A human case of flesh-eating screwworm was detected in the U.S. related to the the latest outbreak of the parasite in Central America, according to officials.
The patient had recently returned to Maryland after traveling to El Salvador, Andrew G. Nixon, a spokesperson for the U.S. Department of Health and Human Services, told Reuters in an email.
On Aug. 4, the Maryland Department of Health and the Centers for Disease Control and Prevention confirmed the parasite as a New World screwworm, but said it is travel-related.
“The risk to public health in the United States from this introduction is very low,” Nixon said.
While the chance of people contracting the parasite in the U.S. is low, here’s what to know about the New World Screwworm.
Larvae of the screwworm fly, collected from infected cows, are observed at the COPEG sterile fly production plant, which fights the spread of the cattle screwworm, in Pacora, Panama, June 11, 2025.
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What is a New World Screwworm?
The larva of the New World Screwworm flies feed on living tissue, and mainly impacts animals and livestock. But humans can also become infested by the larva, according to the CDC.
The fly was eradicated in the U.S. in the 1960s and in Mexico in the 1970s. But Panama, Costa Rica, Nicaragua and Honduras have recently documented cases despite the parasite also being eradicated in Central America in the early 2000s.
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Who will be impacted most by the New World Screwworm?
Travel-related cases of screwworm pose a low threat to the public health of the U.S., and the government has not confirmed any cases of screwworm infesting animals in the U.S. in 2025.
The case, however, will likely shake the cattle ranchers, beef producers and livestock traders who were already put on alert about potential screwworm infestations, according to Reuters.
The parasite has since moved into southern Mexico from Central America, causing concern for potential infestation if the fly continues to move northward.
An outbreak in the U.S. would impact the cattle in the country and raise already record-high beef prices.
A sample of screwworms collected in the morning are displayed at the veterinary clinic as the Mexican government and ranchers struggle to control the spread of this flesh-eating pest, in Tapachula, Chiapas state, Mexico July 4, 2025.
Combatting the screwworm
The U.S. Department of Agriculture will build a facility in Texas, the largest cattle-producing state, that will produce sterile flies to try and keep the flies’ population from growing.
The department will spend up to $750 million on the facility, according to Reuters.
Texas ranchers are anticipating the return of the parasite for the first time in decades.
How was the screwworm eradicated before?
In the 20th century, the U.S. eliminated the screwworm by flying planes over hotspots and dropping boxes of the sterile flies in hotpots, according to Reuters.
Contributing: Reuters
Julia is a trending reporter for USA TODAY. Connect with her on LinkedIn, X, Instagram and TikTok: @juliamariegz, or email her at jgomez@gannett.com
This article originally appeared on USA TODAY: New World Screwworm case in human detected in US. What to know.
