US Confirms First NWS Human Case

REDFIELD, Iowa (DTN) -- The first case of New World screwworm (NWS) was confirmed in a human in Maryland by the Centers for Disease Control (CDC) in coordination with the Maryland Department of Health.

A report from the director of communications for the Department of Health and Human Services said the case was in a patient who returned to the U.S. from travel to El Salvador and was confirmed by CDC through telediagnosis on Aug. 4, 2025. He said the risk to public health in the U.S. from this introduction is very low. The health status of the patient was not disclosed.

LIVESTOCK GROUPS SPEAK UP

The concern among livestock groups about the threat of NWS to the U.S. cattle herd continues, as U.S. Secretary of Agriculture Brooke Rollins recently announced construction of a $750 million facility to produce sterile NWS flies to help fight off the pest.

NCBA CEO Colin Woodall said: "NCBA is aware of the New World screwworm case detected in a person traveling from abroad into Maryland. The case was quickly identified and handled by the CDC in accordance to their protocols."

NWS larvae only feed on live tissue of warm-blooded animals. It is more common in livestock and other animals and rarely found in humans; thus, humans are not considered to be at high risk. NWS is also not a contagious disease, according to Cody Egnor, veterinary medical officer with USDA's Animal & Plant Inspection Service.

"Female flies deposit eggs in wounds and some mucus membranes," he said. "Humans could have eggs laid in wounds if they are not covered and are in contact with the flies."

Untreated animals infested with NWS through a wound can die within two weeks without treatment, and newborn animals are very likely to die if not protected in areas where the pest is found in the environment.

"Based on what has been shared with state animal health officials, we do not see any elevated risk to the livestock industry at this time," Woodall said. "We appreciate the diligence of human health authorities. This case was quickly addressed thanks to existing protocols, and we are thankful for the ongoing coordination between the CDC, state departments of health, state animal health officials, and USDA."

TRANSPARENCY CONCERNS BROUGHT FORWARD

Bill Bullard, R-CALF USA CEO, is not only concerned about the NWS human case, but also about the sharing of information regarding the case. Though the case was confirmed by the CDC on Aug. 4, no information was released to the public until Reuters news agency reported on it over the weekend.

"We are deeply concerned that if the publicly disseminated Reuters report is accurate, including its implication that only select industry participants were timely informed of the detection of this devastating pest in the United States, then our governmental system is fundamentally broken," he said in a news release. "Independent U.S. livestock producers rely exclusively on the USDA to protect the health and safety of their livestock herds against the introduction of foreign pests and to protect the integrity of their U.S. livestock markets by preventing manipulation."

Bullard further stated that the information about the NWS human case should be shared transparently with all industry participants, including producers.

Food and Drug Administration Commissioner Marty Makary stated last week following the approval of certain livestock drugs to be used to fight NWS that aren't labeled for use against an infestation: "Our priority is to safeguard both animal health and the nation's food supply. FDA is acting swiftly and responsibly to help ensure we have the necessary tools to prevent and control New World screwworm, minimizing risks to agriculture and public health."

SHIFT IN MARKETS

DTN Livestock Market Analyst ShayLe Stewart said that the cattle complex opened to a grim reality Monday morning after an exceptionally strong week last week.

"Last week, fed cash cattle prices jumped $2 to $5 higher, the CME feeder cattle index reached a new all-time high of $350.18, and both the live cattle and feeder cattle contracts achieved new contracts highs as well," Stewart said. "But over the weekend, news broke from the CDC that a positive case of New World screwworm had been detected in a person traveling abroad into Maryland, which consequently drove prices sharply lower at Monday's start."

Stewart continued that Friday's USDA Cattle on Feed report also didn't help matters, as the report didn't show as steep of a year-over-year regression in placements as most analysts assumed it would.

"But more than anything, Monday's weakness is being driven by the news of the positive NWS case, and it's likely that an unsettled, uneasy tone lingers throughout the market for multiple days," she added.

For more analysis on how the human NWS case could affect livestock markets, see Sort and Cull: "New World Screwworm Wasn't on the Cattle Market's Bingo Card" here: https://www.dtnpf.com/….

Jennifer Carrico can be reached at jennifer.carrico@dtn.com

Follow her on social platform X @JennCattleGal.

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