The regional health crisis caused by the cattle screwworm (Cochliomyia hominivorax) escalated to a new stage this week, after the first human case in the United States was confirmed in a patient from Maryland who had traveled to Central America.

The discovery has rekindled international concerns about a plague that has resurfaced in Panama since 2023 and spread to all Central American countries and Mexico, with serious consequences for animal and public health, and the livestock economy.

In Panama, the epidemiological bulletin of the Panama-United States Commission for the Eradication and Prevention of the Cattle Screwworm (Copeg) reports, as of week 28 of 2025—July 6-12—a cumulative total of 49,578 cases, with 672 new diagnoses in the last recorded week. Of the total, 85% correspond to cattle, but 161 cases have also been confirmed in humans and multiple reports in domestic and wild species, including deer, mules, kinkajou, rabbits, sloths, porcupines, and leopards, reflecting the breadth of the impact.

The situation is critical in several countries. Currently, the screwworm remains in the eradication phase in Panama, with cases detected in all provinces except the Guna Yala region. Regionally, cases have also been reported in Costa Rica, Nicaragua, Honduras, Guatemala, El Salvador, Belize, and Mexico, where health authorities have reactivated surveillance and control programs. Meanwhile, an update on the Copeg website redirects users to consult statistics for each country.

Mexico recently reported an outbreak in Veracruz, less than 600 kilometers from the U.S. border, raising alarms at the USDA and leading to restrictions on livestock movement.

Over the past 25 years, the U.S. Department of Agriculture has invested more than $325 million in COPEG’s operational activities, infrastructure improvements, and regional support in Panama. “This investment contributes to health and food security throughout the region,” COPEG told La Estrella de Panamá through the U.S. Embassy in the country.

The adult fly Cochliomyia hominivorax lays between 200 and 300 eggs on the skin of livestock, wildlife, and humans. Upon hatching, the larvae feed on living tissue and cause maggot infestation or cutaneous myiasis.

Panama, working with the United States, successfully eradicated the screwworm from Central America after nearly two decades. Efforts began in 1998, and in 2006, the country inaugurated its only sterile fly production plant. For nearly 20 years (2006–2023), Copeg successfully maintained the biological barrier in Darién. The sterile insect technique (SIT) has been one of the pillars of parasite control and eradication.

The current situation presents several factors that favor the resurgence of the screwworm in Panama and the region. First, the Darién cattle herd has grown exponentially: it went from approximately 22,000 head in 1984, when the eradication program began, to more than 250,000 today, which increases the population vulnerable to the parasite.

Added to this are the environmental conditions. The fly thrives in warm, humid climates, and the warmer these conditions are, the faster it completes its life cycle, accelerating the hatching of its eggs. Today, the insect finds a perfect breeding ground.

Another critical factor is animal movement. The movement of infected cattle and the evasion of checkpoints facilitates the spread of the parasite to previously declared free areas.

Poor animal husbandry practices also persist, both on farms and in homes. These include wounds that are left untreated until they heal, untreated dehorning and castration, branding and earmarking without aftercare, neglected hoof trimming, and a lack of adequate umbilical cord care in newborns. These practices open the door to infestations and complicate the fight to keep the country free of screwworms.

During the Expanded Cabinet Council held in Metetí, Darién province, on August 21, COPEG director Carlos Moreno spoke with this media outlet and warned that the region is currently experiencing a “health emergency.” He emphasized that the pest not only threatens livestock farming but also public health. “We are at a turning point: we must strengthen communication with producers, educate the population, and expand scientific capacity to generate more sterile flies,” he explained.

The Ministry of Agricultural Development (MIDA), through its Director of Animal Health, Reinaldo Vivero, emphasized that prevention is key: “Minimizing wounds in livestock, treating them appropriately, and preventing the spread of live larvae can make a difference in reducing cases.”

For its part, the Inter-American Institute for Cooperation on Agriculture (IICA) provided support by delivering 150 control kits and training to producers in Darién, an area that historically served as a biological barrier to contain the spread of the disease from Colombia.

To combat the fly, Copeg increased its production capacity at the Pacora plant, going from 20 million to more than 109 million sterile pupae per week, and expanded aerial dispersal to 26 weekly flights in the region. However, demand exceeds this capacity: to contain the outbreak, it is estimated that at least 500 million sterile flies must be released weekly.

Faced with this gap, Mexico began construction of a plant in the south of the country in July, with a $51 million investment from the United States. The plant is designed to produce hundreds of millions of additional sterile flies and strengthen containment measures before the pest spreads to U.S. territory.

The last outbreak of screwworm in the United States occurred more than half a century ago. Since then, the United States has allocated millions of dollars in support of COPEG. Today, with confirmed human cases and the plague spreading throughout Mesoamerica, international cooperation is once again crucial to avoid multimillion-dollar losses and a health setback that would jeopardize the region’s food security.