The United States is halting imports of livestock from Mexico to protect U.S. livestock from a flesh-eating parasite called the New World Screwworm.
The New World Screwworm, or the NWS for short, is a parasitic fly that was eradicated in the U.S. in the 1960s. The fly gets its name for how its maggots feed on an animal by burrowing, or screwing, into an open wound, creating “extension damage by tearing at the hosts’ tissue with sharp mouth hooks,” the Animal and Plant Health Inspection Service states.
The import suspension was announced by U.S. Department of Agriculture Secretary Brooke Rollins on Sunday, May 11, following a detection of the flies in remote farms about 700 miles south of the Mexico-U.S. border. The suspension will be reevaluated on a “month-by-month basis,” a USDA statement reads.
Here’s what to know about the New World Screwworm, including its past presence in the U.S.
New World Screwworm: Parasite threat forces US to halt cattle imports from Mexico
What is the New World Screwworm?
The New World Screwworm is a parasitic fly, about the size of a common housefly. They have orange eyes, a metallic blue or green body and three dark stripes along their backs, according to the Animal and Plant Health Inspection Service.
The fly gets its name for the behavior of its maggots, which burrow, or screw, into an animal’s open wound, feeding as they go. The New World Screwworm has sharp mouth hooks, allowing them to burrow deep into an animal’s flesh.
New World Screwworms can infest livestock, pets, wildlife, birds and in rare cases, people.
How does a New World Screwworm infestation start?
New World Screwworms spend most of their time in forests and wooded areas but can seek animals in pastures and fields, if available. According to the USDA, flies are attracted to open wounds, even as small as a tick bite.
A screwworm infestation begins when a female lays eggs near an open wound of a warm-blooded animal. Within a few hours, the eggs hatch into larvae (maggots) and burrow into the wound, eating the living flesh. After about seven days of feeding, the larvae drop to the ground, burrow into the soil and pupate, becoming an adult screwworm, according to the USDA. Flies emerge from the soil seven to 54 days later and then the cycle begins again.
During a lifespan, female New World Screwworms can lay up to 3,000 eggs, the USDA states.
Infected animals tend to show the following signs:
Irritated behavior
Head shaking
Smell of decay
Evidence of a fly strike
Presence of fly maggots in wounds
Is the New World Screwworm a danger to humans?
New World Screwworms can infest people, but this is rare, according to the Centers for Disease Control and Prevention. People are more susceptible if they travel to areas where the flies are prevalent, including South America and the Caribbean.
Though rare, symptoms of a screwworm infestation in humans includes:
Unexplained skin wounds or sores that don’t heal
Skin wounds or sores that worsen over time
Painful skin wounds or sores
Bleeding from open sores
Feeling larvae movement within a skin wound or sore, nose, mouth or eyes
Seeing maggots around or in open sores
A foul-smelling odor from the site of an infestation
Secondary bacterial infections can occur and may cause fever or chills.
When was the New World Screwworm eradicated from the US?
The New World Screwworm first became a significant problem in the U.S. in 1933, after shipment of infested animals from the Southwest, according to the USDA.
By the 1950s, the federal government established the Sterile Insect Technique, a method that utilized radiation to sterilize male flies. These mass-produced sterile males were released into target areas and mated with females, which resulted in unfertilized eggs, according to the USDA. By the early 1960s, Southeast producers had lost between $50-100 million because of the infestations.
Fortunately, the Sterile Insect Technique was a success and New World Screwworms were officially eradicated by 1966, according to USDA. Ultimately, it cost the federal government $32 million to complete.
Greta Cross is a national trending reporter at USA TODAY. Story idea? Email her at gcross@usatoday.com.
This article originally appeared on USA TODAY: New World Screwworm: What is the flesh-eating parasite?
