The first human case of the flesh-eating New World screwworm parasite in the United States has been confirmed, the Department of Health and Human Services (HHS) said Sunday.
The case, investigated by the Maryland Department of Health and the US Centers for Disease Control and Prevention (CDC), was verified by the CDC on August 4 and involved a patient who had returned from travel to El Salvador, HHS spokesperson Andrew G. Nixon said in an email to Reuters.
Earlier, Reuters reported that beef industry sources claimed the CDC had confirmed a case in Maryland in a person who had traveled from Guatemala. Nixon did not clarify the discrepancy. “The risk to public health in the United States from this introduction is very low,” he said.
No animal cases have been reported in the country this year. The conflicting accounts from government officials and industry sources are expected to unsettle cattle ranchers, beef producers, and livestock traders, who remain on alert as screwworm continues to spread north from Central America and southern Mexico.
The confirmation came just over a week after US Department of Agriculture (USDA) Secretary Brooke Rollins announced in Texas that a sterile fly facility would be built to help combat the pest. The USDA has estimated that a screwworm outbreak could cost Texas, the nation’s largest cattle-producing state, about $1.8 billion in livestock deaths, labor, and treatment costs.
According to a source who shared email contents with Reuters, an executive with the Beef Alliance informed livestock and beef sector representatives last week that the CDC had confirmed a human screwworm case in Maryland in a traveler from Guatemala.
Beth Thompson, South Dakota’s state veterinarian, told Reuters she was informed of a human case in Maryland within the last week by someone with direct knowledge. Thompson said the CDC deferred questions to Maryland during a call with state animal health officials. “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.”
Another source confirmed that state veterinarians learned of the Maryland case in a call with the CDC last week. A Maryland state government official also confirmed the case. The Maryland Department of Health did not immediately respond to requests for comment.
Screwworms are parasitic flies whose females lay eggs in wounds on warm-blooded animals. When the eggs hatch, hundreds of larvae burrow into living flesh, often killing their host if untreated. The burrowing resembles a screw entering wood, giving the parasite its name. Although human cases are rare, infestations can be fatal.
Treatment requires removing the larvae and disinfecting wounds, though most cases are survivable if treated early. According to the Beef Alliance emails, no further details about the Maryland patient were available due to privacy laws. The individual received treatment, and prevention measures were enacted in the state.
The emails also indicated that a livestock economist at Texas A&M University was asked to prepare a report for Rollins on the economic impacts of a border closure to Mexican cattle, which has been in place since November to block screwworm entry into the US.
The CDC was required to report the confirmed screwworm case to Maryland health officials and the state veterinarian, according to one of the emails, and 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 Alliance executive wrote.
