Livestock Owners Advised to Monitor for Screwworm Fly

By Blake Jackson

University of Kentucky’s Martin-Gatton College of Agriculture, Food and Environment, alongside state partners, is urging livestock owners and veterinarians to remain vigilant as New World screwworm (NWS) activity persists in parts of Central America and Mexico.

No cases have been reported in the U.S., and Kentucky herds remain unaffected, but experts stress the importance of preparedness.

The NWS fly is an obligate parasite whose larvae burrow into living tissue, causing severe lesions, secondary infections, and even death if untreated. While cattle are most susceptible, sheep, goats, horses, companion animals, wildlife, and humans can also be affected.

Even minor wounds or natural openings like the nose, eyes, ears, anus, or genitalia can attract egg-laying females. Infested wounds enlarge quickly and may emit a strong odor.

“NWS is an old foe,” said Hannah Tiffin, UK Department of Entomology assistant professor. “It used to affect animals, especially cattle in Texas and throughout the South but thanks to the advent of SIT, it was mostly eradicated from the US in the 1960s.”

Kentucky agencies including the Department for Public Health, Department of Agriculture, and Department of Fish and Wildlife, along with veterinarians and university researchers, meet weekly to monitor vector-borne threats.

“Cattle are large animals that may go some time between health checks,” Tiffin said. “Flies have ample time to lay eggs and allow the maggots to cause gaping wounds in several animals before the infestation is noticed. This is why knowing what to look for is so important.”

Producers should inspect animals regularly for deep, rapidly enlarging wounds, foul odor, persistent irritation, or head-shaking, paying particular attention to newborns’ navels and natural openings.

Suspected cases should be reported to the state veterinarian at (502) 573-0282 or USDA-APHIS Veterinary Services at (502) 848-2040.

While human infection is rare, vigilance remains essential. Kathleen Winter, associate professor in UK’s College of Public Health, said, “Although the current risk to the general public is very low, there is the concern that people who travel to countries where this fly is either endemic or becoming more common are at increased risk.”

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