As a pork producer, you can’t personally control how far north the New World screwworm advances, but you can protect your own operations and interests as much as possible.
There are animal diseases for which pig producers have long been on alert and prepared to fight should they come across U.S. borders. One they might not have thought about in decades, or ever — depending on their age — is New World screwworm (NWS), or Cochliomyia hominivorax.
Unfortunately, it’s time to start learning about it again. Last November, Mexico reported NWS had been found inside its southern border, and in May the USDA’s Animal and Plant Health Inspection Service (APHIS) suspended imports of live cattle, horses and bison from Mexico. Recent reports have placed NWS as close as 370 miles to the U.S. border, and at this point it seems less “if” and more “when” NWS is in our country again.
So, what is this screwworm?
Gone for Decades
Native to the Western Hemisphere, the adult NWS is a parasitic fly that lays its eggs in the wounds or orifices of warm-blooded animals — cattle, pigs, pets, even humans (though rarely). It gets its name from the larval maggot, which feeds on the host by screwing itself into flesh. NWS used to be a common worry for livestock producers here, until the USDA and Southern states funded scientific research to mostly drive it outside U.S. borders about 60 years ago.
Between 1962 and 1975 alone, the U.S. and Mexico partnered to release more than 94 billion NWS flies rendered infertile through Sterile Insect Technique lab radiation. The treated males mated with non-treated females in the wild, resulting in population reduction, and by 1986 NWS was effectively driven south of Mexico as well.
In 1994 APHIS and Panama began collaborating to maintain a biological barrier near the Colombian border, which is a narrow land “pinchpoint” relatively easy and affordable to “blanket” with sterile males each year — and the flies have a difficult time crossing that much ocean from elsewhere in South America. During Covid, funding for improving/maintaining the Panama flies factory paused, and fertile NWS flies were back in Central America again by 2023.
In the 1970s, despite a Mexico-U.S. barrier zone, livestock producers in Southwest states still struggled with some infestations and economic losses. In 1976 Texas reported 1.5 million cattle and 333,000 sheep and goats infested with NWS. Adjusted for inflation, APHIS says this infestation now would cost the producers $732 million and result in a loss of $1.8 billion to the state’s economy.
Trade Disruptions
Beyond those APHIS numbers, I don’t have a detailed assessment of the potential market impact of NWS landing in our swine barns. If NWS is identified in the U.S., it’s likely there would be immediate trade restrictions imposed by at least some of our export partners until we demonstrate the country, or at least areas of it, are NWS-free. Although we don’t export many live pigs, and meat and other post-slaughter products are free of NWS, officials in other countries will likely not want to take any chances — particularly Japan, China, and Korea, which don’t have NWS.
How we’ve responded to the NWS in Mexico can tell us a lot about how other countries would likely react to us if and when we find ourselves in Mexico’s position. On top of that, there’s the reality that more than a few countries probably wouldn’t hesitate to take the chance to retaliate against this year’s broad U.S. tariffs.
I can note that southern producers should probably be more immediately worried and on the lookout for NWS because they are closer to Mexico and because the NWS thrives better in their climates than further north. However, this doesn’t mean Minnesota producers, for instance, are immune or shouldn’t also take steps to be certain their biosecurity measures are sound.
Another reason to worry more about possible NWS impact in the South is that the highest concentration of feral swine is in the Southeast (and California), creeping into the lower Midwest. Although most commercial pigs are indoors, in the South there are some raised in a transition barn environment, plus small-scale and show pigs that live outdoors, which could be exposed to nearby wild swine and other potential NWS carriers.
Be Proactive in Programs
I advise any pork producer not already participating in the Swine Health Improvement Plan (SHIP) or Secure Pork Supply Plan (SPSP) to enroll. These are federal-state-industry programs designed to increase confidence among U.S. trading partners in the safety and biosecurity of our swine production.
They provide producers information and assistance with preparing for potential disease, and maintaining business continuity if they do experience an outbreak. As a producer, you can’t personally control how far north the NWS advances, but you can protect your own operations and interests as much as possible.
Other biosecurity measures I recommend at this time are monitoring and education. Know which pigs have open wounds and monitor if they are not healing. Do the same for sows that have recently given birth, young pigs with recently notched ears or docked tails, and vulnerable young piglets generally most susceptible to illness. Also watch for:
● NWS flies are similar in size to house flies, with orange eyes, metallic blue-green body and 3 dark stripes on their back
● Be aware of these in wounds or other orifices: visible egg masses or maggots, bloody or purulent discharge, odor of decay or wounds that enlarge or deepen
● Behavioral signs of possible infection: head shaking, rubbing against surfaces to scratch or signs of pain like depression, irritability, inappetence or isolating
If you do suspect NWS, contact your vet immediately. If they believe it’s NWS, they will notify your state’s top animal health official and the APHIS veterinarian in charge, as well as collect samples for the National Veterinary Services Laboratories. The animal(s) will need to be quarantined until free of NWS and affected premises cleaned with approved larvacidal insecticide, then monitored weekly for a month after quarantine.
USDA Spending to Prepare
CBS News recently reported the USDA expects a new sterile flies factory to be up and running in southern Mexico this time next year. It is also planning to open a distribution center in southern Texas by the end of 2025 to import and distribute flies from Panama if necessary. The USDA wants the Mexican factory in place, according to CBS, because Panama can only breed up to 117 million flies a week and USDA wants capacity for at least 400 million.
Based on various news reports and veterinary warnings, it’s safe to presume NWS will show up either much closer to our border or in the country at some point. Without fearmongering, I do want producers to be as prepared as possible just in case.
Early adopters have been amassing and recording data for a quarter-century or so. How do we turn that data into information, and information into knowledge?
Finding the right balance between taking beneficial preventative measures and not spending an over-budgeted amount on pharmaceuticals
As a pork producer, you can’t personally control how far north the New World screwworm advances, but you can protect your own operations and interests as much as possible.
Finding the right balance between taking beneficial preventative measures and not spending an over-budgeted amount on pharmaceuticals
Finding the right balance between taking beneficial preventative measures and not spending an over-budgeted amount on pharmaceuticals
Finding the right balance between taking beneficial preventative measures and not spending an over-budgeted amount on pharmaceuticals
Finding the right balance between taking beneficial preventative measures and not spending an over-budgeted amount on pharmaceuticals
Finding the right balance between taking beneficial preventative measures and not spending an over-budgeted amount on pharmaceuticals
Dustin Coleman raises wean pigs under contract on his farm in Missouri.
Producers are extremely good at several things: working hard, caring for their animals, and planning.
