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, officials also reported cases in dogs, horses, sheep, and humans.
Local media reports indicate that dozens of people have been treated for the infestation in hospitals across the southern Mexican states of Campeche and Chiapas.
This surge in affected animals follows the confirmation by US health authorities of the first human case in a patient returning from El Salvador.
NWS was declared eradicated in the US in 1966 and Mexico followed suit in 1991, yet it remains prevalent in tropical and subtropical regions of Central and South America and has recently started spreading northwards, with the first new case reported in Mexico in November 2024.
The female New World screwworm fly (Cochliomyia hominivorax) lays its eggs in or near open wounds on warm-blooded animals. The larvae hatch and burrow into the wound, feeding on living flesh. This condition is known as myiasis, which, if untreated, can cause severe damage or even prove fatal.
Health officials caution that while fatal cases in humans are rare, people with pre-existing health conditions and the elderly should exercise extra care. An 86-year-old woman in Campeche state died from complications due to skin cancer aggravated by a screwworm infestation.
Those at the highest risk are individuals working with livestock or living in rural areas where infested animals are present. The CDC has advised individuals who have traveled to regions where screwworms are prevalent to be vigilant of symptoms such as unexplained skin lesions and seeing maggots in open wounds.
The Mexican health ministry encourages preventive measures such as keeping open wounds clean and covered and using insect repellent, as well as seeking medical assistance for suspected infestations.
