Targeting Potentially Deadly Parasites In Unique Research Facility

Consider the screwworm's nasty business. Adult flies lay eggs near warm-blooded animals' wounds. Eggs hatch into larvae, or maggots, that feed and grow in wounds until they drop off, pupate in soil and start the cycle anew.

It's not pretty. Untreated screwworm infestations can kill a grown steer in under a week. Before being eradicated from the United States in the late 1970s, screwworms devastated the southern U.S. livestock industry, costing hundreds of millions annually. And wherever there are screwworms, there are a few human infestations.

Entomologists operate the world's only screwworm research rearing facility at the USDA Agricultural Research Service's Midwest Livestock Insects Research Unit at the University of Nebraska. They raise the critters to find ways to identify, control and, ultimately, eliminate them. Their research supports international screwworm eradication efforts.

"The only way to control a population is to understand it so you have to raise it. If you understand it, you can learn its weak links and how to control it," said Steve Skoda, who studies screwworms along with colleague Dennis Berkebile. Both are adjunct faculty in NU's Institute of Agriculture and Natural Resources.

Such understanding led the team to develop a simple, fast and accurate test that can be used worldwide to identify suspected screwworms.

This ELISA, or enzyme-linked immunosorbant assay, works like a home pregnancy test. "You just squash a fly, larva, pupa, egg or fly part, blot it on paper and apply a couple of substances. If it turns blue, you?ve got a screwworm. You're done in three hours," Skoda said. The test is easy to use and more than 99 percent accurate.

Previously, suspects had to be shipped to a laboratory for initial identification. That meant a long, anxious wait for officials who might have to launch expensive measures to quell re-infestation if the suspect proved to be a screwworm.

"This ELISA technique is going to help the entire program and save lots of money," said Gus Thomas, head of USDA"s Midwest Livestock Insects Research Unit.

Researchers also devised ways to track screwworm origins at the request of the United Nations' Food and Agriculture Organization and USDA's Animal Plant and Health Inspection Service, which heads eradication enforcement. Skoda adapted genetic fingerprinting techniques to distinguish different screwworm strains and origins. Knowing the origin is important to tracking and controlling infestations.

A technique for freezing and preserving screwworm eggs was developed at the facility, and is being refined to make it reliable enough to use at the international screwworm rearing station in Mexico. This station produces sterile flies that mate with wild females that produce no offspring, so a population gradually disappears.

"This is very painstaking, long-term research," Thomas said. "It hasn't been done with many insects."

USDA's screwworm research and rearing station at the University of Nebraska is a certified biologically secure facility --nothing gets in or out without precautions. Alarms guard sealed doors. Entry requires identification and changing into clothes that are left behind before showering out. Research is conducted under strict quarantine.