Screwworm Mutation Threatens Eradication, Experts Warn

Mérida, Yucatán — Recent studies by the Panama-United States Commission for the Eradication and Prevention of the Screwworm (Copeg) reveal significant biological changes in the screwworm fly, making its spread faster and eradication more challenging, according to veterinarian and researcher Iván Rodríguez Vivas of the Autonomous University of Yucatán (UADY).

Accelerated Reproduction Poses Greater Threat

Rodríguez Vivas reported that female screwworm flies have increased their egg-laying capacity from approximately 2,000 to 5,000 eggs in their reproductive lifespan. Additionally, male flies now mature in as little as two to four days and mate with more females—between six and 16 per male—further accelerating infestations.

“The cases are increasing, and the infestations are becoming more aggressive, affecting both animals and humans,” Rodríguez Vivas stated.

Urgent Need for Sterile Fly Production Plant

The researcher urged authorities to expedite the construction of a facility to produce sterile screwworm flies, a critical measure to control the outbreak. The United States has pledged an initial $21 million to establish the plant, which must produce at least 100 million sterile flies weekly to be effective.

Rodríguez Vivas emphasized that results would take at least a year, making immediate action essential. “The problem is growing more severe. We already have six human cases in Chiapas and over 1,500 animal cases nationwide,” he said.

Confirmed Cases in Yucatán

The Yucatán Ministry of Rural Development has confirmed five screwworm cases in the state: three in Tzucacab (affecting sheep and cattle), one in Halachó’s Cepeda district (a calf), and one in Mérida (a dog). No human cases have been reported in Yucatán, though the presence of the parasite was first detected on March 7.

Authorities Assert Outbreak is Under Control

The Ministry insists the outbreak is contained due to coordinated prevention efforts with Mexico’s National Service for Agrifood Health, Safety, and Quality (Senasica). Nine interstate agricultural inspection checkpoints have been established in seven municipalities: Maxcanú, Halachó, Santa Elena, Peto, Chemax, Tizimín, and Tixcacalcupul.

Local livestock associations agree that Yucatán has successfully limited the spread among cattle herds.

About the Screwworm

The screwworm is the larva of the Cochliomyia hominivorax fly, which lays eggs in open wounds, mucous membranes, or body cavities. Upon hatching, the larvae consume living tissue, causing a severe infection known as myiasis.