The number of animals infested with New World screwworm (NWS), a flesh-eating parasite, has risen by 53% in the four weeks to mid-August, according to Mexican government data.
While infestations by the fly larvae primarily affect cattle, Mexican officials also registered cases in dogs, horses, sheep, and humans.
Dozens of people have been treated for the infestation in hospitals in the southern Mexican states of Campeche and Chiapas.
This alarming increase follows the confirmation of the first human case in the United States, linked to a patient returning from El Salvador.
NWS was declared eradicated in the U.S. back in 1966 and in Mexico in 1991, but it remains prevalent in Central and South America and has recently been spreading north, with the first new case reported in Mexico in November 2024.
Female New World screwworm flies (Cochliomyia hominivorax) lay their eggs in or near open wounds on warm-blooded animals. The eggs hatch into maggots that burrow into the wound, feeding on living flesh, a condition known as myiasis.
If untreated, myiasis can lead to significant tissue damage and even death as the larvae tear into tissues with sharp mouthparts. While fatalities in humans are rare, those with existing health conditions and the elderly should take special precautions.
Health officials announced that an 86-year-old woman in Campeche died from complications due to skin cancer exacerbated by a screwworm infestation. Most at risk are those working with livestock or residing in rural areas.
The U.S. Centers for Disease Control and Prevention advises vigilance among individuals who may have visited regions affected by screwworms. Symptoms include unexplained skin lesions and observable maggots in open wounds.
Experts stress the importance of prevention in rural areas, including maintaining clean and covered wounds and using insect repellent. Anyone suspecting infestation is urged to seek medical assistance.
