Mexico Confirms First Human Case of Screwworm Myiasis

Mexico's Ministry of Health confirmed the country's first-ever human case of myiasis caused by the New World screwworm, a flesh-eating parasitic infection that has long plagued livestock across the Americas.

The infected patient is a 77-year-old woman from the town of Acacoyagua in the southern state of Chiapas. According to health authorities, she is currently in stable condition and receiving antibiotic treatment.

Myiasis is a parasitic skin disease triggered when fly larvae invade open wounds and feed on living tissue.

The New World screwworm fly, in particular, lays its eggs in open sores, and the hatching larvae burrow deep into flesh, consuming their host from the inside out.

The condition is extremely painful and can be fatal in humans and animals. No specific cure is currently available.

For decades, countries across the Americas have invested billions in eradicating this deadly parasite. Originally native to South America and the Caribbean, the screwworm fly was nearly eliminated from North America through sterilization programs and a fly-free barrier zone established along the US-Mexico border.

By 1986, Mexico had successfully controlled the parasite, following a similar effort in the United States during the mid-20th century, which helped farmers avoid annual losses exceeding $100 million. However, a resurgence in cases has been reported since 2023, raising concern among health and agriculture officials.

According to the U.S. Department of Agriculture (USDA), the screwworm has reemerged in several countries. Since last year, cases have been confirmed in Panama, Costa Rica, Nicaragua, Honduras, Guatemala, and now Mexico. The USDA warns that the parasite could begin spreading further north if not properly contained.

The New World screwworm fly can lay up to 300 eggs at once and produce thousands more throughout its short lifespan of 10 to 30 days. Even small wounds, such as those caused by a tick bite, can attract the fly. Once the eggs hatch, larvae with sharp, hooked mouths burrow into flesh, enlarging wounds and feeding on tissue, which increases the risk of secondary infections.

A World Health Organization study found that human myiasis has a fatality rate of approximately 3 percent.

The USDA has urged pet owners and livestock handlers to monitor animals for swollen or infected wounds, check for visible larvae or eggs, and seek immediate veterinary care if symptoms appear.