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In several Central American countries, the screwworm outbreak has triggered health alerts, with more than 40,000 cases reported in Panama, Costa Rica, Nicaragua, and Honduras as of September 2024¹. The impact goes beyond livestock health, as it also entails economic losses for producers and a potential risk to biodiversity and public health in general, with a growing number of human cases reported in the region². This pest, caused by the fly Cochliomya hominivorax, leads to severe infections by feeding on living tissue and, in some cases, causing the death of the individual. Illegal cattle ranching adds severity to the challenge, acting as a vehicle for the transmission and spread of this disease across borders and thereby increasing the risk of outbreaks in more countries in the region.

¹International Regional Organization for Animal and Plant Health (OIRSA). Regional epidemiological bulletin on the New World screwworm (NWS). Epidemiological week #39/2024 (September 22–28, 2024).

²https://www.ministeriodesalud.go.cr/index.php/prensa/61-noticias-2024/1974-salud-confirma-caso-de-miasis-por-gusano-barrenador-en-nina-condicion-migrante

The larvae (worms) of the Cochliomya hominivorax fly cause severe infections by feeding on the live tissue of animals. Photo/GETTY 

Illegal cattle movements: a key factor in disease transmission 

Illegal cattle ranching is one of the main threats facilitating the spread of the screwworm. It is estimated that this illicit industry moves around one million head of cattle per year throughout the region³. Operating outside of legal frameworks, these activities evade sanitary regulations, allowing diseases and parasites such as the screwworm to spread uncontrollably—affecting livestock, wildlife, and in some cases, humans. 

³InSight Crime (2022). Inside the Cattle Smuggling Trade from Central America to Mexico. https://insightcrime.org/es/investigaciones/vacas-lecheras-contrabando-ganado-centroamerica-mexico/

In addition, illegal ranching undermines traceability—the ability to track the origin of an outbreak. Without proper traceability, responses to disease outbreaks are slower and less effective. 

Furthermore, illegal cattle ranching is responsible for up to 90% of recent deforestation in the Great Forests of Mesoamerica. The destruction of these ecosystems not only contributes to climate change but also disrupts natural balance, enabling certain species and pathogens to thrive and increasing the risk of zoonotic outbreaks. 

In Costa Rica, the screwworm has also affected wildlife such as the tapir (Tapirus bairdii), as shown in this case of an animal that died despite veterinary attention. Photo by María Calderón. 

The economic cost of the screwworm: a regional threat 

The spread of the screwworm and other zoonotic diseases threatens communities that depend on livestock for their livelihoods, as well as the regional economy. Without coordinated responses and effective control of illegal ranching, the problem could worsen—affecting people and ecosystems alike. 

Studies estimate that in the event of a significant screwworm outbreak in the region, the total cost of eradication could reach USD 830 million. However, the economic impact on the livestock industry could be even greater. A study analyzing a hypothetical scenario in which the disease became endemic in the United States projected annual industry losses of up to USD 1 billion⁴. 

⁴SENASICA. Analysis of the Impact of the Screwworm in Mexico. https://dj.senasica.gob.mx/Contenido/files/2021/enero/An%C3%A1lsisSocioecon%C3%B3micoGBG_2f22a99d-0284-4899-bdb8-56101f4ee9f9.pdf

What is the solution? 

1. Strengthen livestock regulation: It is essential to enforce strict control over the movement of cattle in high-risk areas. Authorities must focus on identifying and eliminating illegal ranching, ensuring that all operations remain under sanitary supervision to prevent the spread of diseases. Traceability plays a crucial role—by tracking the source of an outbreak, containment measures can be implemented more quickly and effectively. 
2. Active surveillance and screwworm control: Screwworm management strategies include constant livestock monitoring and the application of targeted treatments to eliminate the pest. These efforts should be complemented with awareness campaigns aimed at local producers, encouraging compliance with animal health measures and the timely reporting of any suspected cases. 

Call to action 

National and local authorities must take decisive action to control illegal cattle ranching and strengthen epidemiological surveillance. Investing in the health of our ecosystems means investing in the health of our communities. 
Biosecurity measures, ecological restoration, and the elimination of illegal practices are fundamental to protecting biodiversity, public health, and people’s livelihoods. 

Coordinated action today can prevent larger crises tomorrow. 

5greatforestsinitiative.org