Cases of a flesh-eating infection miles from Texas’ border with Mexico are alarming officials about the return of a parasitic fly that was once eradicated.
Earlier this week, the U.S. Department of Agriculture reported active cases of New World screwworm in the Mexican state of Nuevo León. In an April 20 statement, Texas Agriculture Commissioner Sid Miller said one infected calf, about 62 miles from the border, was the northernmost active case from the parasitic New World screwworm fly to date, calling it a “flashing red warning sign.”
Latest available USDA data, as of April 21, showed more recent active cases among cattle in Tamaulipas, a Mexican state bordering Texas. USDA has said there’s no current risk to livestock, pets or people in the United States. American officials have closed southern ports of entry to livestock trade.
New World screwworm flies feed on warm-blooded animals and humans to create painful, foul-smelling wounds, according to the U.S. Centers for Disease Control and Prevention. They spread when female flies lay eggs in an open wound − sometimes as small as a tick bite − or in an animal’s nose, eyes, ears or mouth. Then, eggs hatch maggots that burrow and eat live tissue. After a few days, larvae drop and burrow into soil, later emerging as mature flies.
USDA declared the United States free of indigenous screwworms beginning in 1966, using a technique of sterilizing male flies. North America eradicated New World screwworm by the 2000s.
In the following decades, New World screwworm has steadily returned northward from endemic regions in South America. Parasitic flies have caused outbreaks in Central America and Mexico, which is a primary supplier of cattle to the United States.
A Nature study published in July said climate change contributes to its re-emergence due to hotter temperatures and changing weather. This creates more favorable conditions for flies to spread in Texas, home to the nation’s largest cattle industry, as well as other parts of the southern United States. Economic losses by the return of New World screwworm could run into billions of dollars, the study found.
There have been isolated cases of people infected with New World screwworm who have returned to the United States from international travel. A small outbreak last occurred in 2017 in the Florida Keys.
Eduardo Cuevas is based in New York City. Reach him by email at emcuevas1@usatoday.com or on Signal at emcuevas.01.