The United States Department of Health and Human Services has confirmed the first travel-associated human cases of New World screwworm in the country. The Centers for Disease Control and Prevention was responsible for verifying the diagnosis on 4 August 2025. Experts specifically reviewed images of larvae from the wound of the patient.
The case involves a Maryland resident who recently traveled to El Salvador, although earlier industry reports mentioned Guatemala as the origin. Health officials have not clarified the discrepancy. Authorities emphasized that the infection was acquired abroad and that the risk of public transmission within the United States remains very low.
New World screwworms are a species of parasitic blowflies whose larvae or maggots eat the living tissue of warm-blooded animals. These maggots are obligate parasites because they need to feed on living tissues to survive. Feeding is aggressive and leads to severe tissue damage and open wounds. Moreover, without treatment, the case can be fatal.
Treatment involves meticulous and repeated removal of larvae from the affected wound, combined with thorough cleaning to prevent secondary infections. Physicians may prescribe antibiotics to reduce bacterial risks and ensure proper healing. Supportive medical care is often necessary, especially when infestations are extensive or tissue damage is severe.
Human cases are rare, but infestations in livestock and wildlife can be catastrophic. U.S. Cattle producers are particularly alarmed because the pest has been advancing northward from Central America into southern Mexico since 2023, raising concerns about potential spread into domestic herds that are already facing historically low population numbers.
The U.S. Department of Agriculture has warned that a screwworm outbreak could cost Texas approximately USD 1.8 billion. This massive economic cost would come from livestock deaths, increased labor costs, and medical expenses. Such a scenario would also significantly impact the national beef supply chain at a time when cattle numbers are at a 70-year low.
Note that trade restrictions have already been in place to minimize the risk of an outbreak. Following the confirmation of a case in Veracruz, Mexico, located nearly 370 miles south of the border, the Department of Agriculture ordered the closure of different livestock ports of entry. Imports were similarly halted in November 2024 and again in May 2025.
The United States typically imports more than one million cattle from Mexico every year. The restrictions have created rippling effects across feedlots, processors, and beef futures markets. Hence, producers fear that if New World screwworms cross the border, eradication would be difficult and costly, placing additional strain on the beef industry.
Authorities depend on producing and releasing sterile insects. This biological control strategy eradicated screwworms domestically during the 1960s. The method specifically involves releasing large numbers of sterilized male flies to outcompete fertile ones. However, current production capacity is insufficient to meet the scale of the present regional threat.
The only existing production facility is located in Panama. It is capable of releasing about 100 million sterile flies per week. Experts estimate that at least 500 million sterile flies are required weekly to force the parasite back south to the Darien Gap in Central America. The Department of Agriculture announced plans in June to construct a facility in Texas.
At present, the confirmed case is isolated, and authorities describe the threat as minimal. However, the economic implications of a wider outbreak are serious. Industry officials and state veterinarians have expressed concerns over communication gaps. Some reported learning of the human case through industry channels before receiving federal briefings.
FURTHER READINGS AND REFERENCES
- Garrison, C., Polansek, T., and Douglas, L. 25 August 2025. “Exclusive: U.S. Confirms Nation’s First Travel-Associated Human Screwworm Case Connected to Central American Outbreak.” Reuters. Available online
- United States Department of Agriculture. 15 August 2025. “USDA Announces Sweeping Plans to Protect the United States from New World Screwworm.” USDA Press Releases. United States Department of Agriculture. Available online
- USDA Animal and Plant Health Inspection Service. 20 August 2025. “New World Screwworm.” Animals. USDA Animal and Plant Health Inspection Service. Available online