Work continues to keep New World screwworm out of country

WASHINGTON — The New World screwworm is a devastating pest that is endemic to Central and South America.

“We have not had a positive on our side of the border,” said Sigrid Johannes, senior executive director of government affairs for the National Cattlemen’s Beef Association, on April 15.

“As of today, Mexico has registered more than 20,000 cases since it first hopped the border from Guatemala to Southern Mexico and they consider about 1,240 of those to be active cases,” said Johannes during a webinar hosted by the NCBA.

“The vast majority have shown up in bovines, but they have also had cases in equines and some minor cases in dogs, cats, wildlife, humans and birds,” she said.

The New World screwworm is a fly.

“The larvae is the screwworm part,” said Julia Herman, the beef cattle specialist veterinarian with the NCBA. “Once the larvae get laid into wounds, they bury into the living flesh of warm-blooded animals and this can be a super painful condition to animals or people.”

Females will mate once and males can made multiple times.

“The female will lay her eggs on the edge of a wound and the eggs will hatch in 12 to 14 hours if the temperature is around 80 degrees,” Herman said.

“A lot of this is temperature dependent, so the cycle can be as short as 30 days or as long as three to four months, depending on the temperature,” she said.

There are three larvae stages, which is the most damaging part of the fly’s life cycle.

“The larvae feed on live tissue for five to seven days and attract more flies,” Herman said. “The larvae fall from the host, bury in the ground and pupate which takes about six to eight days. Then the fly will emerge and the cycle continues.”

Stopping the lifecycle is one of the best ways to interrupt the pests from reproducing.

“The sterile fly technique remains our most powerful tool for pushing this pest back away from the border,” Johannes said. “And we are in a much stronger position today than we were this time a year ago.”

COPEG — the Panama-United States Commission for the Eradication and Prevention of Screwworm — currently produces from 100 million to 115 million sterile insects per week, the NCBA executive director reported.

“A facility at Metapa in Mexico is being retrofitted and they expect to be producing sterile flies in July,” Johannes said. “It will produce a couple million additional sterile flies per week.”

“The dispersal capabilities have been completed at our Moore site in South Texas,” she said. “And we are probably 12 to 18 months away from being able to produce sterile insects out of this facility.”

Sterilizing the flies, Johannes said, is really not the challenge — it is actually the space it takes to raise them.

“They are space and water intensive and they smell terrible,” she said. “It takes a lot of staff; it is estimated there will be 400 employees working at the South Texas facility.”

Livestock producers have some options for treating the New World screwworm if it becomes a problem in the United States.

“We used to have products registered in the U.S., but the registrations had lapsed because we had eradicated the fly,” Johannes said.

“So, one of NCBA’s top priorities since this appeared in Southern Mexico in 2024 was going to USDA, FDA and EPA to get these products back on the list,” she said. “That has happened, so now we have four products that are operating under an emergency use authorization or conditional approval to treat screwworm in cattle.”

The Screwworm Response Playbook is the resource for how a state or the federal government will respond to an outbreak if it happens in the United States.

When an outbreak occurs, the playbook identifies three types of zones.

“The infested zone is 20 kilometers in radius and it is the circle on top of the detection,” Johannes said. “Beyond that is the adjacent surveillance zone where they will do surveillance for the fly and also implement some restrictions and movement.”

Some surveillance may be required in the third zone, Johannes said, but it depends on the terrain and geography of the area.

“The third area could be small and narrow or it could be wide and expansive, depending on the conditions in that area,” she said.

Johannes encourages all cattlemen to get a premise ID.

“If you are in an infested zone during a screwworm outbreak and are moving cattle out of that zone, you will have to have individual animal ID on those animals, which requires a premise ID,” she said.

“Get better at looking at your cattle,” Herman stressed. “Eyes on the cattle is the best thing we can do for picking up a New World screwworm infestation as quickly as possible.”

Producers should monitor their cattle for behavior changes.

“Maybe the animal is isolating itself, it is not eating or it is shaking its head,” the veterinarian said.

“The cattle can have a small external wound, but have a deep, infested pocket under the skin so you have to be able to look at them closely,” she said. “Look at the creases of the animal — the ears, under the tail, between the hind legs, the udder skin folds and dehorning sites.”

There will be a smell of decay and a really pungent odor coming from the wounds.

“That is one of the distinguishing characteristics, but don’t wait for that to be the sign,” Herman said. “Train your team on what to look for, and if something looks abnormal, please call your veterinarian.”

If untreated, the veterinarian said, New World screwworm can cause death in animals in seven to 14 days.

“In younger or smaller animals, that could be quicker,” Herman said.

“There are a lot of things you can do now to help prepare for when and if New World screwworm gets here and a lot comes down to prevention and enhanced management practices,” she said.