AABP Executive Director Dr. Fred Gingrich is joined by AABP member and Texas rancher Dr. Chris Womack to discuss the concerns about the New World Screwworm discovery in the southernmost state of Mexico. Womack discusses the history of this fly and an interesting story from his childhood of it being found on his father’s ranch in the mid-70s.  

New World Screwworm strikes live tissue in all mammals and can be a serious risk to newborn calves as well as adult animals. Flies are attracted to fresh wounds where they lay eggs and the larvae feed on this living tissue. The pest has been eradicated in the mainland U.S. since 1966 with a few sporadic outbreaks. The USDA has had a collaborative relationship with Panama to prevent the pest from migrating north; however, it was discovered in an adult cow in Chiapas, Mexico in late 2024. This resulted in a shutdown of all cattle and bison from Mexico to the United States. Each year the U.S. fed cattle industry imports 3-5% of our cattle inventory from Mexico.  

Treatment for infected cattle includes ivermectins and organophosphate dips. If the pest gets into wildlife, it will be very difficult to manage; therefore, control outside of the U.S. remains critical to the cattle industry. Control revolves around the release of male sterile flies into the infected areas so that females will not lay viable eggs. It is critical for all veterinarians to be vigilant, even if you are only treating small animals, because the risk of the pest coming in on a companion animal is also considerable.

Find out more information from the USDA at this link. Resources from the National Cattlemen’s Beef Association can be found here.