Research on foul odors and open wounds targets flesh-eating screwworm

Jessica Metcalf, Ph.D., does work that stinks. Literally. But the Colorado State University professor’s research may be key to protecting livestock and wildlife from a flesh-eating parasite.

In a project recently funded by the U.S. Department of Agriculture, Metcalf is studying foul-smelling substances to determine what attracts the New World screwworm to its favorite meal—open wounds—so she can develop better lures for trapping this serious threat to the livestock industry. The pest was eradicated in the United States more than 50 years ago but was found in Texas in early June.

When a wound starts to smell, that’s when you know it may be infected and teeming with bacteria. Foul odors are among the chemical byproducts of bacteria, and the same smelly bacterial chemicals that cause revulsion and concern for humans attract the New World screwworm, a type of blowfly.

“We use these bacterial cues to stay away from certain things—to not eat spoiled meat, for example,” Metcalf said. “The insects are using them for a different reason. They’re like, ‘Yes, bring it, that smells like a great place to lay eggs.’”

The New World screwworm blowfly lays eggs in wounds and body openings. The maggots that emerge then feed on living tissue. It can infest any warm-blooded animal, including people and pets, although there is low risk in the U.S. Left untreated, the parasite can be deadly.

The USDA recently announced $105 million in funding for 40 projects, including Metcalf’s, to improve the country’s defenses against the New World screwworm. As of July 23, the parasite has been detected in cattle, sheep, goats and two dogs in Texas and one dog in New Mexico. Metcalf and her collaborators aim to help keep it from spreading.

Building better bait

Detection is the first step to controlling the NWS. One of the most widely used lures uses bacterial-produced smells from rotting meat, so it attracts a closely related blowfly, the secondary screwworm, which prefers a diet of dead flesh. Traps fill with the abundant secondary screwworm, making it difficult to detect the more harmful New World screwworm. Metcalf’s project will develop lures specific to the NWS using bacterial-produced smells from wounds for improved monitoring.

These bacterial-produced smells are known as volatile organic compounds, organic compounds that vaporize easily.

Metcalf’s team will distinguish between the VOCs that attract the NWS and those that attract the secondary screwworm. In other words, what is so appealing to NWS about live flesh over dead flesh, where it does not cause harm?

Blowflies also carry their own bacteria, which they use to communicate within the species. These bacteria signal to other blowflies where to find a suitable host, compounding the infestation.

Metcalf’s team will distinguish which bacteria are found on the New World screwworm versus the secondary screwworm to help design better lures for traps. Knowing what attracts the NWS could also be used to redirect it away from live hosts.

“Because we had been working on the relationship among insects, bacteria and animal decomposition for the last 15 years, and the New World screwworm evolved from a decomposer—an insect that utilizes dead flesh to raise its young—we were well set up to tackle this problem,” Metcalf said.

Metcalf’s work with the bacteria that decompose animals, including humans, has forensic science applications. She and her collaborators found the microbes present on a body can accurately determine time of death, useful information for solving crimes.

“We have gained a foundational understanding of animal decomposition at our main field site in Huntsville, Texas,” Metcalf said. “The basic science underlies tools we build for forensic science in estimating how long a person’s been dead. It turns out we can also leverage decomposition ecology, which relies heavily on blowflies and their bacterial partners, to improve surveillance and control of the New World screwworm.”

Metcalf’s team, including CSU faculty Kayla Borton and Kelly Wrighton, will use sophisticated genomic and chemical data analysis tools through a partnership with the Colorado State Microbiome (CoSMic) Network.

Network of stakeholders

Metcalf and her collaborators will enlist the help of on-the-ground volunteers, including livestock producers, veterinarians and wildlife biologists, to swab animal wounds for laboratory testing. These stakeholders will receive diagnostic results from the laboratory tests and will benefit from the solutions developed through the project. Meanwhile, Metcalf’s laboratory in CSU’s Department of Animal Sciences will compare wound bacteria and smells with dead animal samples.

To build the network of stakeholders, the research team is leveraging statewide partners, including producer associations, state agencies, CSU Extension, CSU’s Agricultural Experiment Station, and Veterinary Diagnostic Laboratories. Stakeholders will receive information about NWS, sampling supplies, and training. Project collaborators in Texas, Arizona and New Mexico will conduct similar outreach and sampling.

Tracey Goldstein, director of CSU’s One Health Institute, will coordinate outreach, training and sampling activities across the network. She said the network needs to be as wide as possible to watch for the New World screwworm because if it infests wildlife, it will be especially challenging to control.

“This particular fly doesn’t care if you’re a person, a deer, a pig or a chicken. It will infest everything, which is a little scary,” Goldstein said. “That’s also part of why it’s hard to manage it. We really need all eyes and ears out there on the ground to help figure out if and when it reaches Colorado.”

Julia Herman, beef cattle specialist veterinarian with the National Cattlemen’s Beef Association, will connect producers across the country with the research. She said producers in infestation zones are required to check every animal for wounds, and wounds must be healed before they can move livestock.

“We can’t treat our way out of this problem,” Herman said. “We have to have other ways to manage this fly, and this project provides a way that we can decrease New World screwworm fly populations.”

She added, “While the New World screwworm isn’t affecting a lot of animals, it is affecting the cattle industry as a whole, from animal welfare to transportation challenges to extra time, money and resources to find this fly’s larvae and treat the wounds. Hopefully we can take some of that stress off the producer and minimize the time and resource loss with projects like Dr. Metcalf’s.”

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