Editor’s note: This story has been updated to reflect new information.
The New World screwworm has now been detected in three Texas counties, with New Mexico reporting its first case in a dog — more than 400 miles from the original outbreak zone in Texas.
Three additional cases of New World screwworm (NWS) were confirmed in the United States – a calf in La Salle County and a goat in Gillespie County, Texas and a dog in Lea County, New Mexico, by the United States Department of Agriculture on Monday, June 8.
The Lea County dog case is a USDA reclassification that was originally announced as occurring in Andrews County, Texas, according to a department update.
“While the veterinarian who reported the case is located in Texas, the dog resides at a household in Lea County, New Mexico. Therefore, the location of the case will be reclassified to be the first case detected in New Mexico,” read a USDA news release.
USDA said it believes the Lea County, New Mexico, case is isolated because of the dog’s recent travels, but the “exposure history remains unknown.”
These three new cases come on top of the two cases confirmed on Wednesday, June 3, and another on Friday, June 5 — in Zavala County in South Texas.
The NWS threat to the U.S. food supply remains low, as the USDA reports that any affected animal would “be identified during USDA Food Safety and Inspection Service inspection, and no contaminated product would enter commerce.”
USDA and the Texas Animal Health Commission (TAHC) continue to lead the response to the NWS, with a reported 75 people actively responding on the ground and hundreds more around the country providing laboratory diagnostics, logistics, treatment distribution, air operations, outreach, operational planning and resource support for the response.
Additionally, both USDA and TAHC have done the following to limit the spread of NWS:
According to the USDA, the department is continuing its sterile fly release operations over the infested areas and along the U.S.-Mexico border.
Starting on Tuesday, June 9, aerial dispersal flights originating from the sterile fly dispersal facility at Moore Air Base in Edinburg, Texas, will begin.
Due to the nature of the releases, USDA said it is possible that sterile NWS flies could be caught and reported, but it has taken steps to ensure officials can differentiate between sterile and wild NWS flies.
According to the USDA, the New World screwworm (NWS) is a parasitic fly that impacts livestock, pets, wildlife, and, less commonly, people and birds. The fly’s larvae feed on the living tissue of warm-blooded animals.
USDA reports that the current risk to animals and people in the United States remains very low and that NWS is not contagious.
Rather, screwworm infestations begin when a female fly lays eggs on a wound or body opening. The eggs hatch intolarvae that burrow into the wound and feed on living tissue, then after about 7 days of feeding, larvae drop to theground, burrow into the soil, and pupate.
The adult screwworm fly emerges from the soil after 7 to 54 days.
Adult NWS flies have orange eyes, a metallic blue or green body and three dark stripes across the back, according to the USDA.
The telltale signs of a screwworm infection are the growing wounds or lesions and the presence of feeding maggots on still-alive animals. Some other species of maggot can be found on live animals, said Dr. Jennifer Bloodgood, assistant professor of practice and wildlife veterinarian at Cornell University, but the difference is what they’re eating. NWS feeds on healthy, living flesh, while most other maggot species feed on dead tissue.
It can be difficult to discern the difference, especially with wild animals you cannot observe closely. Because of this, public health officials encourage the public to report any suspected cases.
Mateo Rosiles is the Texas Connect reporter for USA TODAY and its regional papers in Texas. Got a news tip for him? Email him at mrosiles@usatodayco.com.
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