Screwworm Outbreak Hits Mexico, Infects Humans and Animals

The screwworm infestation, caused by the parasitic larvae of Cochliomyia hominivorax, continues to spread across southern Mexico despite containment efforts by federal and local authorities. The disease has now affected seven species, including humans, following the first confirmed case in a 77-year-old woman from Acacoyagua, Chiapas.

Over 780 Cases Reported Across Multiple States

According to data from the World Organisation for Animal Health (OIE), reported by the Mexican government, more than 780 cases of myiasis—infestation by screwworm larvae—have been documented in animals and humans across Campeche, Tabasco, Quintana Roo, Yucatán, and Chiapas.

The outbreak began in November 2024 with the first case detected in cattle. Since then, the infestation has expanded to horses, dogs, goats, sheep, pigs, and now humans. The latest OIE report, dated April 15, 2025, details the following case distribution:

• Chiapas: 443 cases, predominantly in cattle (403), with additional infections in sheep, dogs, horses, and pigs (7 total).
• Tabasco: 204 cases, affecting cattle, dogs, horses, goats, and pigs (7 total).
• Campeche: 99 cases, found in cattle, dogs, horses, goats, and pigs (3 total).
• Quintana Roo: 12 cases in cattle.
• Yucatán: 25 cases in cattle.

First Human Case Confirmed

Last Friday, Mexico’s Ministry of Health confirmed the first human case of myiasis caused by Cochliomyia hominivorax in the elderly woman from Chiapas, who remains in stable condition. The ministry emphasized that while the disease primarily affects livestock, human cases are rare but possible.

In response, federal agencies, including the Ministry of Agriculture and the National Service for Agrifood Health, Safety, and Quality (Senasica), have intensified epidemiological surveillance and control measures. However, the infestation persists due to the mobility of the parasitic fly, which lays eggs on living tissue, leading to larval feeding and severe tissue damage in infected mammals.

Authorities Struggle to Contain Outbreak

Despite ongoing efforts, the spread of screwworm myiasis has accelerated, driven by the fly’s airborne dispersal and reproductive cycle. The Mexican government has assured the public that no additional human cases have been identified but continues to monitor the situation closely.

The Ministry of Health reiterated that screwworm infestation is primarily an animal health issue but acknowledged the need for heightened awareness and preventive measures in affected regions.