Introduction/Background
The New World Screwworm (NWS), Cochliomyia hominivorax (C. hominivorax), is an obligate parasitic fly that causes myiasis in warm-blooded animals, leading to severe tissue damage, secondary infections, and significant economic losses. Myiasis caused by C. hominivorax is a significant cause of mortality among newborn calves, in addition to directly impacting milk production, fertility, feed conversion rates, and animal weight gain. In other animal species (including humans), the damage caused by infestation is associated with severe health complications and mortality in untreated cases. Following its eradication from Mexico in 1991 and subsequent regional elimination across Central America by 2006, reemergence in Central America beginning in 2023 and subsequent detection in Mexico (late 2024) have raised concern regarding rapid geographic expansion and potential re-establishment. Favorable climatic conditions, host availability, and livestock movement contribute to its spread, representing a major threat to animal health systems.
Methods
Official epidemiological reports, dashboards, and technical bulletins from the Servicio Nacional de Sanidad, Inocuidad y Calidad Agroalimentaria of Mexico (National Service for Agri-Food Health, Safety, and Quality; SENASICA), and the World Animal Health Information System of the World Organization for Animal Health (WOAH-WAHIS) were reviewed. Data regarding cumulative case counts, geographic distribution, affected species, lesion types, and control strategies were compiled to characterize the current epidemiological situation and identify key challenges for containment and eradication efforts. A confirmed NWS case was defined as an animal with myiasis-compatible lesions and confirmation of C. hominivorax larvae through official diagnostic or surveillance reporting systems. For swine-specific analyses, WOAH-WAHIS reports were interpreted at the report-line level, where each report included the number of swine cases and the associated susceptible pig population. Figures and epidemiological visualizations were generated with R using ggplot2 and spatial analysis packages.
Results
As of May 5, 2026, a total of 23,076 cumulative NWS cases had been reported in Mexico since the first detection in November 2024. Reported cases remained concentrated in southern and southeastern states, including Chiapas, Oaxaca, Veracruz, Yucatán, Tabasco, and Campeche, with evidence of progressive geographic spread (Figure 1).
Cattle accounted for most reported cases (65.4%), followed by canines (17.6%), while swine represented a smaller but epidemiologically relevant proportion (6.8%; 1,575 confirmed cases).
Other species collectively accounted for approximately 10.1% of cases (Figure 2).
Despite their lower frequency, swine cases remain relevant due to their association with specific production systems and management-related risk factors. The reduced incidence in pigs is likely linked to intensive production systems, higher biosecurity standards, and continuous monitoring, which may limit exposure. Reported swine cases were predominantly associated with backyard or low-biosecurity production systems.
Across species, infestations were consistently associated with pre-existing lesions. The most frequently reported lesion types included umbilical infections (4,297 cases) and traumatic wounds (4,124 cases), followed by injuries related to barbed wire, fighting, and other causes (Figure 3). These lesions facilitate larval infestation and rapid disease progression characterized by tissue destruction and secondary infection.
Swine-related WOAH-WAHIS reports accumulated between November 24, 2024, and May 5, 2026, were primarily concentrated in southeastern Mexico, particularly in Chiapas, Oaxaca, Veracruz, Yucatán, Tabasco, and Campeche (Figure 4). Most reported swine cases were associated with backyard or low-biosecurity pig production systems, while only one report corresponded to an intensive commercial swine operation in Chiapas. However, because pigs can suffer frequent injuries from traumatic objects, castrations, tail docking, birth injuries, as well as umbilical wounds in newborn piglets, they remain susceptible to NWS myiasis.
As of April 2026, 253 cases of myiasis caused by NWS had been reported in the human population of Mexico. The states with the highest frequency of cases were Chiapas, Oaxaca, and Yucatán. Older patients with diabetes or other immunosuppressive conditions are at higher risk of developing myiasis due to poor circulation, reduced pain perception, and impaired wound healing.
Control efforts have relied on a national regionalization strategy dividing the country into affected, buffer, and free zones, allowing targeted implementation of surveillance, movement control, and intervention measures. Control strategies include activation of the National Animal Health Emergency System (DINESA), enhanced surveillance, active case notification, diagnostic confirmation, movement control and inspection, treatment of affected animals, producer education campaigns, trapping systems, and deployment of sterile insect technique (SIT) as the cornerstone of eradication efforts. In parallel, industry organizations such as the “Organización de Porcicultores Mexicanos (OPORMEX)” have contributed to reinforcing biosecurity practices and communication within the swine sector.
Currently, only one sterile fly production facility exists worldwide, belonging to the Panama-United States Commission for the Eradication and Prevention of Screwworms (COPEG), with a capacity to produce 100 million sterile flies per week. Mexico is expected to establish a sterile fly production facility with a capacity of 100 million flies per week by 2026, and by 2027, the United States will have a production capacity of 300 million flies per week. With this technology and international collaboration, it is hoped that this pest will once again be eradicated in Mexico and Central America.
Conclusions
The reemergence of NWS in Mexico represents a significant sanitary and economic threat. While swine is less frequently affected due to intensive production systems, their involvement highlights the importance of targeted vigilance in backyard and low-biosecurity production systems. Eradication efforts face multiple challenges, including wide geographic dispersion in environmentally suitable regions, continuous animal movement, operational complexity of large-scale sterile insect programs, and the need for sustained coordination among stakeholders.
The implementation of zonal control strategies supports containment efforts but also underscores the difficulty of maintaining disease-free areas under conditions of ongoing case detection. The high volume of field reports and surveillance activities further highlights the operational burden on animal health systems. Strengthening early detection, maintaining high biosecurity standards, and ensuring rapid response capacity—supported by coordinated efforts between authorities and industry groups such as OPORMEX—will be critical to limit spread and support long-term eradication. Selected field cases from Mexico and Central America will also be presented during the oral presentation to highlight operational challenges and mitigation strategies associated with NWS under field conditions.
References
SENASICA. Epidemiological reports, dashboards, and technical bulletins on New World screwworm (2024–2026). Available from: https://www.gob.mx/senasica Accessed May 2026.
Valdez-Espinoza UM, Fadda LA, Marques R, Osorio-Olvera L, Jiménez-García D, Lira-Noriega A. The reemergence of the New World screwworm and its potential distribution in North America. Scientific Reports. 2025; 15:23819. https://doi.org/10.1038/s41598-025-04804-9
World Organization for Animal Health (WOAH). World Animal Health Information System (WAHIS). Available from: https://wahis.woah.org/. Accessed May 2026.
