The New World screwworm is resurging across North America, impacting both humans and livestock. Recent data from Mexican researchers indicates the parasite is moving north from Mexico into the United States.
The collapse of the 2003 Mexico-free status
For decades, international eradication efforts successfully pushed the New World screwworm (NWS) south of the Panama border. This biological barrier effectively protected North American agriculture and public health for a generation . Mexico was even officially declared free of the parasite in 2003, but that progress has been undone.
According to the report, livestock infections began reappearing in Mexico in late 2024, signaling a significant northward migration of the species. this resurgence suggests that the previous containment boundaries are no longer sufficient to prevent the parasite from re-establishing itself in higher latitudes.
204 human cases and the rising death toll in Mexico
Mexican researchers have documented a concerning rise in human myiasis, or maggot infestation, as the parasite moves through the region. Between April 2025 and March 2026, the study identified 204 reported human cases of the scewworm. While most of these cases involved men with infestations on their lower limbs, the biological impact has been fatal for several individuals.
The report states that six people died following their infestation, with one death being attributed directly to the New World screwworm. This data highlights the direct correlation between animal and human helth, as reported human cases in Mexico tended to be higher in regions where animal cases had similarly surged.
How NWS maggots burrow into living flesh
The New World screwworm larvae are biologically distinct from many other fly species due to their preference for feeding on the living flesh of warm-blooded animals. The flies lay eggs on a host via open wounds or mucous membranes, where the maggots then use their sharp mouth hooks and screw-like bodies to burrow deep into the tissue. This invasive behavior causes extensive tissue damage and significantly raises the risk of life-threatening secondary infections.
To combat this, researchers emphasize that coordination between human health, animal health, wildlife, and agricultural sectors will be essential to guide prevention and control measures.. As the report indicates, the threat is not merely an agricultural issue but a significant public health concern for any warm-blooded host in the path of the fly's expansion.
Will sterile male fly releases halt the U.S. expansion?
U.S. officials have implemented containment measures around all identified cases to prevent a wider outbreak. A primary component of this strategy is the release of sterile male flies, a method that served as the lynchpin for previous eradication programs. howeever, several critical questions remmain regarding the long-term success of these interventions.
It is currently unclear whether these localized containment efforts can prevent the parasite from making a full-fledged comeback in the United States. Furthermore, because the northward spread of the NWS fly is expected to continue, experts suggest that surveillance and fly-suppression activities must be implemented proactively at the leading edge of expansion. While the Centers for Disease Control and Prevention (CDC) currently considers the overall risk to the public to be very low, the rapid increase in human cases in early 2026 suggests that the threat could escalate if the parasite gains a permanent foothold.
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