A U.S. traveler returning from El Salvador has been diagnosed with New World screwworm, marking the country’s first confirmed human case in decades.
At a Glance
- HHS confirmed a U.S. human case of New World screwworm
- Infection linked to travel from El Salvador, amid outbreak
- Case diagnosed remotely by CDC and Maryland officials on Aug. 4
- Screwworm eradicated in U.S. in 1982 through bio-control programs
- Parasite larvae consume living tissue, requiring urgent care
A Fly from the Tropics
The Department of Health and Human Services (HHS) confirmed on August 4, 2025, that a U.S. resident returning from El Salvador was infected with New World screwworm. The parasite, Cochliomyia hominivorax, is known for laying eggs in living tissue, where the larvae feed and grow, causing flesh to decay from the inside out.
Officials from the Centers for Disease Control and Prevention (CDC) worked with the Maryland Department of Health to identify the parasite through telediagnosis. The infected individual, whose identity has not been disclosed, had recently traveled to El Salvador, a country currently experiencing an outbreak of the parasite.
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This detection marks the first confirmed human case in the U.S. since the eradication of the parasite through decades-long government sterilization programs. The screwworm had been eliminated domestically by 1982, thanks to a massive sterile-insect release campaign in partnership with Mexico.
Parasite With a Nasty Bite
The New World screwworm primarily affects livestock, but in humans, infestations can be severe. Female flies lay eggs in open wounds or mucous membranes. Once hatched, larvae consume healthy tissue, expanding lesions and increasing the risk of secondary infections. In untreated cases, myiasis can lead to systemic illness or death.
The patient was diagnosed following the remote review of wound imagery by entomologists and infectious disease specialists. Immediate treatment included surgical removal of the larvae and administration of antiparasitic medications. Health officials report the patient is recovering and no secondary infections have been identified.
Risk of Reintroduction?
Although the U.S. has not seen endemic screwworm cases in decades, global travel remains a route of re-entry. The CDC has reminded clinicians to remain vigilant for tropical parasites in patients returning from endemic regions. El Salvador, the source of this case, reported an uptick in screwworm cases in livestock and humans earlier this year, triggering concern from both local and international health bodies.
The USDA’s Animal and Plant Health Inspection Service continues to monitor livestock populations for signs of infestation. So far, no additional U.S. human or animal cases have been confirmed. The agency has not announced any changes to inspection protocols at airports or ports of entry but is reportedly reviewing procedures in light of the case.
Sources
The Hill
CDC
WHO
USDA APHIS
Nature Microbiology
