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By Dean Ruhl
The United States Department of Agriculture confirmed the presence of New World screwworm in the United States this past week.
The dangerous pest can seriously affect livestock, pets and wildlife, and less commonly, birds and humans. With its return, Oklahoma State University Extension experts offered producers useful information.
Not a worm, but a fly
The name New World screwworm can be misleading, Rosslyn Biggs, DVM, OSU Extension beef cattle specialist, said.
They are not worms. Instead, the concern is with a specific type of fly. The fly will lay eggs in an open wound, and the resulting maggots will feed on live tissue, as opposed to more common maggots that eat dead or decaying tissue. Wounds as small as a tick bite can become infested.
New World screwworm flies look similar to other common flies, explains Jonathan Cammack, OSU Extension livestock entomology and parasitology specialist.
“We’ve got flies that are metallic green that are strongly associated with our livestock,” he said. “There is a fly that is very closely related to a house fly that only eats cow manure. Metallic-colored flies and non-metallic flies that feed on these rotting materials are there and have been there for quite some time, but they’re not screwworms,” Cammack said.
No issue with the food supply
Biggs stressed that New World screwworm is not a disease, but an infestation. Livestock affected are safe to enter the food supply after treatment. New World screwworm does not infest meat, fruits, vegetables or any other food source.
“We have no concerns related to food safety,” Biggs said. “Animals that have been infested after treatment, they are good to enter the food supply.”
Good practices reduce risk
When moving animals across state lines, Biggs emphasized having the appropriate documentation in order before traveling. A certificate of veterinarian inspection is always required, but if producers are moving animals to a destination state, enhanced requirements may be necessary.
“Naturally, the flies only have the ability to fly relatively short distances,” Cammack said. “Maybe five to 10 miles over the course of their lifespan, while that female fly is looking for a host animal to lay her eggs on. A lot of the large jumps we’ve seen over the past year and a half through Mexico have been from human-mediated movement of animals from screwworm positive areas in southern Mexico to feed lots in northern Mexico.”
Biggs recommends establishing a strong relationship with a veterinarian if producers do not already have one. Producers should also consider enhancing current biosecurity measures or adding additional ones to their operation.
“In particular, my hallmark of biosecurity is daily inspection,” Biggs said. “We want animal owners to think about that and how they can implement that. Additionally, at some point, there is likely a need to apply treatment and prevention to livestock.”
Proper animal husbandry practices can reduce risks, and inspecting vulnerable calves is also recommended. Producers should also regularly inspect fences and other working facilities.
“We need to be vigilant,” Cammack said. “Producers need to have eyes on their animals.”
Screwworm has been eradicated before
In the 1950s, the USDA began using the Sterile Insect Technique to eradicate New World screwworm from the United States. By introducing sterile blowflies into infected areas, scientists were able to push the infestation deep into Central America over almost five decades.
“We don’t want animal owners to be scared. We have options, we have treatments and preventative options in place and approved,” Biggs said. “We do encourage them to arm themselves with information.”
Cammack added, “USDA deploys a response team that’s trained in monitoring and trapping screwworms. They set up a perimeter and release sterilized flies in that area.”
Warm-blooded mammals are susceptible
New World screwworm cases often involve livestock. But in rare instances, birds, such as chickens, and humans can become infested. Most often, they enter an animal through an open wound.
“In the state of Oklahoma, we’ve been preparing here for the last 18-24 months. With that, every day for animal owners is not going to look any different,” Biggs said. “However, we are seeing additional communication and awareness that we want animal owners to be vigilant.”
Up-to-date information about New World screwworm can be found online at screwworm.okstate.edu and on the Oklahoma Department of Agriculture and Forestry website. Federal resources can be found at screwworm.gov, providing nationwide coordination.
OSU Extension uses research-based information to help all Oklahomans solve local issues and concerns, promote leadership and manage resources wisely throughout the state’s 77 counties. Most information is available at little to no cost.
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