarily facilitated by human transport. Since 1966, when travelers inadvertently introduced the pest, the US has seen isolated cases but no major outbreaks. For much of the last six decades, officials in the US and Latin America have struggled to fully eradicate the problem.

A primary defense mechanism is the Sterile Insect Technique, which involves releasing vast numbers of sterile flies. Because female screwworms mate only once, any eggs they lay after mating with sterile males remain unfertilized and fail to hatch. This method, long used to manage populations of fruit flies and mosquitoes, involves raising flies in controlled environments, exposing them to radiation to induce sterility, and then releasing them into the wild.

Despite the effectiveness of this technique, US officials state they need to produce up to 600 million sterile screwworms weekly to effectively combat the current outbreak. Currently, facilities in the US and Mexico can only generate approximately 100 million per week.

US Secretary of Agriculture Brooke Rollins stated on Thursday that since the infected calf was identified, officials have distributed four million sterile flies via ground transport. Additionally, since February, four million more have been released weekly by air. "There is no reason to believe that this incursion will result in any sort of establishment of the pests," Rollins told reporters.

Nevertheless, critics, including Texas cattle farmers, argue the response is inadequate. Some have accused the Trump administration of downplaying the severity of the issue. The last time the US faced a significant threat was in the 1970s, though no screwworms were ever found inside the country during that period. At that time, the deployment of 500 to 700 million sterile flies weekly across Central America successfully pushed the pests south of the Darien Gap, a densely forested border region between Panama and Colombia, according to Sonja Swiger, an entomologist at Texas A&M University.

In recent years, however, the pest has moved northward. Panama reported a surge in cases in 2022, followed by increases across Central America. By 2024, screwworms had appeared in Mexico and were advancing toward the US border. This latest outbreak has already resulted in 2,070 confirmed cases of screwworms in

Source: BBC News Generated at: 2026-06-05 00:56:42 UTC