New World Screwworms Have Returned to Central America

New World screwworm (NWS) infestations have continued to be reported in the Region of the Americas this year, and the U.S. government is concerned that NWS maggots may return after five decades.

According to a notice issued by the U.S. Department of Agriculture on November 1, 2024, NWS is endemic in Cuba, Haiti, the Dominican Republic, and countries in South America.

By October 26, 2024, Panama had reported 20,417 positive NWS cases, Costa Rica had 7,718, and Nicaragua had 4,384 cases in 2024.

In 2023, more than 6,500 NWS cases were detected in Panama.

The USDA says it eradicated NWS from the United States in 1966 using the sterile insect technique, in which sterile flies are released in the wild. Further, the USDA says there is a constant risk of NWS reintroduction in the United States.

In mid-October 2024, the U.S. CDC Clinician Outreach and Communication Activity call highlighted concerns about a potential northward spread of NWSs.

The cornerstone of a collaboration between the Panama-United States Commission for the Eradication and Prevention of Screwworms is releasing sterile male screwworm flies in the Darian Province of eastern Panama to create a biological barrier. This effort is scheduled to continue for an extended period.

As of November 4, 2024, there are no NWS vaccines available.