New World Screwworm Detected in Second Cow in Texas
The U.S. Department of Agriculture (USDA) has confirmed the presence of the New World screwworm in a second cow in Texas, marking a significant development in the ongoing efforts to contain this parasitic infestation. The detection occurred in a one-month-old calf in Zavala County, approximately 5.6 miles from where the first case was identified earlier in the week.
“With our partners in Texas, we are responding with speed and strength,” the agency stated in a social media post. This response comes as officials work to prevent further spread of the pest, which poses a serious threat to livestock and, although rare, can affect humans.
Earlier in the week, the USDA confirmed the first case of New World screwworm in a three-week-old cow, also in Zavala County. According to the agency, larvae were found in the animal’s umbilical area, and no additional cases have been reported in the U.S. so far.
Secretary of Agriculture Brooke Rollins emphasized that “USDA and Texas Animal Health officials are taking immediate action to contain and eradicate NWS from the area.” The Department of Agriculture has formed a unified Incident Command Team with the Texas Animal Health Commission and is deploying personnel to the affected region.
The USDA warned that the parasitic fly may have entered the mainland U.S. after migrating north from countries in Central America and Mexico, where an outbreak has been affecting livestock since at least 2022.
Understanding the Threat of New World Screwworm
New World screwworm (NWS) is a species of parasitic flies that feed on live tissue, typically targeting livestock. While human infections are rare, U.S. health officials have indicated that the risk to public health remains very low. However, the potential for the infestation to devastate the cattle industry is a major concern.
The name “screwworm” refers to the way in which maggots screw themselves into the tissue of animals using their sharp mouth hooks, causing extensive damage and often leading to death.
In August 2025, the U.S. reported its first human case of NWS in an international traveler. The individual recovered without any evidence of further spread.
For decades, the U.S. successfully eradicated screwworm in livestock through a technique involving the release of sterilized male flies to mate with females, eventually reducing the population to zero. Since the eradication in 1966, isolated outbreaks have occurred in the American Southwest and the Florida Keys.
People who travel to outbreak areas, spend time among livestock, sleep outdoors, or have open wounds are at greater risk of becoming infested with screwworm, according to the Centers for Disease Control and Prevention.
Measures Being Taken to Contain the Outbreak
In response to the recent detections, the Department of Agriculture has implemented several actions. These include establishing a 12.5-mile “infested zone” around the detection area, along with quarantines, movement controls, and increased surveillance.
The department also plans to expedite the targeted release of sterile New World screwworm flies from the ground, a tactic that was used successfully during the 2016 outbreak in the Florida Keys. This effort will complement the current release of 4 million sterile flies per week by air in the area.
Earlier this week, Secretary Rollins assured Americans that the “food supply is 100% safe” despite potential disruptions to the U.S. cattle supply due to the NWS infestation. Officials remain focused on containing the outbreak and preventing further spread to protect both livestock and public health.
