New World screwworm not a food safety threat, Kansas officials emphasize
Surveillance, treatment and controlling animal movement key state’s response plan
At a glance: Kansas animal health officials and scientists are stressing that a current outbreak of New World screwworm, a flesh-eating parasite affecting livestock and other animals, does not pose a food safety concern for consumers.
More information:
Cassandra Olds, 785-706-8599, colds@ksu.edu
Sara McReynolds, 785-564-6792, Sara.McReynolds@ks.gov
Related: Sound Living
June 29, 2026
By Pat Melgares, K-State Extension news service
MANHATTAN, Kan. — Kansas animal health officials and scientists are stressing that a current outbreak of New World screwworm, a flesh-eating parasite affecting livestock and other animals, does not pose a food safety concern for consumers.
“This is not a food safety concern, and that’s an important point we want everyone to understand,” said Dr. Sarah McReynolds, assistant animal health commissioner for the Kansas Department of Agriculture. “We are very concerned about it as an animal health risk, (but) it is not a food safety concern.”
Listen to Sarah McReynolds and Cassandra Olds speaking about New World screwworm and food safety on the weekly radio program, Sound Living
New World screwworm, a parasitic fly that caused hundreds of millions of dollars in damage in Texas in the 1960s and 1970s, had been considered eradicated from the United States for decades. The first case in the current outbreak was confirmed June 3 in a three-week-old calf in South Texas, which has since recovered.
On a recent webinar, McReynolds and Cassandra Olds, a Kansas State University veterinary entomologist, outlined what producers, veterinarians and the public need to know about the parasite — and repeatedly underscored that it is an animal health, not a food safety, issue.
Olds said the larval stage of the New World screwworm fly feeds on the living tissue of any warm-blooded animal, including cattle, wildlife and pets. After mating, a female fly lays “hundreds and hundreds of eggs” on an existing wound or moist body opening such as the umbilicus, eyes or other mucous membranes.
The eggs hatch quickly into maggots that burrow into healthy flesh, causing severe pain and tissue damage.
“You may have a straw-colored, sometimes slightly bloody fluid oozing out of the wound, and there’s often a very distinctive, putrid smell,” Olds said. “If you smell that on an animal that has a wound and maggots, it’s a good indication to call in the professionals.”
Olds noted that the parasite’s life cycle includes a pupal stage in the soil, and that Kansas’ climate provides an important natural barrier.
“Our climate is not really all that suitable for the New World screwworm,” she said. “This is not a fly that is tolerant to cold. Adults do not survive if air temperatures are below 20 degrees Fahrenheit, and once the maggot has dropped off into the ground, if your average daily temperatures are below 46 degrees, that maggot can’t move to the pupal stage and emerge out.
“For us here in Kansas, it has always been a summer concern. It will likely remain a summer concern. Every winter we are going to clear out.”
The United States declared the New World screwworm eradicated in 1966, after a large-scale effort that used monitoring, restrictions on animal movements and a technique that capitalizes on rearing flies in laboratories, sterilizing them, and releasing them in high numbers so wild females would mate with sterile males and fail to produce offspring.
Insecticides also played a role in pushing screwworm populations south into Central and South America.
McReynolds said there are no active cases in Kansas, and officials want producers to be confident in the safety of the food supply even as they remain vigilant for signs of the parasite.
“New World screwworm is a treatable disease,” she said. “In my role, we deal with a lot of diseases that aren’t treatable and are absolutely devastating. This one certainly is an issue, but it is treatable, and it is not a concern for food safety.”
Kansas’ response is built on what McReynolds called a “three-legged stool”: surveillance, treatment and movement control.
“Surveillance is keeping your eyes on animals, monitoring and reporting cases,” she said. “Treating those animals that have lesions is really important. And then movement control — we’re not trying to stop movement completely; we’re just trying to make smart movements, making sure animals show no signs of wounds or that any wounds have been properly treated.”
She encouraged producers not to delay reporting out of fear that their operations will be shut down.
“If we do get an infested zone, it’s not that we’re completely stopping movement,” McReynolds said. “You can move; we’re just going to have some extra steps in place, so you have to plan ahead. We’re taking those steps to protect everyone else outside that infested zone.”
Because wildlife can also harbor the parasite, Olds said, officials must consider animals that do not respect fences or quarantines.
“I’ve never met a whitetail deer that respected a fence,” she said.
Both experts emphasized the same two messages: watch animals closely and report suspicious wounds, and be assured that the parasite does not threaten the safety of meat or other animal products in the marketplace.
“Eyes on animals — that’s extremely important,” McReynolds said. “Continue to monitor all your livestock, as well as your dogs and cats. If you see anything that has you concerned, reach out so we can determine the extent and control the spread as much as possible, while maintaining confidence in our food supply.”
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