New World Screwworm (Cochliomyia hominivorax) a parasitic fly whose larvae feed on the living flesh of warm-blooded animals, including livestock, pets, wildlife, and occasionally people. Unlike other flies that feed on dead tissue, screwworm larvae can only develop in living flesh, making infestations rapidly destructive. Female flies lay their eggs in existing wounds or mucous membranes — around the eyes, mouth, or udder — and the hatching larvae cause a condition called myiasis, which leads to serious injury, infection, and death if left untreated. Secondary bacterial infections attract additional egg-laying females, creating a self-reinforcing cycle that rapidly worsens the damage.

The economic consequences of screwworm infestations are severe. Farmers face costly and labor-intensive treatment regimens, ongoing prevention measures, and disruptions to routine animal management practices. Smallholder farmers are especially vulnerable, as even minor outbreaks can threaten household income and food security. At a larger scale, outbreaks can cause devastating livestock losses and trigger trade restrictions and quarantines that compound the economic damage across entire regions

Although the screwworm was successfully eradicated from North and Central America for many years, it is currently endemic in South America and parts of the Caribbean. Over the past five years, the parasite has resurged across Central America and spread northward into Mexico, re-establishing itself across much of its original range. The primary eradication tool is the sterile insect technique (SIT), an environmentally friendly method that uses radiation to produce sterile male flies. SIT must be combined with wound management, close monitoring, and robust surveillance to be effective.

FAO's role

Today, the Food and Agriculture Organization (FAO) plays a central role in prevention, detection, and control efforts across affected countries, working alongside partners such as World Organisation for Animal Health (WOAH), International Atomic Energy Agency (IAEA), and national veterinary services to implement science-based strategies, strengthen surveillance systems, and build local capacity to manage this ongoing threat.

• Global coordination and policy guidance: In collaboration with the World Organisation for Animal Health (WOAH) under the Global Framework for Transboundary Animal Diseases (GF-TADs), FAO provides policy guidance and technical support to governments, helping countries strengthen NWS surveillance, prevention, and biosecurity measures while ensuring a coordinated international response.
• Regional and national coordination: Working with the Panama-United States Commission for the Eradication and Prevention of Screwworm Infestation in Livestock (COPEG) and national veterinary services across Central America, FAO is helping to strengthen prevention and control efforts in countries where New World Screwworm has re-emerged.
• Research and innovation: Through a joint programme with the International Atomic Energy Agency (IAEA) of Nuclear Techniques in Food and Agriculture, FAO provides scientific support for sterile insect technique (SIT) operations.
• Early warning and surveillance: EMPRES-i+ provides readily accessible data on where the disease has occurred, giving national-level authorities an improved understanding of New World Screwworm spread patterns and potential border threats. These early warning systems support centralizing information and help to ensure coordinated information sharing across borders.
• Research and innovation: FAO supports evidence-based decision-support tools, diagnostic tools, and studies on disease transmission. By advancing scientific research and innovative solutions, FAO helps countries strengthen their long-term ASF prevention and control strategies.
• Capacity building and knowledge sharing: FAO operates in seven countries in Central America (Mexico, Guatemala, Belize, Honduras, El Salvador, Costa Rica and Panama), all of which have recently reported active cases of New World Screwworm. On-the-ground operations offer training for veterinary services to strengthen biosecurity and prevent further spread. Workshops in Good Emergency Management Practices (GEMP) have been conducted in Guatemala, El Salvador, and Honduras.
• Emergency response and risk management: In response to outbreaks, FAO provides emergency technical assistance to strengthen surveillance, prevention, and epidemiologic capacities for New World Screwworm.

Frequently asked questions

Key questions and answers on the New World Screwworm, including its spread, risks to animals and humans, and measures for prevention and control.