Maryland resident is diagnosed with New World screwworm. What to know
about the parasite
[August 26, 2025]
By MIKE STOBBE
NEW YORK (AP) — A Maryland resident who traveled to El Salvador has been
diagnosed with New World screwworm — the first reported U.S. case tied
to travel to a country with a current outbreak.
The Centers for Disease Control and Prevention confirmed the diagnosis
on Aug. 4. Federal health officials acknowledged the infection in an
emailed statement Monday.
The person has recovered, and investigators found no transmission to any
other people or animals, Maryland health officials said.
New World screwworm is a fly that lays its eggs in open wounds and body
openings. The parasite is typically found in South America and the
Caribbean.
It is rare in humans but has been a concern to ranchers, as cattle
infestations have been moving northward through Central America and
Mexico. The CDC is working with the U.S. Agriculture Department to
prevent further spread, officials said.
The pest was a recurring problem for the American cattle industry for
decades, with Florida and Texas known as hot spots, until the U.S.
largely eradicated it in the 1960s and 1970s.
Given that history, the Maryland case is likely not first time an
American has ever been diagnosed with it, said Max Scott, a North
Carolina State University research who has studied it. But this appears
to be the first case in a U.S. resident in quite a while, he said.
Here's more to know:
What is New World screwworm?
The name refers to a blue-green blowfly that became somewhat infamous
after infestations were reported in the 19th century at the Devil’s
Island penal colony off the coast of South America.
Its Latin species name roughly translates to “man eater,” Scott said.
Female flies lay eggs in an open wound or in the nose, eyes or mouth of
an animal or person, which quickly grow into larvae that eat the flesh.
The screwworm part of the name comes from those maggots, which can get
up to two-thirds of an inch long and look like they are screwing
themselves into the flesh.
“It’s a nasty parasite,” Scott said.
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An adult New World screwworm fly sits at rest in this undated photo.
(Denise Bonilla/U.S. Department of Agriculture via AP)
 What are the risks and symptoms
for people?
The larvae do not spread from person to person, and they pose a very
low overall risk to the public, U.S. health officials said.
According to the CDC, people are at greater risk if
they travel to areas with animal infestations and spend time among
livestock, sleep outdoors and have an open wound.
Symptoms can also include painful, unexplained wounds or sores that
do not heal. One telltale sign is seeing maggots around open sores.
Another is a foul-smelling odor from the affected part of the body.
How is it treated?
Doctors have to remove the larvae, sometimes through surgery.
Do not try to remove or dispose of the maggots yourself, the CDC
says.
Are more human or animal cases expected in the U.S.?
It's possible.
Scientists for decades were able to control the bug by releasing
billions of sterilized male flies, but lapses in the that work and
the migration of people and animals helped them spread northward
into Central America and Mexico more recently.
There are new genetic techniques being developed to stop them, and
the U.S. government is ramping up its work to control the parasites.
But they remain a concern.
“I don't know if it's going to come back to the United States,”
Scott said.
If it does, the Texas-Mexico border area is likely to be the first
place to see it, he said.
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