Collaborative Efforts to Combat the Cattle Screwworm in Latin America

Mexico and Guatemala have joined forces to tackle the resurgence of the cattle screwworm, a pest that poses significant risks to livestock and human health. This collaborative effort aims to implement effective control measures and prevent the spread of the screwworm across Central America.

The governments of Mexico and Guatemala have agreed to strengthen their cooperation to prevent the entry of the cattle screwworm, a highly dangerous pest, into their territories. This decision, announced by Mexico’s Ministry of Agriculture and Rural Development (Sader), underscores the commitment of both nations to safeguard human and animal health from this dangerous threat.

The cattle screwworm, known scientifically as Cochliomyia hominivorax, causes myiasis, a parasitic infestation affecting animals and humans. The larvae of this fly feed on the living tissue of their hosts, resulting in severe skin lesions. This pest poses significant risks to livestock, leading to high mortality rates and reduced milk and meat production productivity. While the screwworm has been eradicated in the United States, Mexico, and Central America, it remains a problem in parts of South America and the Caribbean.

Following a meeting between Mexico’s Agriculture Secretary Víctor Villalobos Arámbula and Guatemala’s Minister of Agriculture, Livestock, and Food, Maynor Estrada, both countries committed to a comprehensive model of international cooperation. This collaboration, which is crucial in the fight against the screwworm, aims to curb the spread of the pest by sharing technical knowledge and control strategies through Mexico’s National Service for Health, Safety, and Food Quality (Senasica). The goal is to implement effective containment measures across Central America.

Mexico is also establishing inspection facilities along its southern border to apply sanitary treatments to cattle entering from Guatemala, preventing the introduction of screwworms and other pests. Villalobos Arámbula emphasized the need for regional measures, noting the dispersal of screwworms in countries like Panama, Nicaragua, and Costa Rica, which poses a latent risk to the livestock sector in the region.

To bolster containment efforts, Mexico plans to collaborate with Panama to enhance the operational capacity of the sterile fly production plant. This biological control strategy involves releasing sterile male flies to reduce the population of screwworms. Additionally, Mexico offers Guatemala a tele-diagnosis service, enabling experts to confirm the presence of screwworms through remote analysis of samples sent via microscope images.

Historically, the cattle screwworm caused significant economic losses in the southern United States and Mexico, amounting to over $100 million annually. Decades of coordinated efforts and substantial financial investment eradicated the pest from North and Central America by the late 20th century. However, since 2023, there has been a resurgence of cases in Panama, Costa Rica, and Nicaragua, prompting urgent and immediate action.

The re-emergence of the screwworm in Central America has raised the alarm. Costa Rica, for example, declared a national emergency after detecting the pest in all seven of its provinces within ten months. The resurgence of screwworms in such a highly susceptible population has led to rapid spread and significant economic impact. As of June 2024, Costa Rica reported 2,456 cases, predominantly affecting cattle, with some occurrences in dogs, goats, sheep, horses, and even humans. This urgent situation calls for immediate and sustained action.

Nicaragua has also confirmed 55 cases, while Honduras, El Salvador, Belize, and Guatemala have yet to report any infestations. In response to the threat, Mexico’s Senasica has increased inspections at airports, ports, and borders and distributed informational materials to all states to raise awareness and prevent the pest’s spread.

The Economic and Social Costs of Screwworm Infestations

Screwworm infestations severely impact livestock, leading to reduced meat, leather, and milk production. If left untreated, the larvae’s wounds can be fatal. The social costs are also high, necessitating constant inspection and treatment of infected animals. In humans, the larvae can cause serious health issues, including skin ulcers, respiratory tract obstructions, ear canal infections, abdominal pain, fever, and, in rare cases, brain migration. These health issues not only affect the individual but also result in increased healthcare costs and potential loss of productivity, underlining the significant economic impact of this pest.

Central American countries are striving to prevent the screwworm from advancing northward. Past eradication efforts in the United States and Mexico cost approximately $955 million, while Central America’s efforts totaled $341 million. A potential reinfestation in the United States could cost over $1 billion annually, underlining the significant economic impact of this pest.

Biological Control and Future Directions

The biological control programs for eliminating this parasitic infestation have been crucial. These programs involve producing, sterilizing, and releasing sterile male flies to decrease the pest population. The sterile fly technique, developed in the mid-20th century, remains a cornerstone of the eradication strategy.

1991, Mexico declared itself free of the screwworm, followed by Belize and Guatemala in 1994, El Salvador in 1996, Nicaragua in 1998, and Costa Rica in 2000. However, the disease remained endemic in South America and the Caribbean, with the Darién Gap between Panama and Colombia serving as a containment barrier.

The situation changed in July 2023 when Panama reported cases beyond the Darién Province, extending 200 kilometers from the Costa Rican border. Despite intensified preventive and surveillance measures, the disease reached Costa Rica. Alexis Sandí Muñoz, head of epidemiology at Costa Rica’s National Animal Health Service (SENASA), explained that the infestation spread rapidly within the country, affecting the Pacific coast, known for its biological reserves and livestock operations, and the Atlantic coast.

In February 2024, Costa Rica declared a national emergency due to the resurgence of the screwworm. The country reports new cases daily, underscoring the need for sustained efforts to mitigate and control the disease. As of June 25, 2024, Costa Rica had registered 2,456 cases, with 77% in cattle and 14% in dogs. Cases have also been reported in goats, sheep, horses, and seven humans. This situation highlights the need for continuous and coordinated efforts to combat the screwworm.

A Coordinated Response is Crucial

The resurgence of the cattle screwworm in Central America poses a significant threat to livestock and human health. The cooperative efforts between Mexico and Guatemala and regional collaborations are essential to contain and eventually eradicate this pest. By sharing technical knowledge, implementing biological control strategies, and enhancing surveillance and preventive measures, these countries aim to protect their agricultural sectors and prevent further spread.

As the situation evolves, Central American nations must remain vigilant and proactive in combatting the screwworm. The stakes are high, with significant economic and social costs associated with the infestation. There is hope for controlling and eradicating this persistent threat through coordinated action and international cooperation.

New Outbreaks, New Challenges

Over the past year, Panama, Costa Rica, and Nicaragua have been applying the lessons learned decades ago, but the new outbreaks have unique characteristics. Sandí Muñoz points out that the recent outbreaks cannot be attributed to a single cause. Several factors contribute to the resurgence of Cochliomyia hominivorax:

Environmental Crises and Climate ChangeAlthough no specific studies attribute the spread of Cochliomyia hominivorax to climate change, Costa Rican scientist Sandí Muñoz indicates that its effects will impact animal behavior, including insects. One possible scenario observed in other species is that distribution patterns change with global temperature increases. Entomologists agree that the fly’s average flight range is about 20 kilometers. However, they may travel more distances due to climatic conditions and wind direction. A study published in 2019 projected that if the fly reestablishes in North America, “climate warming by 2045-2055 will expand the area of favorability and increase the frequency and severity of outbreaks.”

A Susceptible PopulationThe flies responsible for the recent outbreaks seem to use wild animals as their primary reservoirs. Sandí explains that “the wildlife environment favors their maintenance and dispersal.” Wounds are more common in wildlife, increasing the chances of the larvae causing myiasis.

Migratory FlowsThe Darién Gap has seen increased movement of people, pets, and goods in recent years. This transboundary situation has historically been linked to the greater spread of diseases. The evasion of controls for animal movement is a risk factor in some areas.

More Resistant and Aggressive Strains “We have spoken with colleagues from South American countries where Cochliomyia infestations are endemic. They have observed that outbreaks in the last three years have been more severe, which we have also seen in Costa Rica,” Sandí notes. “The larvicidal products available are not as effective as before.” Severe consequences have also been observed: animals losing eyes and udders and severely impacting humans. “This is a robust fly strain, resistant to treatments, showing a greater dispersal capacity than in the 1990s.”

Preventing the Spread Northward

Efforts to prevent the disease from reaching Mexico and the United States aim to avoid past scenarios. According to an Entomology Today post, “keeping flies away saves the United States $1.3 billion in cattle damage annually.” In Mexico, after ranchers in Durango expressed grave concern, the federal government announced it would strengthen prevention against the screwworm. The plan includes the early activation of the National Animal Health Emergency Device (Dinesa), “which mobilizes all capacities of Senasica [National Service for Health, Safety, and Food Quality] to prevent and avoid the spread of the pest,” according to an official statement. Additionally, two sanitary barriers will be established in southern Mexico, and canine units will be trained to detect screwworms.

Besides the economic impact, allowing the disease to spread could threaten human and pet health. Citizens must attend to animal wounds and, in the case of people, be cautious with vulnerable groups such as older people, people with disabilities, children, and people experiencing homelessness.

The current control plan in affected regions is based on four pillars. Sandí Muñoz explains that the first is passive epidemiological surveillance. In Costa Rica, they have a WhatsApp line and an email for reporting and analyzing cases. The second is informing the public. Since the region had no myiasis caused by Cochliomyia for several years, some producers are unaware of it today. Authorities disseminate information about the fly and the disease, how to prevent it, identify lesions, and treat cases. It is crucial to kill the screwworms on the wound and then extract them to prevent them from reaching the ground and completing their cycle. To prevent sites conducive to screwworm infestations, veterinarians suggest taking extra precautions with calf navels, surgical wounds, dehorning, and livestock identification. They also recommend addressing the stray dog population. The third pillar is reinforcing control in livestock movement.

Sterilizing Flies

However, the flagship strategy of control programs—crucial for eradication in the United States and Mexico—is undoubtedly breaking the reproductive cycle with the sterile fly technique (SIT). This method involves breeding male flies sterilized by radiation and releasing them to mate with wild females, resulting in infertile eggs. Over time, the wild fly population decreases.

Mexico declared itself free of this pest after releasing approximately 250 billion sterile flies over 19 years in 58,000 flight hours. In that campaign, the United States provided 80% of the funds and Mexico 20%. Panama has a sterile fly production plant. Since its opening, it has produced insects for release on its border with Colombia. Although the plant did not operate at total capacity for some time, it has increased its production from 20 million to 90 million sterile pupae weekly over the past year, dispersing them in Panama, Costa Rica, and Nicaragua since July 31, 2023. Given the current aggressive variant, Sandí Muñoz details that they are developing a new sterile strain to compete with wild males.

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Despite the weekly aerial release of nearly 15 million insects, Costa Rica still needs to manage to stop the disease’s progression. The SENASA official explains that they maintain communication with health authorities from the affected countries as part of the emergency. A partnership with the United States Department of Agriculture (USDA) was signed to invest resources in more excellent sanitary education, hiring personnel, and obtaining vehicles for field surveillance.

The fight against the screwworm in Latin America continues, with regional collaboration, biological control strategies, and ongoing vigilance playing crucial roles in combating this persistent threat.