First Human Case of New World Screwworm in the U.S.

On Sunday, the U.S. Department of Health and Human Services announced the first reported human case of a New World screwworm linked to travel, which is a meat-eating parasite. This outbreak has raised concerns across several sectors.

The incident was investigated by the Maryland Department of Health alongside the U.S. Centers for Disease Control and Prevention (CDC). The CDC confirmed the case on August 4, involving a traveler who returned to the U.S. from El Salvador, according to HHS spokesman Andrew G. Nixon.

Prior to this, there were reports that cases of New World screwworms were confirmed in Maryland, with individuals having traveled from Guatemala to the U.S., as indicated by a source within the beef industry.

Nixon did not clarify any inconsistencies regarding the origins of the human cases. He did, however, state that “the risk to public health in the United States from this referral is very low.”

As of now, the government has not confirmed any animal cases this year. However, conflicting information from government and industry sources about human cases could provoke concerns in industries already jittery about potential outbreaks impacting cattle ranchers and beef producers.

The confirmation regarding screwworms came shortly after the USDA’s Brook Rollins Bureau announced plans to create an infertile fly facility in Texas, part of an initiative to combat these pests. Texas is the nation’s largest cattle producer, and the potential economic implications are significant.

Executives from the Beef Alliance sent an email to several stakeholders in the livestock sector, informing them of the confirmed Maryland cases and advising discretion regarding the details shared.

South Dakota state veterinarian Beth Thompson mentioned that she learned about the human case in Maryland from a call with state animal health officials. “They weren’t forthcoming,” she shared, reflecting on how the information was handled.

Another source noted that the Maryland government confirmed the case during a call with the CDC last week.

A spokesperson from the Maryland Department of Health has not yet responded to requests for comments.

Understanding Screwworms

Screwworms are parasitic flies that lay their eggs on open wounds of warm-blooded animals. Once the eggs hatch, the larvae can invade healthy tissue, causing severe harm and even death if treatment is not administered promptly.

The process of feeding resembles the action of a screw being driven into wood, which is how they got their name. Though mostly harmful to livestock and wildlife, human infections are rare but can be fatal.

Treatment involves painstaking removal of the larvae and disinfecting the wounds. However, if addressed quickly, the prognosis can improve significantly.

An email from the Beef Alliance mentioned that no further details could be shared regarding the human cases due to patient privacy regulations; however, precautions were implemented in state initiatives following the treatment of the affected individual.

Livestock economists from Texas A&M University were engaged to prepare a report focusing on the economic repercussions due to border closures affecting Mexican cattle, a measure implemented to prevent the introduction of screwworms into the U.S.

The CDC is required to inform Maryland health officials and veterinarians about confirmed cases, and additional notifications have been sent to other agricultural stakeholders.

“As awareness is mostly limited to industry representatives, we hope that the chances of any cases leaking out will be minimal and that market impacts remain contained,” wrote a beef industry executive.

Representatives from the Beef Alliance have not commented on the situation thus far.

Beef Industry Implications

With U.S. cattle herds at their smallest in seventy years, prices are experiencing unprecedented highs, leaving many in the livestock and beef sectors anxious about the possible spread of screwworms.

The obscurity surrounding human cases may pose a political challenge for officials like Rollins. Although the USDA set traps and deployed resources along the border to curb the problem, some cattle producers and market analysts are criticizing the pace of these efforts.

Plans are underway for a sterile fly facility at Moore Air Force Base in Edinburg, Texas, aimed at managing screwworms more effectively. Initially announced in June, it may take two to three years before the facility becomes operational. In the meantime, Mexico has also begun constructing a sterile fly production facility.

The only operational facility is in Panama City, with a weekly output capable of producing up to 100 million sterile flies. The USDA estimates that around 500 million flies would need to be released weekly to combat the issue effectively.

Screwworms have been migrating north from Central America and Mexico since 2023, with Mexico reporting incidents close to the U.S. border. Consequently, the USDA has taken steps to halt livestock trade via specific ports, a significant measure since the U.S. imports over a million cattle yearly for beef production.

In the 1960s, a similar screwworm crisis was eradicated in the U.S. with the strategic release of sterile male flies that only produced infertile eggs when mating with wild females.