The arrival of New World screwworm in the U.S. is too close for comfort, said Chris Chinn, Missouri Department of Agriculture director.
“It is important for Missouri producers to be aware,” she said, “but not to panic.”
State agriculture officials have been preparing for this possibility, and they now warn farmers to monitor their herds closely and treat infections quickly to protect their animals.
“It’s a very aggressive pest and needs to be recognized early, so treatment can be instituted as soon as possible,” said Steve Strubberg, Missouri state veterinarian. “They are susceptible to most common pesticides.”
New World screwworm is a fly whose larvae feed on the living tissue of warm-blooded animals. It can infest any open wound, spread rapidly and be fatal without treatment.
How to spot an infestation
Finding an infection site can be problematic. In Mexico, reported infections started from a tick bite or a vampire bat bite.
“Thankfully we don’t have the vampire bat, but we do have ticks,” Strubberg said. “It can be as small as that.”
The most devastating time for a herd outbreak is during calving or lambing season when the navel is infested.
“If we get to the point where we’re having populations in Missouri during our fall calving season, we’re going to want people to get out there and treat those navels immediately,” Strubberg added. “That seems like most of the cases in southern Texas right now are calf navels.”
Strubberg outlined steps farmers can take, which include watching their animals more closely every day, even multiple times a day.
Here’s how to prepare:
- Implement strong fly and tick control protocols.
- Clean, treat and cover all open wounds immediately.
- Consider delaying castration, dehorning or branding to prevent open wounds.
- Register your farm for a premises ID, so the Missouri Department of Agriculture can notify you if NWS is confirmed in the state.
- Treat areas where procedures are performed.
Here are things to inspect for:
- bloody or light-colored drainage from cuts or wounds
- wounds that rapidly enlarge for no reason
- white or cream-colored runny substance (eggs) in and around wounds
- presence of maggots that burrow deeper and more aggressively than normal fly larvae
- behavioral changes including irritation, head shaking and reduced appetite
Take these actions:
- Report suspected cases immediately.
- Do not wait for confirmation. Treat right away.
- Trained personnel can collect samples and confirm detections quickly.
If NWS arrives on a farm, Strubberg said trained personnel and veterinarians can collect the larvae. Ultimately, identification is done at the National Vet Services Lab in Ames, Iowa.
Beyond on-farm management, producers must also consider the broader economic implications.
What does this mean for cattle markets?
According to University of Missouri Extension business specialist Wesley Tucker, the economic reality may be unavoidable as producers face increased costs for monitoring and treatment, potential marketing restrictions, and possible changes to production practices — even if they never see a case on their farm.
He explained that restricted animal movement could mean loss of marketing opportunities.
Currently, Missouri imposes the following transportation rules:
- Animals from states with infested zones (but not within the zone) need a Certificate of Veterinary Inspection (CVI) stating: “All animals were inspected and found free of evidence of NWS infestation and have not originated from or transited through an NWS-infested zone.”
- Animals from within infested zones must meet state of origin requirements, obtain entry permit from Missouri State Veterinarian’s Office, and have a CVI stating animals are free of NWS.
“Depending on how widespread the issue becomes,” Tucker added, “there will be quarantine zones and restrictions on animal movement. This can have major impacts on cattle movement throughout the country and traceability of animals as they move throughout the production system.”
Still, when it comes to markets, he said, there is an overriding question: What, if any, impact will this have on beef demand?
Is beef still safe to eat?
All three agree that New World screwworm is an animal health issue, not a food safety issue.
“It’s important that we continue to emphasize that the food supply is safe,” Strubberg said. “These animals are treated with products that are used on food-producing animals regularly, and after treatment, and an appropriate withdrawal period, those animals can continue to be within the food supply.”
But Tucker said the internet can influence perception.
“You never know how consumers will interpret the information and respond,” he said. “So, it is important for everyone to continue to educate their friends and neighbors that beef is still safe and nutritious.”
If demand holds steady, will there be enough supply to fill it?
“With cattle numbers at historic lows, NWS creates an additional headwind slowing expansion of the nation’s herd,” Tucker explained. “If NWS causes cattle losses in the South, it reduces the beef supply even further, potentially raising prices even more.”
Missouri’s response continues
Strubberg led a statewide working group over the past year, tracking the pest’s northward movement and creating the response plan.
The group includes officials from USDA, the Missouri Department of Conservation, the Missouri Department of Health and Human Services, and University of Missouri Extension.
“Now that NWS has been detected,” Chinn said, “the Missouri response plan is being followed.”
For more information or to report suspected cases, producers can contact the Missouri State Veterinarian’s Office at 573-751-3377, or visit agriculture.mo.gov or screwworm.gov.
Early detection and rapid response remain a beef producer’s best defense against this emerging threat.