The confirmation of a case of the New World screwworm (NWS) in Texas set off alarm bells across the United States, marking the return of a pest that had been eradicated from the country more than half a century ago. The discovery comes at a particularly sensitive time for the livestock industry, which is facing the smallest cattle herd in 75 years and record-high beef prices, raising concerns about the potential economic consequences of a spread of the parasite.
The Department of Agriculture (USDA) confirmed that the larvae were detected in a three-week-old calf in Zavala County, in southern Texas near the border with Mexico. This is the first case recorded in the state since 1966 and, so far, the only one confirmed on U.S. soil. The detection came after months of warnings from federal authorities, state officials, and livestock organizations about the pest’s advance through Mexico toward the border.
Upon confirmation of the case, the USDA activated a response plan that includes a quarantine zone of approximately 19.3 kilometers (12 miles) around the site where the calf was found, restrictions on the movement of livestock and other warm-blooded animals, as well as increased insect surveillance and trapping efforts. Authorities also announced the deployment of a joint command team with the Texas Animal Health Commission to coordinate containment efforts.
Agriculture Secretary Brooke Rollins sought to reassure producers and consumers by stating that there are no signs of a widespread infestation. “There is no reason to believe this incursion will result in the establishment of the pest in our country,” she said. Rollins emphasized that the case detected in Texas is, for now, an isolated incident.
The New World screwworm is not transmitted directly between animals. The threat comes from the fly that lays its eggs in open wounds or body cavities. When the eggs hatch, the larvae penetrate the living tissue and begin to feed on it, causing severe lesions, infections, and, in the most serious cases, the death of the affected animal. Although infections in humans are rare, health authorities acknowledge that they can occur.
To combat the spread of the parasite, the federal government has once again turned to a strategy that proved decisive during the eradication campaigns of the last century: the release of sterile male flies. Because females typically mate only once in their lifetime, the species’ reproduction declines when they mate with males incapable of producing offspring.
“USDA invested heavily in the tools needed to eliminate NWS ever since cases started increasing in Central America and Mexico. The United States has defeated this pest before, and we will do it again,” said Dudley Hoskins, the department’s undersecretary for Marketing and Regulatory Programs.
The federal government had already stepped up its preparations in recent months in response to the pest’s steady spread through Central America and Mexico. In March, the USDA announced the construction of a new facility for producing sterile flies at Moore Air Force Base in Edinburg, Texas, as part of efforts to strengthen the response to a potential arrival of the insect on U.S. soil.
However, some state officials believe that federal measures were insufficient to contain the spread of the pest. Texas Agriculture Commissioner Sid Miller criticized the strategy pursued so far by the federal government and called for a more aggressive mobilization of resources.
“For months, the screwworm has advanced rapidly through Mexico in spite of the USDA’s existing gameplan,” Miller said in a statement. The official added that “even though billions of sterile flies have been dispersed by USDA, the screwworm has still advanced over 1,100 miles from southern Mexico to Texas, and USDA has missed an important component. Now that it appears the first screwworm has arrived in Texas, the consequences of that decision are now staring us in the face.”
Miller also urged President Donald Trump’s administration to expand the use of the Screwworm Adult Suppression System (SWASS), a method that combines attractants, baits, and insecticides to reduce adult fly populations prior to the release of sterile insects.
Beyond the health risk to livestock, concerns center on the potential economic repercussions. The United States is experiencing a period of limited cattle supply following years of drought, high feed costs, and a demand for beef that has remained strong despite rising prices. As a result, retail beef prices are at historic highs.
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