Should suburban pet owners fear screwworm’s return? Here’s what experts say

Pet owners in Illinois and elsewhere are advised to be mindful after the detection last month in Texas of a parasitic fly whose larvae feed off living tissue of warm-blooded animals.

While there currently are no widespread concerns regarding pet safety here, monitoring and public education efforts by animal and health officials involving the New World screwworm (NWS) have stepped up, according to the Illinois State Veterinary Medical Association.

Pet owners should be informed and watchful but not alarmed, emphasized Kate Brucker, president of the 1,800-member ISVMA.

“We don't want people to panic. By keeping an eye on things you'll be able to catch it faster if it does make it up to Illinois,” Brucker said.

“As a state association, we decided we needed to make sure the public was aware,” she added.

NWS can infest livestock, pets, wildlife, occasionally birds and in rare cases people, according to the Animal and Plant Health Inspection Service of the U.S. Department of Agriculture.

Attention has grown since the first animal case in the U.S. was reported June 3 in Zavala County, Texas. But the current risk to the public is very low, according to the Centers for Disease Control and Prevention.

As of Sunday, 35 confirmed animal cases had been reported, mostly in domestic sheep and cattle. All except one in New Mexico are in Texas, USDA notes at screwworm.gov.

“It's nothing we need to worry about yet,” says veterinarian Jason Szumski, medical director at Bartlett Animal Hospital. “We're answering questions as (pet owners) ask.”

Lori Ross, an emergency vet and medical director for Michigan-based Emergency Veterinary Care Centers, said NWS has not been detected in Michigan, Indiana or Illinois.

Still, “vigilance is critical,” she added.

“Since we are so aware, there's heightened surveillance to track it and stop the spread,” Brucker said.

Infestations typically begin when flies lay eggs in an open wound, surgical incision, skin injury or another opening in the body, ISVMA reports. NWS should be suspected if any wound is rapidly worsening instead of healing, veterinarians say.

Unlike common maggots, which typically consume dead tissue, screwworm larvae can infest healthy tissue.

See your vet if you notice maggots in a wound; wounds that get larger or deeper over a short time; foul odor or discharge; excessive licking, rubbing, scratching or head shaking; increased number of flies around an animal; or signs of pain, discomfort, lethargy or decreased appetite.

“The good news for small animals is most of the medication for fleas and ticks is the treatment,” Szumski said.

Ross noted the U.S. Food and Drug Administration issued its first Emergency Use Authorization for certain drugs to treat screwworm infestations in dogs and cats.

Each Midwestern state has its own requirements for livestock movement and in some cases companion animals, she added. Many states also have implemented additional import requirements and documentation and treatment protocols for susceptible animals, she added.

“Travel history is important to mention to the vet,” Brucker said.

NWS is named for the maggots' behavior as they burrow into a wound and feed. They tear at tissue with sharp mouth hooks the wound can become larger and deepen as more maggots hatch, causing serious, often deadly damage, according to USDA.

It was eradicated from the U.S. in 1966 and a small outbreak in the Florida Keys in 2017 was eliminated, according to USDA.

But NWS reemerged in Central America and Mexico, according to CDC, with one human case confirmed in August 2025.

Multi federal, state and local agencies are working to prevent the spread among people and animals, the CDC reported.