New World Screwworm in Cattle: Symptoms & Treatment | FBN

New World screwworm (NWS), caused by the larvae of the fly Cochliomyia hominivorax, is no longer a hypothetical threat for U.S. producers — it's an active outbreak. As of June 22, 2026, USDA has confirmed 15 cases in the United States: 14 in Texas and 1 in New Mexico. The first U.S. detection in nearly 60 years was confirmed June 3, 2026, in a three-week-old calf in Zavala County, Texas.

Producers deal with flies every year. NWS is different. Instead of simply irritating cattle, the larvae feed on living tissue, turning a routine wound — from branding, castration, ear tagging, or injury — into a serious, potentially fatal animal health emergency. Left untreated, infestations cause severe tissue damage, secondary infection, and death.

The U.S. eradicated NWS in 1966 through a sterile-fly program. An outbreak that began moving north through Central America and Mexico in 2023 has now reached Texas and New Mexico, prompting active surveillance, quarantine zones, and a coordinated USDA-state response.

Current Situation

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