Threat to American Livestock – The New World Screwworm (NWS) fly, once eradicated in the U.S. back in 1966, has resurfaced as a serious concern following an outbreak in Mexico.
This alarming news led to a halt in imports of cattle, horses, and bison along the southern border. USDA Secretary Brook Rollins made the announcement via a post on X, stating, “Due to the threat of screw bugs in the New World, I am announcing the immediate import of live cows, horses and bison through the border ports south of the United States.”
“It took our cattle industry 30 years to recover when this devastating pest invaded America. This cannot happen again,” she emphasized.
What are the New World Screwworms?
The USDA’s Animal and Plant Health Testing Service (APHIS) classifies NWS as an endemic species in Cuba, Haiti, the Dominican Republic, and various South American nations.
The NWS flies prefer wooded areas but typically search for hosts like cows and horses in grasslands. Females lay their eggs in the wounds or openings of warm-blooded animals. The hatching larvae (or maggots) then burrow into the flesh, which can lead to severe, often fatal damage.
These screw worms are named for the way their larvae bore into the meat, resembling the action of screws being driven into wood. APHIS notes that these pests can inflict major harm by tearing host tissue with a sharp mouth hook, creating wounds that attract even more flies to lay eggs.
While it’s rare, larvae can even infest humans, leading to painful infections and serious tissue damage.
Risk Factors and Prevention
Screwworms are primarily found in regions of South America and the Caribbean. According to the CDC, individuals traveling to those areas, spending time around livestock, sleeping outdoors, or having open wounds are at increased risk of NWS infestation. Vulnerable groups include the very young, elderly, and malnourished, as well as those who have recently had surgery.
Potential Impact
If another outbreak strikes U.S. soil, the USDA warns that it could result in severe consequences for pets, livestock, and even humans due to screw worm myopathy.
Historical data shows that livestock producers in the southwestern United States were losing between $50 million to $100 million annually before the NWS was eradicated in the 1950s and ’60s. The USDA notes that these losses were likely due to higher livestock populations and the expansive geographical areas where the NWS could thrive.
Even though the NWS was eradicated in 1966, there was a resurgence in the Florida Keys in 2016, affecting local deer populations. By March 2017, however, the outbreak was contained.
