A case of New World screwworm (NWS) was recently confirmed in a 30-month-old pig in the Mexican state of Veracruz. This state currently has 125 active cases of NWS and 1,963 total cases reported. No other information was reported from USDA when the case was listed on the NWS website Jan. 9.
As the number of cases continue to rise and inch closer to the U.S. border, livestock producers need to be on alert. NWS poses a real threat to rural America, says Texas beef producer Donnell Brown.
“Fortunately, we made it to winter without a major screwworm infestation in the United States,” he says in a recent article on PorkBusiness.com. “However, as temperatures rise this spring and fly season begins again, I am deeply concerned that we could see an outbreak with devastating consequences for livestock and wildlife.”
Lizeth Olivarez doesn’t know if people will have the stomach to deal with NWS. She’s a sixth-generation rancher who runs cattle in the U.S. and in Mexico at Las bendiciones Ranch in Realitos, Texas, and Rancho El Cuellareno in Guerrero, Mexico. Though she hasn’t experienced it herself, she has grown up hearing story after story about NWS from both her grandfather and father who dealt with NWS when the deadly fly struck in the 1960s.
A Threat to the U.S. Swine Industry, Too
Though only three cases have been reported in swine since July 4, 2025, the potential for infection is there, especially for domestic pigs raised outdoors and wild pigs.
Megan Niederwerder, executive director of the Swine Health Information Center (SHIC), says it’s important to remember this is not just a cattle disease; it impacts other livestock species and humans as well.
“It’s really important to stay vigilant as we think about increasing awareness and understanding of what the fly looks like,” Niederwerder says.
Pork producers should be aware of the disease and be watchful for suspect clinical signs of myiasis (fly infestation), adds Lisa Becton, DVM, associate director of SHIC.
“Flies lay eggs in live tissue of a wound — even a wound as small as an injection site or a tick bite,” Becton says.
Producers should continue to perform normal daily animal monitoring/observations and identify suspect wounds that do not heal, have drainage or smell bad, she explains.
“Prompt treatment of scratches or other wounds with approved topical wound spray is important for everyday management of animal health/welfare,” Becton says. “Monitor other susceptible animals like newborn piglets for signs of myiasis. If lesions are suspected, contact your state veterinarian and your herd veterinarian.”
The most important thing U.S. pork producers need to know is that NWS is not currently in the U.S., Becton says. However, if you suspect an animal is affected, contact your herd and state veterinarian immediately for further investigation.
Current information related to NWS is available on the USDA Animal and Plant Health Inspection Service website, including a current situation map and table showing cases within 400 miles of the U.S.
