The U.S. Department of Agriculture recently confirmed the first occurrence of the New World screwworm in an American cow in roughly six decades. This marks the first detection of this agricultural pest in U.S. cattle since it was eradicated in 1966.
Screwworms are parasitic flies that deposit their eggs in open wounds, cuts, and body openings such as eyes, ears, mouth, and genitals of warm-blooded animals, including humans. Once hatched, the maggots burrow into the skin, resulting in painful and malodorous wounds.
During the first half of the 20th century, the southern U.S. and Mexico experienced severe screwworm outbreaks. However, a successful initiative known as the sterile insect technique, which involved releasing sterile flies in Panama, led to the collapse of the screwworm population in these regions.
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Despite its eradication in those areas, the New World screwworm persisted in the Caribbean and South America. In 2005, it was estimated to cause annual economic losses of about $6.1 billion in today’s terms. Recently, the fly has been migrating north through Central America, leading experts to warn that its arrival in the U.S. was imminent.
The recent case was identified in a three-week-old calf in Zavala County, Texas, with the infection located in the calf’s umbilical region, as reported by the USDA.
“Protecting our livestock industry is a national security issue of the utmost importance, and USDA is wasting no time in taking action,” stated Dudley Hoskins, the agency’s undersecretary for marketing and regulatory programs. “The United States has defeated this pest before, and we will do it again.”
In response, USDA and Texas authorities are implementing “immediate action” to manage the threat. These measures include forming an incident command team with the Texas Animal Health Commission, setting up a 20-kilometer quarantine zone around the infection site, deploying sterile New World screwworm flies both from the ground and air, capturing flies along the border, screening local wildlife, and conducting community outreach.
Residents near Zavala County should inspect their pets or livestock for signs of infection, such as draining or enlarging wounds with screwworm maggots and eggs around body openings, advises the USDA. Suspected infections should be reported to state animal health officials or local USDA veterinarians.
While New World screwworms infrequently infect humans, they can affect individuals living in or traveling to endemic regions. Those who spend significant time outdoors with open wounds are at greater risk. Anyone suspecting an infection should seek immediate medical attention. The U.S. Centers for Disease Control and Prevention advises against self-removal of maggots, as surgical removal by a healthcare provider may be necessary.
To minimize the risk of infection, the CDC recommends keeping wounds clean and covered, sleeping indoors with closed windows or screens, and using insect repellent or wearing long-sleeved clothing.
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