By Burt Rutherford Contributing Editor
It’s very likely that it’s not a matter of if but when screwworm flies cross the southern border and make their way into the United States. And it’s likely that the first indication that an incursion has taken place won’t be in cattle, according to Callie Willilngham, DVM, president-elect of the American Association of Bovine Practitioners (AABP) and private veterinary practitioner in Texas and Canada.
“There’s a good chance that we’re not going to identify it first in cattle,” Willingham said, speaking to media during the recent AABP conference in Omaha, Neb. “There’s a good chance it’ll be in a dog or cat or another human case,” she said.
Or wildlife, which crosses back and forth across the border between the United States and Mexico. To that end, the USDA tick riders that patrol the border looking for fever ticks are now also on the lookout for animals that may have a screwworm larvae infestation. In addition, fly traps have been established along the border to screen for any screwworm flies that may have winged their way north.
SHOULD A SCREWWORM INCURSION HAPPEN, USDA WILL BE THE LEAD AGENCY IN MOUNTING A RESPONSE.
“We’ve met with stakeholders across the veterinary profession and the cattle industry” on the screwworm issue, according to Dave Sjeklocha, DVM, AABP president and a technical service veterinarian for Merck Animal Health. “AABP is working hard to ensure that veterinarians are vigilant, are aware of what it looks like. Our primary role is to make sure a diagnosis is reported immediately.”
The female screwworm fly lays her eggs in an open wound. It can be as small as a cut from a fence or mesquite thorn or even the opening in a calf’s navel right after the umbilical cord falls off. The eggs develop into larvae, which feed on living flesh.
Given that any warm-blooded animal can be infected by screwworm larvae, including humans, Sjeklocha said it’s important for human medical doctors to be aware of the threat and know to report a diagnosis right away.
“It is a very One Health response [we] need,” Willingham added, “because it impacts everyone and we don’t know where that incursion is going to be.”
Screwworm flies have been eradicated in the United States for many years, thanks to an extensive effort to produce sterilized male flies, which would mate with female flies. The females would lay eggs, but they were sterile and wouldn’t hatch into larvae.
That’s still the most effective approach to combating a screwworm fly incursion, Sjeklocha said, but the facilities that once produced sterile male flies have been mothballed for decades. So, while ramping up sterile-fly production is essential, it will take time. According to Fred Gingrich, DVM, AABP executive director, “AABP is very appreciative of Ag Secretry Rollins and USDA in ensuring that they’re putting the funding behind [re-establishing sterile fly facilities], which is what we need.”
Should a screwworm incursion happen, USDA will be the lead agency in mounting a response, according to Willingham. To prepare for a possible incursion, USDA is working with FDA to create emergency-use authorizations for medicines and treatments that are not approved in the United States but are labeled for use in other countries, “so that we would have access to those medications and treatments if it does arrive.”
However, medications and treatments are just part of the effort to have an arsenal in place, according to Gingrich. “We’re going to consider everything possible to combat this threat. That might include novel therapies and vaccines,” he said.
“If you’re a rancher in Texas or a veterinarian in Texas caring for those cattle, it’s a big challenge when you’re talking about having to individually treat those animals on thousands of acres of open rangeland,” Gingrich said. “How are we going to accomplish that? We’re fortunate that these conversations are occurring now at all levels because we’ll be more prepared.”
