Beth Thompson, South Dakota's state veterinarian, told Reuters on Sunday that she was notified of the case within the last week by a person with direct knowledge of the Maryland case.
A second source, who asked not to be identified, said they had seen emails sent by an executive of the industry group Beef Alliance on August 20 to about two dozen people in the livestock and beef sectors, informing them that the U.S. Centers for Disease Control and Prevention had confirmed a human case of screwworm in Maryland in a person who had traveled to the U.S. from Guatemala.
State veterinarians learned about the human case in Maryland during a call last week with the CDC, according to one source. A Maryland state government official also confirmed the case.
“We found out via other routes and then had to go to CDC to tell us what was going on,” she said. “They weren’t forthcoming at all. They turned it back over to the state to confirm anything that had happened or what had been found in this traveler.”
The confirmed case comes just over a week after U.S. Department of Agriculture Secretary Brooke Rollins and other government officials traveled to Texas to announce plans to build a sterile fly facility there as part of efforts to combat the pest.
Screwworms can be devastating in cattle and wildlife, and rarely infest humans, though an infestation in either an animal or a person can be fatal.
The maggots' feeding is similar to a screw being driven into wood, giving the pests their name.
Treatment is onerous, and involves removing hundreds of larvae and thoroughly disinfecting wounds. But infestations are typically survivable if treated early enough.
The August 20 emails from the Beef Alliance executive, whose content was shared with Reuters, said the positive human case of New World screwworm in Maryland had been confirmed that day.
A follow-up email from the same group said that due to patient privacy laws, there were no other details available. The person was treated and prevention measures were implemented in the state, the email said.
The CDC was required to report the positive New World screwworm case to both Maryland health officials and the Maryland state veterinarian, one of the emails said, adding that the CDC also notified other agriculture stakeholders.
"We remain hopeful that, since awareness is currently limited to industry representatives and state veterinarians, the likelihood of a positive case being leaked is low, minimizing market impact," the beef industry executive wrote.
The case and the lack of transparency around it could also present a political challenge for Rollins, who pledged repeatedly to keep screwworm out of the country. The USDA has set traps and sent mounted officers along the border, but it has faced criticism from some cattle producers and market analysts for not acting faster to pursue increased fly production.
Rollins first announced plans for a sterile fly facility at Moore Air Force Base in Edinburg, Texas - near where a production facility to combat screwworm operated during the last major outbreak 50 years ago - in June, saying that the facility would take two to three years to come online.
Mexico has also taken efforts to limit the spread of the pest, which can kill livestock within weeks if not treated. The Mexican government said in July that it started to build a $51 million sterile fly production facility in the country's south.
The sole operating plant is in Panama City and can produce a maximum of 100 million sterile screwworm flies each week. The USDA has estimated that 500 million flies would need to be released weekly to push the fly back to the Darien Gap, the stretch of rainforest between Panama and Colombia.
Screwworms have been traveling north through Mexico from Central America since 2023. They are endemic in Cuba, Haiti, the Dominican Republic and countries in South America, according to the USDA.
