USDA officials confirmed a second U.S. case of New World screwworm late Friday. The latest case was detected in a one-month-old calf in Zavala County, Texas. That’s approximately 5.6 miles from where the first U.S. case was confirmed just two days earlier.
On Friday, Canada banned the import of all cattle, horses and other livestock that had been in Texas at any time over the previous 21 days. Also on Friday, Texas Governor Greg Abbott issued a disaster declaration for his state. The declaration authorizes the use of all available state government resources to respond to the presence of screwworm.
In response to the latest case, USDA’s Animal and Plant Health Inspection Service has established a second 20-km infested zone around the detection site. Animal movement within those zones will be subject to quarantines, movement control and heightened surveillance.
On June 4, USDA began dispersing two million sterile screwworm flies twice per week by air. Sterile flies have long been one of the most effective tools to combat the invasive pests. Additionally, USDA is shipping an additional four million sterile flies per week to Texas. APHIS officials say these will be deployed via 24 strategically placed ground release chambers.
What should cattle producers do?
Adam Murray, who just took a job at West Texas A&M University and was the beef Extension specialist for Cornell Cooperative Extension, said producers should be vigilant of any animals with open wounds. That includes wounds as small as a tick bite or a small scratch. Murray noted that a significant number of issues may also arise during the calving process.
“Placenta coming out, an exposed umbilical cord, all of this blood will attract these insects. So there's a lot of fluid and aromas that are really going to attract them,” he said. “Castration is another time we see a lot of blood exposure that can attract these insects.”
Dan Buskirk, Extension beef specialist with Michigan State University, said young calves are especially vulnerable to infestation. On young calves, screwworm will most likely attack small wounds and navels.
“Those minor sorts of cuts and abrasions that you might have ignored, keep an eye on that now,” Buskirk advised. “Young calves will be susceptible when first born, too. When their navel is still wet, that's kind of fair game for those flies as well."
What makes New World screwworm different?
Like nearly all fly species, New World screwworms lay eggs that hatch into larvae, commonly known as maggots. But while most maggots eat dead tissue, New World screwworm larvae feast on live flesh.
According to Sally DeNotta, a University of Florida College of Veterinary Medicine professor specializing in equine internal medicine, screwworm maggots don’t look much different than a typical house fly maggot infestation. What is different is the host animal’s response.
“Because they (screwworm maggots) are feeding on live tissue, they’re actually quite painful to the host as opposed to dead tissue, which inherently has no feeling or sensation anymore,” DeNotta said. “Animals that are infected with New World screwworm tend to be quite bothered by the wounds and by the maggots, so one thing people can keep an eye out for is if the animal is particularly uncomfortable.”
If left untreated, screwworm-infested animals can die in a matter of weeks or be left with permanent disabilities. All warm-blooded mammals are susceptible to screwworm. However, if caught promptly, most animals can make a full recovery.
Concern up North?
Both Buskirk and Garth Ruff, Extension beef specialist with Ohio State University, said it is highly unlikely the flies will reach areas far north since they prefer warmer climates. Still, if the outbreak grows and cattle are allowed to cross state lines, the threat of a fly hitching a ride to the Upper Midwest or Northeast will grow.
“At any given time there’s like 500 trucks of just cattle on the road,” Buskirk said. “So, it will be artificially easy for us to move it around.”
"We're really in a kind of a wait-and-see pattern," Ruff said. “There's no reason for anybody to panic at this point. It's not in Ohio. It looks like USDA is trying to get a hold of this and keep it from spreading further north.”
Impact on consumers
If the outbreak grows, Murray said the biggest impact could ultimately be people questioning the safety of the nation’s beef supply.
Even though these New World screwworms can exacerbate wounds, kill cattle and cause other issues it does not affect the safety of the meat. Murray concedes that screwworm’s arrival in the U.S. will likely be a big news cycle. As consumers hear more about it, their concerns may also increase. Still, he hopes consumers will understand that screwworm is not a food safety issue.
“We have inspections in place that will remove the unwholesome, unsafe areas if they are affected by screwworm, but the rest of the carcass should be fine,” Murray said. “So, it's going to be really important for our cattle producers, our beef producers, the beef and cattle industry as a whole … to educate consumers that, yes, our beef is still okay.”