Screwworm Can Infect People, Pets, And Livestock—What To Watch For

InnovationHealthcareScrewworm Can Infect People, Pets, And Livestock—What To Watch ForByJudy Stone,Senior Contributor.Forbes contributors publish independent expert analyses and insights. Dr. Judy Stone focuses her writing on infectious diseases.Follow AuthorJun 11, 2026, 08:00am EDTAn adult New World screwworm fly sits at rest in this undated photo. (Denise Bonilla/U.S. Department of Agriculture via AP)U.S. Department of AgricultureNew World screwworm was detected last week in cattle and a goat in Texas, as well as a dog in New Mexico. While the major focus has been on the impact this might have on beef prices, the parasite can also infect people and their pets. Here’s what to know.New World screwworm, Cochliomyia hominivorax, is caused by a parasitic fly that is attracted to wounds and body openings (like the nose, ears, eyes, mouth, or genitals). It lays 200-300 eggs there at a time, and when they hatch, the larvae (maggots) eat the live tissue. The female fly may lay up to 3,000 eggs before she dies. After the maggots feed for about a week, the larvae drop to the ground for the next part of their life cycle. They then emerge as adult flies, and the cycle repeats.The bites from screwworms can be quite painful and cause foul-smelling wounds, which attract more flies. Other symptoms include non-healing or bleeding wounds and feeling or seeing the maggots.NWS has been found to infect people and animals in South America and the Caribbean. Following an initial outbreak in Panama and Costa Rica in 2023, NWS has been moving northward through all of Central America and Mexico. Last year, the U.S. had a human case in Maryland in a traveler who had returned from El Salvador.The people at greatest risk are those who spend a lot of time outdoors in areas with livestock, which host the flies, and who have any open wound, even if small. People who are asleep or unable to keep flies away are particularly susceptible. Those with larger open sores, as from cancer or diabetes, are...