New World screwworm (NWS) is a serious pest of livestock and wildlife. USDA is leading a coordinated One Health response to combat NWS. This is not a food safety issue—the U.S. food supply remains safe. The current risk to animals and people in the United States is very low.
Animal Health Officials Working Quickly to Protect U.S. Livestock and Wildlife
WASHINGTON, D.C., June 3, 2026—The U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) confirmed the detection of a New World screwworm (NWS) in a bovine in Zavala County, Texas. NWS is a serious pest that affects livestock, pets, wildlife, and less commonly, people and birds. NWS larvae (maggots) burrow into the flesh of living animals, causing serious damage to livestock and economic losses.
The affected animal is a 3-week-old calf and larvae were identified in its umbilical area.
To date, there have been no further detections.
“All models showed New World Screwworm entering the country in 2025; however, thanks to the hard work across the entire Trump administration and our industry, state, and local partners, we were able to buy time for this moment. Protecting our livestock industry is a national security issue of the utmost importance, and USDA is wasting no time in taking action,” said Dudley Hoskins, Under Secretary for Marketing and Regulatory Programs. “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.”
USDA and Texas officials are taking immediate action to contain and eradicate NWS from the United States, following the strategies and actions outlined in the NWS Response Playbook (884.59 KB).
The Facts About New World Screwworm (https://www.aphis.usda.gov/sites/default/files/nws-myth-busters.pdf)
New World screwworm (NWS, Cochliomyia hominivorax) is a serious pest that affects livestock, pets, wildlife, and, less commonly, people and birds. Adult screwworm flies are about the size of a common housefly or slightly larger. Their larvae feed on the living tissue of warmblooded animals. The U.S. Department of Agriculture (USDA) is leading an aggressive response to keep NWS out of the United States. Thanks to strong surveillance and rapid response programs, the current risk to animals and people in the United States remains very low. This factsheet addresses common myths and misconceptions about NWS.
MYTH: All maggot infestations (myiasis) are caused by NWS.
FACT: Myiasis is an infestation of fly larvae (maggots) in tissue. It occurs when flies lay eggs in wounds or body openings. Not all myiasis is caused by NWS. Other flies—such as botflies and blowflies—can also cause similar infestations. In some cases, animals may be infested with maggots from both NWS and other species of botflies or blowflies at the same time. Species identification by an entomologist is required to determine whether it is NWS. If you see suspicious wounds or maggots on animals, contact your veterinarian immediately. Animal health professionals should report suspected cases to the State animal health official and USDA Area Veterinarian in Charge. If you have symptoms of myiasis, contact your healthcare provider. Healthcare providers should report suspected cases to the local or State health department.
MYTH: NWS can spread from animals to people and person to person.
FACT: NWS is not contagious and does not spread directly from animals to people or from person to person. Screwworm infestations begin when a female fly lays eggs on a wound or body opening. Eggs hatch into larvae that burrow into the wound and feed on living tissue. After about 7 days of feeding, larvae drop to the ground, burrow into the soil, and pupate. The adult screwworm fly emerges from the soil after 7–54 days depending on temperature and humidity. Female flies mate after 3 days, while males can mate within 24 hours of maturation, and the cycle continues.
MYTH: If an animal is infested, the whole herd must be culled.
FACT: Culling will not be used to manage herds in which individual cattle or other livestock are infested with NWS. Instead, premises with suspected cases of NWS will be placed under a hold order and not allowed to move animals until they are examined for NWS. Livestock infested with NWS will be treated and quarantined until all wounds heal and there is no evidence of reinfestation after 21 days. In rare cases, euthanasia may be necessary for individual animals for humane reasons or in cases when treatment is not possible.
MYTH: Infested animals must be destroyed and cannot enter the food supply.
FACT: Animals that have recovered from NWS myiasis can enter the food supply if they meet all regulatory requirements, including release from on-farm quarantine and absence of residues, and they pass USDA’s Food Safety and Inspection Service (FSIS) inspection which ensures humane handling of animals and food safety requirements are met. FSIS inspection before and after slaughter will determine whether the entire carcass, or only unaffected parts, are passed for human food. Severely infested animals will not be allowed into food production. More information can be found at askFSIS.
MYTH: NWS could enter the food supply and infest people.
FACT: The U.S. food supply is safe. NWS is not a food safety issue. It spreads only when an NWS fly lays eggs in a wound, not through meat, poultry, or dairy products.
MYTH: One infested animal that crosses the border will result in a nationwide outbreak.
FACT: Mexico, with USDA leadership and support, has established a layered system of safeguards to ensure livestock moving north toward the U.S. border are free of screwworm. These safeguards include: • Enforcement of animal movement, inspection, and treatment protocols • Upgraded infrastructure at checkpoints • Modern electronic traceability systems systems
In the United States, USDA conducts intensive surveillance along the U.S.-Mexico border to detect screwworm should it reach the United States. USDA “tick riders”—mounted patrol inspectors who patrol the border—intercept and treat stray livestock for NWS.
MYTH: Coughing or other respiratory illness means an animal has NWS.
FACT: NWS does not cause respiratory illness or coughing. Instead, look for:
More information on New World Screwworm can be found at the links below:
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