What is New World screwworm? Travel-telated flesh-eating parasite found in US

Dubai: A Maryland resident who had traveled to El Salvador has been diagnosed with New World screwworm, a flesh-eating parasite rarely seen in humans.

US officials confirmed the case, saying the individual has since recovered and that there is no risk of transmission to others, according to CNN.

A spokesperson for the Maryland Department of Healthtold news agencies that the Maryland resident has recovered from the infection and that “there is no indication of transmission to any other individuals or animals.”

An outbreak of New World screwworms — the larval form of a type of fly that’s known to nest in the wounds of warm-blooded animals and slowly eat them alive — has been spreading across Central America since early 2023, with infestations recorded in Belize, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, Nicaragua and Panama.

The fly reached southern Mexico late last year, sparking concern among US agricultural industry officials and triggering closures of border-area cattle, horse and bison trading ports this year.

What exactly is the New World screwworm?

It’s the larval form of a blowfly that lays its eggs in open wounds or body openings such as the eyes, ears, nose, or mouth. The eggs hatch into flesh-eating maggots that burrow deeper into living tissue. The parasite is notorious in livestock but rarely infects humans. Its scientific name roughly translates to “man eater.”

Why is it called a “screwworm”?

The larvae grow up to two-thirds of an inch long and twist into the flesh in a screw-like fashion, giving them their name.

How do people get infected?

Infections occur when flies lay eggs in an open wound or sore. Travelers are more at risk if they spend time in areas with livestock, sleep outdoors, or have untreated cuts or skin injuries.

What are the symptoms?

Patients may develop painful wounds that don’t heal, sometimes with a foul smell. A clear warning sign is the presence of maggots around an open sore.

How is it treated?

Doctors must physically remove the larvae, sometimes through surgery. Health officials warn people not to attempt removing the maggots themselves.  

How big a threat is this to the US?

Health officials say the public risk is very low, as the parasite doesn’t spread from person to person. But the case highlights a growing concern for ranchers: screwworm infestations have been spreading northward through Central America and Mexico.

Why does it matter for livestock and agriculture?

The screwworm devastated US cattle industries until it was eradicated in the 1960s and 1970s through an aggressive program that released sterilized male flies from airplanes.

The pest kills animals by infesting wounds and slowly eating them alive, threatening food supply chains, according to the Associated Press news agency.

Could screwworm return to the United States?

Scientists say it’s possible, especially along the Texas-Mexico border, where livestock trade is heavy. The US Department of Agriculture is now building a new facility in Texas capable of producing 300 million sterile flies a week to prevent a reintroduction

Bottom line?

While the Maryland case is the first US human infection tied to travel from an outbreak zone, officials stress that the risk to people remains low. The greater danger lies in protecting America’s livestock industry from a parasite once considered one of its most destructive pests.  

“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,” Health and Human Services spokesperson Andrew Nixon said, according to CNN.

“Currently, the risk to public health in the United States from this introduction is very low.”

-- With inputs from AP