The first case of a New World screwworm (NWS) infestation in a human in the U.S. this year was confirmed and linked to a traveler who returned to Maryland from El Salvador.
The U.S. Department of Health and Human Services (HHS) confirmed the case, which was investigated by the Maryland Department of Health and the U.S. Centers for Disease Control and Prevention (CDC). The case was investigated on Aug. 4, but exact travel dates have not been reported.
As this is a human case, CDC is the lead response agency and is conducting an epidemiological assessment in coordination with local health authorities, according to USDA.
“In support of CDC’s activities and out of an abundance of caution, USDA initiated targeted surveillance for NWS within a 20-mile radius of the affected area, encompassing portions of the District of Columbia, Maryland, and Virginia,” USDA said in an Aug. 26 news release. “To date, all trap results have been negative for NWS.”
The case was first reported by Reuters on Aug. 24. An initial report said the traveler had returned from Guatemala.
HHS spokesman Andrew G. Nixon wrote in an email to Reuters that the risk to public health in the U.S. is low.
“This is the first human case of travel-associated New World screwworm myiasis (parasitic infestation of fly larvae) from an outbreak-affected country identified in the United States,” Nixon said.
Upon the news, National Cattlemen’s Beef Association CEO Colin Woodall said they do not see any elevated risks to the livestock industry at this time. “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,” Woodall said.
The U.S. has not confirmed any NWS cases in animals. The closest reported case was found in Veracruz, Mexico, in July, about 370 miles south of the U.S./Mexico border. The border remains closed to livestock imports.
Following the Reuters report of the confirmed NWS detection in a human, Ranchers-Cattlemen Action Legal Fund, USA (R-CALF) called for an investigation into the transparency of the case. The Reuters report said a handful of livestock industry groups were informed of the pest’s detection in mid-August, which was originally believed to have originated from Guatemala.
“If a human case of New World Screwworm was confirmed on or about Aug. 20, and if that fact was secretly disseminated to only a select group of industry insiders, but not simultaneously shared with all organizations representing independent livestock producers, or even with state veterinarians instrumental in disease and pest surveillance, then we ask for a full investigation of this incident and the establishment of a New World Screwworm task force comprised of representatives of each sector of America’s livestock industries to ensure future transparency and the proper allocation of resources to protect America from this devastating pest,” said R-CALF CEO Bill Bullard.
Cattle markets reacted unfavorably to the news on Monday morning, with feeder cattle futures sent lower. In May, a false detection of NWS in the U.S. caused a temporary market sell-off.
NWS details
The USDA estimates a screwworm outbreak could threaten over $100 billion in U.S. economic activity tied to the cattle and livestock industry.
According to the CDC, NWS is endemic in South America and the Caribbean. In 2023, NWS detections in Panama rapidly increased from an average of 25 cases per year to more than 6,500 cases in one year, according to USDA’s Animal and Plant Health Inspection Service. Since then, NWS has been found in Costa Rica, Nicaragua, Honduras, Guatemala, Belize, El Salvador and Mexico.
Although cases are rare, several reports of NWS have been detected in humans in the U.S., all linked to travel in endemic countries.
There are currently no drugs approved by the Food and Drug Administration (FDA) for NWS treatment. The only way to treat NWS is to physically remove the larvae from the infested tissue, CDC said.
On Aug. 19, HHS authorized the emergency use of animal drugs to treat or prevent NWS infestations only in animals. Through an emergency declaration, the FDA can “can authorize the flexible, faster use of certain animal drug products that may be approved for other purposes, or available in other countries, but not formally approved for NWS in the U.S.”
In mid-August, USDA announced it was investing $850 million into NWS detection and prevention efforts. Among the investments is a $750 million facility in Edinburg, TX, that will produce sterile screwworm flies so the population will eventually die out. The facility will be the first in the U.S. and is expected to take at least a year to complete. In the meantime, USDA is investing $100 million in technology to assist with U.S. response efforts.
In addition to the production facility, there is currently a dispersal facility in the works at Moore Air Base in Edinburg. The $8.5-million-facility will take larvae produced in Panama or Mexico and distribute hatched sterile flies to infestation sites. — Anna Miller Fortozo, WLJ managing editor
