Caribbean & Central America - October 2025

At the end of August, Belize, Costa Rica, El Salvador, Guatemala, Honduras, Mexico, and Panama joined forces in Panama City to try and halt the spread of New World screwworm (NWS), which occurs when NWS fly larvae (Cochliomyia hominivorax) infest the flesh of living mammals – primarily cattle but also other domestic and wild species, including human beings. Eradicated from Central America in the early 2000s, the disease re-emerged in Panama in 2023, and has since been reported in the rest of the sub-region with “direct repercussions on food safety, the rural economy and community well-being”, according to the Inter-American Institute for Cooperation on Agriculture (IICA), which hosted the event.

According to an IICA statement, for the first time, on 28 August ministries of agriculture and health, the private sector, and technical specialists from the IICA, the Panama-US Commission for the Eradication and Prevention of Screwworm (Copeg), and US Centers for Disease Control and Prevention (CDC) in Central America came together to establish “a pioneering model of intersectoral collaboration for animal health and public health”.

The event is the latest sign of efforts to control the outbreak after NWS detections in Panama exploded in 2023 from an average of 25 cases per year to over 6,500 cases in one year. Until June 2023, Panama was considered the biological barrier against NWS for the rest of Central and North America. In 1998 Copeg, an international US-Panama mission for the control of NWS, began eradication efforts in Panama through the sterile insect technique. This involves the rearing and release of sterile male flies which, when mated with wild females, produce no offspring, thereby reducing the fly population in infested areas. In 2006 a sterile fly production plant was inaugurated in the town of Pacora, Panamá province, which dispersed flies from Bayano Lake, a reservoir in Panamá province, to 20 nautical miles into Colombia.

A 5 September article by US-based American Society for Microbiology, a professional organisation for scientists who study viruses, highlights that the resurgence in Panama of the disease occurred when “the flies suddenly overpowered the insect barrier and the difficult terrain of the Darien Gap at the southern tip of Panama.” It states that the exact cause of this breach is unclear but is most likely due to multiple factors, including interruptions in the production of sterile flies as a result of the coronavirus (Covid-19) pandemic, illegal cattle imports, “as well as the challenges involved in surveillance of the Gap’s difficult geography”.

With Costa Rica identifying its first case of NWS in 2023, and Nicaragua, Honduras, Guatemala, Mexico, and El Salvador following suit in 2024, national emergencies have been declared across the sub-region in response to NWS. A 14 August report by Italy-headquartered news agency Inter Press Service (IPS) cites figures from the El Salvador-based regional agricultural health organisation (Oirsa) as estimating that as of the start of July, some 99,000 NWS cases had been registered in Central America, mainly in cattle.

As well as the use of sterile flies, efforts to curb the spread of NWS include strategies of prevention, control, and training. The government of the US, where the first human case of NWS in decades was registered on 4 August in a person who had travelled from El Salvador, has also stepped up its response. In June, US Secretary of Agriculture Brooke Rollins announced a five-pronged plan to eliminate NWS. Among other things, this includes US$21m in funds to renovate an existing fruit fly production facility in Mexico’s Metapa de Domínguez municipality, Chiapas state, which will provide an additional 60-100m sterile flies a week to stop the spread, on top of the more than 100m already produced in Panama.  However, Oirsa’s regional NWS coordinator Marcela Marchelli has been cited by the regional media as saying that it could take between 10 and 12 years to eradicate the pest in Central America.

Cost

In October 2024 Central American business magazine Revista Estrategia y Negocios cited José Loaiza, a researcher at Panama’s state university, Universidad de Panamá, as citing scientific studies which estimate that annual economic losses from NWS could total over US$150m in Central America.

Cattle trafficking

A November 2024 report by US non-profit Wildlife Conservation Society (WCS) highlights studies by specialists at Mexico’s Universidad Nacional Autónoma de México (Unam) which suggest that cattle smuggling may be accelerating the spread of NWS.

It cites Alejandro Zaldivar Gómez, a Unam researcher, as saying that the findings of a new report indicate that NWS has been spreading across Central America at an average rate of 1.6km per day. According to Zaldivar Gómez, this spread rate “allows us to project its geographic reach over the short and medium term, offering critical data for designing surveillance and control strategies in high-risk areas”. The WCS report cites Zaldivar Gómez as saying that in recent months, “the spread has accelerated significantly”, with new outbreaks reported up to 300km away from previous infection points. It says that “these long-distance movements provide further evidence that illegal cattle trafficking is likely fuelling the fly’s expansion through Central America”, noting that this claim has been backed by regional health authorities. It highlights official inspection documents from Honduras and Nicaragua, published by the World Animal Health Information System (Wahis), which collects and publishes information gathered by individual countries’ veterinary services, which outline how the parasite has entered these countries via smuggled cattle.