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A flesh-eating parasite has been detected in a dog in Arizona, marking the state's first confirmed case of New World screwworm as infestations continue to be reported across the U.S.-Mexico border region.
The U.S. Department of Agriculture (USDA) confirmed the case in Cochise County, Arizona, on Wednesday, after laboratory testing identified New World screwworm in samples taken from the animal.
A local veterinarian examined the dog on the evening of October 26 and found a wound on its back heavily infested with maggots, according to the Arizona Department of Agriculture.
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New World screwworm is a parasitic fly whose larvae feed on the living tissue of warm-blooded animals, and infestations can cause severe wounds and significant harm if they are not identified and treated promptly.
The latest case is Arizona's first detection of the parasite, as New World screwworm was last eradicated from the United States in 1966, as per the Texas Animal Health Commission.
The affected dog is receiving veterinary care, while state and federal authorities coordinate a response to contain the infestation.
The Arizona detection brings the number of states reporting confirmed animal cases in the current outbreak to three, following earlier detections in Texas and New Mexico.
The USDA reported 71 confirmed animal cases nationwide since June as of October 28, with 18 remaining active, and detections spanning Texas, New Mexico and Arizona.
June 3: First Confirmed U.S. Animal Case
The USDA confirmed the first animal case of New World screwworm in the United States during the current outbreak on June 3 this year, marking the parasite's return after its previous eradication.
The infestation was found in a calf in Zavala County, Texas, according to the Texas Animal Health Commission.
The calf has since recovered, and the individual case is now classified as inactive, but the detection came as the parasite spread into Texas and New Mexico, raising concerns about the potential impact on the U.S. cattle industry.
The Trump administration has faced criticism from some ranchers, animal health experts and industry observers over separate decisions to reopen portions of the U.S.-Mexico cattle trade while outbreaks remain active on both sides of the border.
Federal officials have also authorized additional measures to help protect livestock. The U.S. Food and Drug Administration (FDA) issued an Emergency Use Authorization for Bimectin, a generic ivermectin injection, to help prevent New World screwworm infestations in cattle.
The authorization allows the drug to be administered within 24 hours of birth, during castration procedures, or when animals develop wounds that could attract screwworm flies.
It was the FDA's 14th emergency authorization related to the parasite since officials intensified their response to the outbreak.
“This authorization reflects the FDA’s commitment to expanding generic drug options against New World screwworm,” Timothy Schell, director of the FDA's Center for Veterinary Medicine, said in a press release.
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“By authorizing both generic and pioneer products, the Agency is ensuring producers aren’t dependent on a single manufacturer or product to protect their herds.”
Summer: Cases Reported in Texas and New Mexico
Following the initial Texas detection, further animal infestations were confirmed in Texas and New Mexico.
Texas has reported cases across livestock premises and counties, according to the Texas Animal Health Commission, and authorities have been monitoring affected areas and implementing measures to limit the parasite's spread.
Official orders published by the Texas Animal Health Commission documented detections in a goat in Terrell County on June 22, a bovine in Brewster County on July 9, a sheep in Pecos County on July 14 and cattle in Starr County on July 18.
New Mexico has also reported infestations, prompting officials to monitor the situation near the Arizona border.
The spread across the two states raised concerns about the potential for the parasite to reach additional areas, particularly southern Arizona.
The Arizona Department of Agriculture said before its state's first confirmed case that it had been communicating with livestock owners, pet owners, tribal partners and animal-health professionals about detections in Texas, New Mexico and Sonora, Mexico.
October 15: Additional Cases in New Mexico
On October 15, federal and New Mexico officials announced two additional cases in Grant County, involving an equine and a bovine, according to an Arizona Department of Agriculture update from October 20.
The findings expanded an existing infested zone westward and established a second infested zone in southwestern New Mexico, around 10 miles from Arizona's border.
At the time, Arizona officials urged pet and livestock owners to monitor their animals for unusual wounds containing maggots and to report suspected infestations promptly.
The department said southern Arizona could potentially be affected year-round, while sustained cooler temperatures were expected to limit screwworm activity in northern Arizona.
October 21: First Confirmed Case in U.S. Wildlife
New World screwworm was detected in an elk in Texas on October 21, marking the first confirmed case of the flesh-eating parasite in U.S. wildlife during the current outbreak.
The U.S. Department of Agriculture (USDA) confirmed the detection in a female elk in Pecos County, Texas. The animal was on a game ranch and was reported to authorities after being harvested by a hunter.
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A sample collected from the elk was identified as New World screwworm at the USDA Agricultural Research Service's Knipling-Bushland U.S. Livestock Insects Research Laboratory in Kerrville, Texas.
The discovery followed months of detections in domestic animals, and detections were reported in several Texas counties, including La Salle, Gillespie, Edwards, Tom Green and Sutton.
The elk detection prompted the Texas Animal Health Commission to modify an existing infested zone, while the USDA and the Texas Parks and Wildlife Department began additional wildlife surveillance in the area.
Officials urged hunters and landowners to inspect animals for suspicious wounds, maggots and other signs of infestation, and to report suspected cases promptly.
October 28: Arizona Confirms Case in a Dog
Arizona's first confirmed case was identified in the dog in Cochise County, near the Mexican border.
State Veterinarian Dr. Ryan Wolker said: "We have been preparing for this possibility for a long while and are acting swiftly."
"Because of the extensive outreach, coordination, and surveillance already in place, Arizona producers, veterinarians, and pet owners know what to look for and how to report suspected cases. That preparation is allowing us to move quickly to protect animal health in the state."
The USDA and Arizona animal-health officials are implementing a response that includes establishing a 20-kilometer infested zone around the detection, introducing animal movement controls, increasing surveillance and trapping, and releasing sterile flies.
Officials are also conducting targeted outreach to local producers, veterinarians and communities.
What Should Pet Owners Look Out For?
New World screwworm can affect domestic animals, including dogs and cats, as well as livestock and wildlife.
The parasitic fly lays eggs on or near wounds, and its larvae feed on living tissue. Infestations can cause severe wounds and animal suffering if they are not detected and treated quickly.
The USDA is urging animal owners in affected areas to inspect their animals daily for signs of a possible infestation.
Warning signs include:
- Draining or enlarging wounds - Check for wounds that are draining or becoming larger.
- Maggots or egg masses - Look for maggots or clusters of eggs in wounds.
- Signs of discomfort or irritability - Monitor animals for unusual discomfort or irritability.
- Lesions around body openings - Check for lesions around the ears, nose, genital area and umbilicus.
The USDA advises anyone who suspects an infestation to contact a veterinarian, state animal-health official or the USDA immediately.
Pet owners should not delay seeking veterinary attention if they find maggots in a wound or notice a suspicious lesion.
Although New World screwworm can also affect people, the CDC says the current risk to the public in the United States is very low.
In its October 22 update, the CDC said there had been no reports of human infestations acquired in the United States during the current outbreak.
The agency reported that Central American countries and Mexico had recorded more than 209,400 animal cases and more than 2,800 cases in people.
People who notice a suspected infestation should seek medical attention. The CDC advises the public to consult its New World Screwworm outbreak guidance for the latest information.
Contact Newsweek editors on this story: John Fitzpatrick and Gray R. Thomas
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