Ames, Iowa – The Council for Agricultural Science and Technology (CAST) hosted a webinar on December 9, 2025, addressing the New World Screwworm threat from a One Health perspective. The session brought together experts from animal health, public health, veterinary medicine, and federal regulatory agencies to discuss prevention, detection, and treatment strategies.
One Health Approach to a Persistent Threat
Julia Herman, Beef Cattle Specialist Veterinarian with the National Cattlemen’s Beef Association and webinar moderator, explained that New World Screwworm exemplifies a One Health issue affecting animals, people, and the environment. The parasite can impact livestock producers, wildlife managers, pet owners, community members, and regulatory officials.
Understanding the Biology and Threat
Dr. Sonja Swiger, Professor and Extension Entomologist with Texas A&M AgriLife Extension, provided background on Cochliomyia hominivorax, the scientific name for New World Screwworm, which translates to “man-eater.” The fly infests the living tissue of warm-blooded animals, causing a condition called myiasis. If untreated, infestations can result in animal death.
The species prefers tropical or subtropical temperatures between 60 and 90°F and historically inhabited the southern half of North America. Dr. Swiger noted that the fly was successfully eradicated from the United States in the 1950s-1960s through a sterile insect technique program, which continues to maintain a barrier in Panama.
Current Situation and Response
Chris Needham, Deputy Director for the APHIS New World Screwworm Directorate, discussed the current outbreak in southern Mexico and federal response efforts. He outlined a two-track approach: continuing proven methods, such as the sterile insect technique, while exploring new technologies and treatments.
The USDA has conditionally approved products from Merck and Zoetis specifically labeled for New World Screwworm treatment in livestock. Dr. Lynne Acebey from the American Veterinary Medical Association explained that these approvals provide veterinarians with additional treatment tools, particularly important given the specific regulations governing medications for food animals.
Human Health Considerations
Dr. Megin Nichols, Director of the CDC’s National Center for Emerging and Zoonotic Infectious Diseases, addressed human health concerns. She emphasized that people with suspected screwworm infestations should seek immediate medical treatment. The CDC follows cases through physician reporting and works with state health departments to track potential exposures.
FSIS has posted Q&A resources about the slaughter of livestock affected with New World Screwworm, and the FDA provides information on conditionally approved products.
Key Recommendations
The panelists emphasized several critical points:
Prevention is Primary: Biosecurity measures, wound care, and surveillance form the foundation of protection. Integrated pest management requires multiple approaches beyond treatment drugs alone.
Report Suspicions Immediately: Contact state animal health officials or state veterinarians if New World Screwworm is suspected. For human health concerns, seek medical treatment and follow CDC guidelines.
Early Detection is Critical: Regular examination of animals and people in affected areas enables faster treatment and prevents spread.
Veterinary Consultation: Work with veterinarians to ensure approved medicines are used appropriately and responsibly.
Partnership is Essential: Cooperation among producers, veterinarians, universities, federal regulators, and community members is necessary for an effective response.
Resources
Information is available at:
- screwworm.gov (USDA APHIS)
- wwwwww.avma.org (American Veterinary Medical Association)
