The United States has confirmed its first human case of travel-associated New World screwworm - a flesh-eating parasite that can kill its host if left untreated.
Andrew G. Nixon, spokesman of the Department of Health and Human Services (HSS), confirmed to Reuters that the case was discovered in a Maryland resident who had recently travelled to El Salvador.
He said the Centres for Disease Control and Prevention (CDC) confirmed on August 4 that the parasite present was the larvae of the New World screwworm fly.
According to Nixon, the risk to public health in the United States from this shocking introduction is currently ‘very low’. He also emphasised that no animal cases have been confirmed this year.
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While human infections can be fatal, they are rare, with most cases being able to be treated.
Previously, the US Department of Agriculture (USDA) has stated that screwworms have been making their way north into Mexico from other parts of Central America.
The fly is endemic in Cuba, Haiti, the Dominican Republic and some South American nations, as per NBC News.
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Tyla has contacted the US Department of Health and Human Services for further comment.
What are screwworms?
Cochliomyia hominivorax, known more commonly as the New World screwworm fly, is a species of parasitic blowfly whose larvae eat the living tissue of warm-blooded animals, particularly cows.
Described as a ‘devastating pest’ by the USDA, the screwworm - referring to the maggots' feeding behaviour as they burrow - was originally eliminated from the United States in the 1960s.
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While the flies are comparable the size to common houseflies, the screwworm larvae are usually between 6.5 to 17mm long, as per the CDC.
You will know you’re looking at one of the pests if the larvae are taped anteriorly, truncated posteriorly, and have encircling bands of short, pointed spines on each body segment.
Common signs of screwworm infection
The female New World screwworm fly will lay eggs on the edges of open animal wounds - whether it be on the nose, the mouth, or even on the umbilical cord of a newborn.
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Eggs are creamy white, according to the Equine Disease Communication Centre (EDCC) and can be laid in wounds as small as tick bites.
Within 12 to 24 hours, the eggs will hatch, and the larvae will emerge to feed on your warm-blooded pet for around seven days.
They can create cavernous, foul-smelling lesions up to 10–12cm in diameter.
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Some symptoms that can indicate your animals are suffering from burrowing screwworms include:
- Irritated behaviour
- Head shaking
- The smell of decay
- Visible presence of fly larvae (maggots) in wounds
What to do in case of screwworm infection?
If you see maggots on a wound, you should immediately contact your healthcare provider or local veterinary service.
Currently, there are no animal drugs approved by FDA for the treatment or prevention of the larvae in animals, as per the USDA.
However, the FDA provides information to support vets with identifying FDA-approved animal drugs labelled for indications other than NWS myiasis that scientific literature indicates may be effective to prevent or treat NWS myiasis, the agency stated.
What have CDC said about the infestation?
Speaking to Tyla, the CDC said: "In coordination with the Maryland Department of Health, investigated a confirmed case of travel-associated New World screwworm in a patient who returned from travel to El Salvador.
"The case was confirmed by CDC through telediagnosis (i.e., expert review of submitted larvae images) on August 4, 2025.
"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." For more information on how screwworms affect people or to report human disease, you should get in contact with the CDC.
Ella Scott