Earlier this week, the Department of Health and Human Services (HHS) confirmed the first human case of a flesh-eating parasite in the U.S.
The patient, a Maryland resident, had recently returned from travel to El Salvador and was found to be infected with New World screwworm, an HHS spokesperson told ABC News.
It comes amid an outbreak of the parasite among livestock in Mexico and countries across Central America.
Here’s what you need to know about the infestation, including how it spreads, what the signs are and how it can be treated.
What is New World screwworm?
New World screwworm (NWS) is a species of parasitic fly that feeds on live tissue and can cause myiasis, which is an infestation of larvae, or maggots.
They can infest many types of animals, including livestock, pets, wildlife and, in rare instances, humans.
Cochliomyia hominivorax, the New World screw-worm fly, or screw-worm for short, is a species of parasitic fly that is well known for the way in which its larvae (maggots) eat the living tissue.
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“New World screwworm kind of gets its name because these are little parasites and, when they actually land on an open wound, they’re going to screw down into the wound — that’s how they burrow in — and actually consume tissue,” Lori Ferrins, associate professor of pharmaceutical sciences at Northeastern University, told ABC News.
Ferrins explained that a female NWS will find a living host, land in an open wound and lay somewhere between 200 and 300 eggs. After the eggs hatch, the maggots burrow further into the tissue and cause painful infestations.
NWS is not typically found in the U.S. and is present in countries in Central and South America as well as the Caribbean, according to the Centers for Disease Control and Prevention (CDC).
NWS infection can cause several symptoms including skin lesions that don’t heal or worsen over time, painful wounds or sores, bleeding from open sores, feeling or seeing maggots in sore or a bad odor from the site of the infestation, according to the CDC.
The maggots can also be found in the eyes, nose and mouth, the federal health agency said.
“The larvae of the New World screwworm are particularly nasty, and that’s why it has been given this name,” Dr. Shira Doron, chief infection control officer for Tufts Medicine Health System, told ABC News. “Here in the hospital, we may have a patient come in and, with a painful open wound, we may notice that there are larvae or maggots in it.”
How is it treated?
There is currently no drug-only cure but there are effective treatments for NWS infestation. If someone believes they may be infected or sees and feels maggots in a wound or anywhere else in the body, they should contact a health care provider immediately, according to the CDC.
A physician will have to remove the maggots, which may require surgery, the CDC says. The agency said patients should not try to remove or dispose of the maggots themselves.
“We want to physically remove those, kill them, and send them off to a special lab to see if we’re dealing with something from another country, which then implies the need for a more robust public health response to prevent it from becoming a widespread problem,” Doron said.
How to prevent infection
Doron said anyone traveling to parts of the world where NWS infestation is common should keep any open wounds covered and use an insect repellent approved by the EPA.
“Things like long sleeves, long pants, tucking your pants into your socks, all of the techniques that you’ve probably heard of to avoid insect bites, because there are so many health implications that are associated with a wide variety of insects,” she said.
In this undated file photo, cattle are shown on a road on Ometepe Island, Rivas State, Nicaragua.
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Ferrins said there are currently efforts to prevent the parasite from crossing into the U.S., including building a sterile fly production facility in Texas.
“There are steps we can take … to then control or eliminate the presence of [NWS}, just like we did in 1966,” she said. “And so the way that that was actually done was through breeding and dispersing sterilized male flies that actually will mate with the wild female fly.”
She went on, “Effectively, that just means that when the female screwworm fly goes on to kind of lay its eggs again, they don’t hatch. And so that effectively stops the life cycle.”
How concerned should we be?
Ferrins said the U.S. eradicated screwworm in 1966, and the country has been relatively free of the parasite aside from an outbreak in 2017 in the Florida Keys.
“The Florida Keys incident or infection period resulted only in infections in animals, so there was no human infection at that time,” she said. “So, it’s very rare to actually even have a human infection.”
Screwworm has not been detected in animals within the U.S., but the U.S. Department of Agriculture said in a press release earlier this month that NWS “is not only a threat to our ranching community — but it is a threat to our food supply and our national security.”
Ferrins added that the risk of infection is currently low in the U.S., so there is no cause for major concern.
“My advice to people would be: be on your guard but ultimately, there’s no active signs of infection here, locally acquired infection in the United States,” she said.
ABC News’ Youri Benadjaoud contributed to this report.
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