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Deadly Screwworm Parasite Found in U.S. Threatens Cattle Herd
USDA Says Food Supply Is Safe
Key Takeaways:
- The USDA confirmed June 3 a case of New World screwworm in a calf in South Texas, the first U.S. detection in nearly a decade.
- The parasite threatens an already tight U.S. cattle supply, raising concerns about livestock losses and high beef prices, though officials said the food supply remains safe.
- Authorities imposed quarantines, movement controls and sterile fly releases to contain the outbreak, while officials said broader escalation plans are ready if cases spread.
A deadly cattle parasite was confirmed in the U.S. for the first time in nearly a decade, posing the latest threat to a U.S. herd already at its lowest level in 75 years.
The U.S. Department of Agriculture confirmed late June 3 that a suspected case from South Texas tested positive for the New World screwworm. The affected animal, a 3-week-old calf in Zavala County, is the only case that the agency is tracking right now, Agriculture Secretary Brooke Rollins said on a call with reporters.
The agency is implementing quarantines, movement controls and surveillance in a 12-mile zone around the detection, and has also expedited the release of sterile flies to prevent the pest’s spread. Zavala County, while it is not situated within the main cattle production areas of Texas, still has a prominent livestock industry and was estimated in 2022 to contain more than 38,000 cattle.
There is “no reason to believe” that this will result in an establishment of the pest in the U.S., Rollins said. The USDA also said the food supply is safe as screwworm does not infest meat or other food sources.
Still, the detection of the parasite comes at a dire time for the U.S. beef and cattle industry, with a smaller herd having already sent consumer prices to record highs.
Shares of Tyson Foods Inc. and JBS NV were higher in premarket trading June 4, after slumping a day earlier on reports of the possible infection, which at the time was unconfirmed. Feeder and live cattle futures in Chicago both fell June 3.
As expected, @USDA_APHIS confirmed the detection of a New World Screwworm (NWS) fly in a 3 week old bovine in Zavala County, Texas. @USDA and Texas Animal Health @TAHC officials are taking immediate action to contain and eradicate NWS from the area.
For more… https://t.co/GJkUJl0XEI — Secretary Brooke Rollins (@SecRollins) June 4, 2026
The primary risk is presently to livestock, not to meatpackers or consumers, said Corbitt Wall, a livestock market analyst at DV Auction, adding that most calves are still on pasture at this time of the year and aren’t being sold.
While the screwworm’s detection should be supportive to cattle prices because it threatens supply, it also gives the consumer “pause whenever they reach into that meat case,” Wall said. “It’s always a downer. That’s one reason that we’re seeing it as a negative.”
The confirmed case “should not be cause for panic, but rather time for the full deployment of the next phase of the whole-of-government response USDA has been planning for months,” Senate and House Agriculture Committee Chairmen John Boozman and GT Thompson said in a statement.
The U.S. has been trying to contain the spread of the pest, which can kill an animal within days, as cases across the Mexican border posed a threat. The USDA paused imports of live Mexican cattle and built new facilities to disperse sterile flies. Still, the number of cases has recently accelerated in Mexico, with the closest detection in a goat about 25 miles away from the U.S. border, according to the USDA.
Image
An adult New World screwworm fly. (Denise Bonilla/U.S. Department of Agriculture via AP)
The screwworm’s presence in Mexico and the ensuing halt to the live cattle trade has exacerbated the supply tightness for U.S. meatpackers, who have been facing operational losses as they pay for fewer and costlier animals. That shortage has also sent consumer beef prices to all-time highs, challenging President Donald Trump’s promise to ease grocery prices.
The U.S. Meat Export Federation said it doesn’t expect any disruptions to U.S. beef exports, but will “monitor the situation carefully for any trading partner actions that could interrupt beef trade.”
The screwworm was last detected in the U.S. in 2016 among deer in the Florida Keys, before being eradicated by early 2017, according to the USDA. The most recent occurrence involving infected cattle came in a 1976 outbreak that impacted Texas’s economy by as much as $375 million in non-inflation-adjusted dollars, the agency said.
While the risk to humans is low, the U.S. confirmed one case of the parasite last year in an individual who had traveled from Central America.
The USDA in its previously prepared plan said in the event of a localized outbreak, it would initiate movement restrictions for animals in and out of an infested zone. A larger outbreak spanning multiple counties would require the use of animal drugs, which the U.S. Food and Drug Administration has already issued emergency use authorization for. Rollins said on the call with reporters that a plane is already headed to South Texas with a “lot of that treatment stockpile.”
Shares of Elanco Animal Health Inc., which makes one of those treatments, settled at the highest in nearly a month on June 3, and Zoetis Inc. shares also rose. Both companies extended those gains in early trading June 4.
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The companies stand to benefit if the outbreak becomes more severe as a potential lowering of U.S. cattle inventory would be “more than offset by increased spending of livestock drugs,” KeyBanc Capital Markets analysts Steve Dechert and Scott Schoenhaus wrote in a note.
Tyson ranks No. 9 on the Transport Topics Top 100 list of the largest private carriers in North America and No. 1 among agriculture/food processing carriers. JBS ranks No. 86 on the TT Private 100 and No. 12 on the agriculture/food list.
