SHIC/AASV Webinar on New World Screwworm Provides Valuable Perspective on Threat

The Swine Health Information Center in collaboration with the American Association of Swine Veterinarians hosted a webinar on June 13, 2025, entitled “Emerging Risk of New World Screwworm (NWS) and Efforts to Prevent Re-introduction into the US.” The webinar had 727 registrants from around the globe, 529 attended live from 18 countries, and it is now available for on demand viewing. The webinar provided the latest information on NWS, including an overview of the parasite, the fly lifecycle, clinical signs of infestation, impact to producers, Texas prevention and preparedness activities, and a status update for NWS in Mexico. To date, NWS has not been identified in the US since it was eradicated from the Florida Keys in 2017.  

The identification of NWS in Oaxaca and Veracruz, within 700 miles from the US/Mexico border, raises concern about this potential emerging threat to swine health. Increasing awareness and understanding of this parasitic fly as well as prevention and mitigation steps for NWS infestation help US pork producers protect their herd health.  

Presenters offering their expertise included: 

Cody Egnor, DVM, veterinary medical officer, United States Department of Agriculture  

Nancy Adams, DVM, Texas Animal Health Commission Epidemiology Department 

Kathy Simmons, DVM, chief veterinarian, National Cattlemen’s Beef Association  

Moisés Vargas-Terán, DVM, international animal health expert consultant for OMSA, FAO, IAEA, WHO, and the IDB  

The myiasis caused by New World Screwworm, Cochliomyia hominivorax, is a parasitic fly whose larvae infest and feed on the living tissue of warm-blooded animals, including humans. In his presentation, Dr. Egnor emphasized that, unlike other flies, NWS maggots feed exclusively on living tissue. Female flies lay 200-300 eggs around wounds or natural orifices like the eyes, ears, nose, anus, umbilicus, and genitalia. These eggs hatch within 12 to 24 hours, and the emerging larvae burrow deep into the flesh, tearing at tissue with hook-like mouth parts, leading to severe inflammation and secondary infections. The entire life cycle can be as short as 21 days in tropical climates.