The first case of the New World screwworm in a U.S. cow in about 60 years has been detected, the U.S. Department of Agriculture confirmed yesterday. It is the first instance of the agricultural pest in cattle since it was eliminated in the U.S. in 1966.
Screwworms are parasitic flies that lays their eggs in open wounds or cuts or in the eyes, ears, mouth, nose or genitals of warm-blooded animals—including humans. The maggots hatch and burrow through the skin, causing painful, foul-smelling wounds.
Livestock in the southern U.S. and Mexico suffered devastating screwworm outbreaks in the first half of the 20th century. But the parasite was eliminated in those nations thanks to a wildly successful effort called the sterile insect technique, which involved the release of sterile flies in Panama that caused the fly population to collapse.
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Yet the New World screwworm remained endemic to the Caribbean and South America, where, in 2005, it was estimated to cause annual economic losses of around $6.1 billion in today’s dollars. And in recent years the fly has been spreading northward through Central America. Experts had been warning that it was only a matter of time before it arrived in the U.S.
The new infection was detected in a three-week-old calf in Zavala County, Texas; it was found in the calf’s umbilical area, according to the USDA.
“Protecting our livestock industry is a national security issue of the utmost importance, and USDA is wasting no time in taking action,” said Dudley Hoskins, the agency’s undersecretary for marketing and regulatory programs, in a statement. “The United States has defeated this pest before, and we will do it again.”
USDA and Texas officials are taking “immediate action” to contain the threat, according to the statement. Efforts include forming an incident command team with the Texas Animal Health Commission, establishing a 20-kilometer perimeter around the site of the infection with quarantines and movement controls, releasing sterile New World screwworm flies from the ground and the air, trapping flies along the border, screening wildlife in the area and doing outreach in local communities.
People who live around Zavala County should check their pets or livestock for signs of an infection—for example, draining or growing wounds and screwworm maggots and eggs in or around body openings, the USDA says. If they suspect an infection, people should contact their state animal health official or local USDA veterinarian.
New World screwworms rarely infect humans, but they can infect people who live in or travel to areas where the flies are endemic. People who spend a lot of time outside and have open wounds are most at risk. Anyone who suspects they may have an infection should seek immediate medical care. People should not try to remove maggots themselves—a health care provider may need to remove them surgically, according to the U.S. Centers for Disease Control and Prevention.
To prevent infection, the CDC advises keeping wounds clean and covered, sleeping indoors with closed windows or screens and using insect repellant or wearing long-sleeved clothing.