Maryland screwworm case has US officials bracing for return of an old foe

An adult New World screwworm fly. The species’ parasitic larvae can cause devastating outbreaks in livestock. Photograph: Denise Bonilla/AP

A patient in Maryland was diagnosed in August with New World screwworm, a parasitic fly, after traveling to El Salvador. Doctors and veterinarians say the case poses very low risks for human health in the US, but it comes after an increase of cases in South and Central America and the Caribbean in recent years. It also highlights the importance of international cooperation on research and prevention.

For decades, the fight against the screwworm was a success story of scientific innovation and collaboration with other countries. There were devastating outbreaks of the parasite in the US in the first half of the 20th century until an ambitious program pushed it south, all the way to Panama.