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By Alice Gibbs
Senior Reporter
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Federal officials have confirmed 116 cases of New World screwworm across the Southwest, up nearly 55 percent from the total recorded a week earlier on October 29.
The latest U.S. Department of Agriculture data shows 56 active cases and 60 inactive cases. An inactive designation means mitigation is no longer required for the individual animal and does not necessarily mean the surrounding area is free of the parasite.
Of these, 64 of the 116 cases were confirmed in the past 30 days.
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Recent detections include cattle in Hudspeth and Mitchell counties, Texas, a horse in Greenlee, Arizona and more cattle in Eddy and Otero counties, New Mexico. There is also a reported case in a domestic dog in Sierra county, New Mexico.
Cases have also been detected in fly traps. These findings are tracked separately from animal cases but provide additional evidence of the parasite's presence in the region.
What Is New World Screwworm?
New World screwworm is a parasitic fly whose larvae infest the wounds of living, warm-blooded animals, feeding on living tissue. It can affect livestock, wildlife, pets and, more rarely, people.
The USDA describes it as a serious threat to livestock and wildlife, although it currently assesses the risk to people in the United States as very low and says the outbreak is not a food-safety issue.
Newsweek reached out to the USDA via email for comment. Earlier this year, the department told Newsweek: “USDA is responding aggressively to the current outbreak through a fully coordinated effort that includes trapping, animal inspections, wildlife surveillance, sterile insect releases, and extensive public outreach. Together, these tools isolate cases and break the pest’s lifecycle to help prevent further spread.”
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How Screwworm Returned After U.S. Eradication
New World screwworm was considered eradicated from the U.S. in 1966 following a campaign using the sterile insect technique, in which large numbers of sterile male screwworm flies were released. When wild females mated with the sterile males, they produced no viable offspring, progressively suppressing the population. The U.S. and partner countries subsequently pushed established screwworm populations south through Mexico and Central America.
In 2023, Panama and Costa Rica identified a renewed outbreak. The parasite subsequently spread through every country in Central America and into Mexico, areas where it had previously been controlled. By October 2026, countries in Central America and Mexico had reported more than 209,400 animal cases and 2,850 human cases, according to the CDC. The current outbreak followed, with the first case confirmed on June 3, 2026.
How the U.S. Is Fighting the Outbreak
Today, the USDA strategy documents emphasize three core pillars: restricting animal movement, strengthening surveillance systems and deploying sterile insect technology at scale.
“If a domestic detection occurs, USDA will act swiftly to implement a response. Isolating the incident, deploying resources, and initiating surveillance,” the agency said in its preparedness framework.
The USDA has also announced around $105 million in funding for projects aimed at improving detection, control and eradication tools.
Can Screwworm Spread to Humans or Pets?
Screwworm infestations primarily affect livestock, but they can also impact pets, wildlife and, in rare cases, humans.
No locally acquired human cases have been reported in the United States during the current outbreak, according to the CDC.
The FDA has issued emergency authorizations for antiparasitic drugs for animals, as demand increases in affected areas, though cases in pets do remain rare.
"Currently, most dogs in the U.S. are at low risk of NWS exposure because confirmed cases of NWS are in a limited geographic region. However, dogs that live in, travel to, or return from areas where NWS infestations have been identified by state or federal animal health officials, as well as certain countries south of the U.S. border, should be closely monitored for signs of infestation, such as visible maggots or foul odors in wounds or body openings," the FDA said in a statement this week.
Contact Newsweek editors on this story: Rebecca Flood and Cristina Diciu.
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