An expert shares everything consumers need to know
September 2, 2025
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The U.S. has identified a case of New World Screwworm (NWS) in a Maryland resident who had recently traveled to El Salvador.
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NWS isnt endemic to the U.S., but its important for travelers to be aware of the risks.
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U.S. cattle could be at a high risk of NWS.
The U.S. Department of Health and Human Services (HHS) and the U.S. Centers for Disease Control and Prevention (CDC) identified a case of New World Screwworm (NWS) in the U.S.
The case was linked to a Maryland resident who had recently traveled to El Salvador.
As the U.S. Department of Agriculture is conducting an ongoing investigation, what do consumers need to know about NWS?
Dr. Heather Walden, an associate professor in the University of Florida College of Veterinary Medicine, shared her knowledge with ConsumerAffairs, highlighting everything consumers need to know about this parasite.
What do you need to know?
Dr. Walden explained the top things that consumers need to know about NWS.
First, NWS is not endemic to the United States and is of primary concern in areas of central and South America, she explained. The US works diligently with other countries to prevent geographic spread into the US and other areas and the last U.S. outbreak was limited to the Florida Keys nearly a decade ago. This was quickly controlled using sterile release of male flies to effectively break the life cycle.
How is it transmitted?
If youve never heard of screwworm before, Dr. Walden shared the process of how its transmitted.
The NWS is transmitted through adult female flies laying eggs in fresh, non-contaminated wounds, she said. Any fresh wound will suffice, even a tick bite.
Once eggs are laid, they hatch quickly and the larvae (maggots) feed on living tissue as they develop. This takes time, it is not instantaneous. Development typically occurs over a week.
What is the impact on the U.S.?
Dr. Walden explained that while a full-fledged outbreak isnt likely, there are ways that NWS can affect the U.S.
The NWS can have devastating economic impacts on cattle production, which is why the U.S. works hard to keep this fly out of our cattle herds, Dr. Wladen said. The flies feed on living tissue, and if left untreated, animals infested with NWS can die.
Infestations are also painful as the larvae are feeding on living tissue. These flies can also infest most vertebrate hosts, including humans, wildlife, and our companion animals.
Safe travel
Because the NWS is more likely to be found in other countries, Dr. Walden urges travelers to be mindful on their trips.
Be aware of parasites and other pathogens endemic to countries where travel is planned, she said. Those most at risk for NWS include those along the southernmost border or those that travel to endemic areas.
If fly larvae are noticed on any open wounds, seek medical care by contacting your physician or veterinarian and get them removed and identified. With proper care and quick intervention, the outcome is usually favorable.