According to an assessment from Mexico’s Ministry of Health in July, there have been more than 500 human cases of New World Screwworm reported since the flesh-eating parasite reinvaded that country in 2024.
A study published in the journal Emerging Infectious Diseases last week analyzed the information on more than 200 confirmed cases reported between April 2025 and March 2026 found the infestation rate is increasing.
Among the 200 confirmed cases in that study, six deaths were reported, and at least one death was directly attributable to the infestation.
Although human screwworm infections represent a small fraction of the overall cases, an infestation can be severe and quickly debilitating.
Infestations occur in people with breaks in the skin, including very small wounds.
They can also occur in the eyes, ears, nose, mouth, and any other exposed mucosal tissues.
After these flies lay eggs in the wounds, inflamed tissue, mucous membranes, and orifices of warm-blooded creatures, maggots hatch within a day and begin ravenously feasting on the flesh of their hosts.
- Keep any open skin wounds clean and securely bandaged
- Wear protective clothing like long sleeves, pants, and socks
- Spray outer clothing with 0.5% permethrin
- Use window screens and other measures to keep flies away.
According to agricultural officials, the New World screwworm fly was endemic in Mexico and the United States until a decades-long eradication programs was adopted by both nations.
The fly’s populations were wiped out through massive aerial releases of sterilized male flies, a technique that works because female NWS flies only mate once in their lifespans.
Researchers say the screwworm flies were considered to be fully eradicated in Mexico by 2003, and Panama declared eradication in 2006, keeping an active biological barrier along the border with South America.
In 2022, that barrier was breached, and cases were being reported in Mexico by 2024.
Since those first cases, more than 36,000 animal cases of screwworm infection have been reported in Mexico, with nearly 2,000 active as of Aug. 5, according to the USDA.
