The U.S. Department of Agriculture announced three new cases of New World screwworm on Monday, including the first cases in dogs and goats, bringing the total case count in the country to five. He also pledged to intensify and accelerate mitigation efforts for screwworm, a parasitic fly that the nation declared eradicated in the 1960s.
At a news conference Monday, federal and state officials in Texas said they were using AI-powered technology to monitor screwworm populations, training ranchers to recognize infections in their livestock and expanding the number of facilities that produce and disperse sterile flies, which are the primary tool for screwworm control.
Authorities are also considering granting emergency authorization to a new strain of genetically modified flies that could make the production of sterile flies faster and more efficient.
“We prevented and eradicated this pest before,” Gov. Greg Abbott, R-Texas, said during the briefing. “We can do it again.”
The three new cases were identified in a calf in La Salle County, Texas; a goat in Gillespie County, Texas; and a dog in Lea County, New Mexico. It is unclear whether the dog acquired the parasite in the United States; Although officials initially indicated the dog may have recently been in Mexico, they later said its travel history was unknown.
The agency reported the first two cases last week, both in calves in Zavala County, Texas.
Still, Agriculture Secretary Brooke Rollins noted during the news conference that the resurgence of the New World screwworm was not unexpected.
Over the past few years, the insect has traveled north through Central America. Ms. Rollins credits monitoring and containment efforts for slowing the spread of the pest to Texas.
“All the models showed that the New World screwworm would be here in Texas early last summer, so we bought ourselves an extra year to prepare for this moment,” Ms. Rollins said.
The New World screwworm is a blowfly that feeds on living flesh. Adult females lay their eggs in open wounds or orifices of warm-blooded animals. When the eggs hatch, the larvae enter the wound and consume the animal's tissue. Screwworm infections left untreated can kill animals within a week.
In humans, screwworm infections are rare. Last year, U.S. health officials confirmed a travel-related case in a Maryland resident who had recently traveled to El Salvador, but no human cases acquired in the country have yet been reported.
The parasitic fly was a serious scourge of livestock in the southern United States in the early 20th century. Authorities eradicated it using the sterile insect technique, which involved raising huge numbers of flies, sterilizing them by exposing them to radiation, and then releasing them into the wild. The screwworm population plummeted as wild females, which mate only once in a lifetime, bred with sterile males.
The technique is based on the release of sterile males, but it has not been practical to separate males and females produced in mass breeding facilities. Consequently, both male and female flies are usually raised, sterilized, and released.
An all-male variety would make the approach much more efficient. Recently, scientists have moved toward creating an all-male strain with NovoFly, a genetically modified version of the New World screwworm.
“It will allow us to almost instantly double the number of sterile flies we put into the fight,” Scott Hutchins, USDA undersecretary for research, said of NovoFly at Monday's press conference.
NovoFly contains genes for two unusual proteins. In men, these proteins have few known effects other than sterility. But they cause the females to die in the embryonic stage, so the only NovoFly that reaches adulthood (unless tetracycline, an antidote to genetic modification, is administered) is a sterile male.
“It's never been tested in the field and that has to be the next step,” said Maxwell Scott, an entomologist at North Carolina State University, whose lab helped develop NovoFly.
NovoFly is considered a pesticide; It would typically be subject to a lengthy approval process before being released into the environment. However, because of the public health and economic dangers associated with a screwworm outbreak, the Environmental Protection Agency is considering an emergency waiver that could expedite its release.
That could make NovoFly one of the few genetically modified animals ever released into the wild. In 2006, a modified version of the highly invasive pink worm was released in Arizona. More recently, the Oxitec mosquito, created to slow the spread of malaria, Zika, yellow fever and other diseases, has been released in mosquito-infested areas of the world, including the Florida Keys.
It is not yet clear whether NovoFly's emergency waiver will be approved, but the USDA has made clear that it will continue to support the effort, as well as others that could bring the United States closer to complete screwworm eradication.
“We're going to turn over every rock to find more sterile flies,” John Bellinger, USDA's senior adviser for New World screwworm preparedness, said during Monday's briefing. “We have to be ready next spring.”
