US launches multi-pronged effort to control flesh-eating screwworm outbreak
US agriculture and health officials have initiated a plan to combat the New World Screwworm, a parasitic fly detected in the US for the first time since 1966. The outbreak, identified in southern Texas near the Mexico border, poses a threat to livestock and could impact beef markets. The response includes releasing genetically sterile flies, establishing containment zones, and deploying sniffer dogs to detect the insects.
Why this matters
The screwworm parasite causes severe damage by laying eggs in open wounds of warm-blooded animals, including cattle and humans. The larvae burrow into living flesh, potentially killing the host if untreated. While the risk to humans is low, an outbreak could significantly disrupt the cattle industry and beef supply in the US. Controlling the spread is critical to protecting livestock health and economic stability in affected regions.
Key developments in the response
- The first US case in over 60 years was found in a three-week-old calf in La Pryor, Texas, near the southern border.
- A 20-kilometer-wide control zone has been established around the infection site, with quarantines, movement controls, and surveillance enforced by the USDA.
- Hundreds of millions of sterile screwworm flies are planned for release to reduce the population, using the Sterile Insect Technique where sterilized males mate with wild females, preventing viable eggs.
- Currently, production capacity for sterile flies is about 100 million per week, below the estimated 600 million needed weekly to effectively combat the outbreak.
- Since February, officials have released approximately 8 million sterile flies weekly, both by ground and air.
- Specialized sniffer dogs, known as the “Beagle Brigade,” are being used at border points to detect screwworm presence in livestock and pets.
Background on screwworm control efforts
The screwworm was eradicated from the US decades ago through extensive use of sterile fly releases, particularly in the 1970s when 500 to 700 million sterile flies were released weekly across Central America. However, in recent years, the pest has resurged, spreading northward from Panama through Central America and Mexico, reaching the US border by 2024.
Efforts to track and control screwworms in Central America were previously supported by the US Agency for International Development (USAID), but that program was eliminated, drawing criticism for slowing response times.
Challenges and concerns
- Experts warn that current sterile fly production is insufficient to immediately halt the outbreak.
- Some cattle ranchers and officials criticize the federal response as slow and inadequate.
- There is debate over the use of insecticide traps, which officials say are ineffective and pose environmental risks.
- Officials attribute the pest’s northward spread partly to cross-border movement of livestock and pets, and climate change potentially expanding the insect’s range.
- Ranchers are urged to cover wounds on animals and report any signs of screwworm infestation promptly.
Health and safety considerations
The screwworm larvae feed on living flesh, but the threat to humans remains low. The US Centers for Disease Control and Prevention (CDC) reported over 2,000 human cases in the region recently, though fatalities are rare with proper treatment. Vigilance in livestock management and public awareness are key to preventing further spread.
Recommended reading
For more context, see related Peack News coverage and explainers linked below.
