Hoosier Ag Today 

Preventing New World Screwworm from Returning to the US and Harming Cattle Herds

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An adult New World screwworm (NWS) fly, which is about the size of a common housefly (or slightly larger). The name screwworm refers to the maggots’ (larvae) feeding behavior as they burrow into the wound, feeding as they go like a screw being driven into wood. The NWS maggots cause extensive damage by tearing at the hosts’ tissue with sharp mouth hooks. The wound can become larger and deepen as more maggots hatch and feed on living tissue. As a result, NWS can cause serious, often deadly damage to the animal. Photo courtesy of USDA Animal and Plant Health Inspection Service (APHIS).

If you’ve been a cattle producer for a long time, you may remember the last time that the New World screwworm harmed livestock here in the U.S. USDA is working now to prevent the pest from making a comeback.

“[USDA is providing] $165 million in emergency Commodity Credit Corporation (CCC) funding to be able to protect U.S. livestock from New World screwworm,” according to Jenny Moffitt, USDA Under Secretary for Marketing and Regulatory Programs.

The New World screwworm (NWS) is a fly that has a gory way of harming cattle. The female flies lay their eggs in open wounds or body orifices and when the larvae hatch, they burrow deep into the skin like a screw driving into wood. These NWS maggots feed on cattle’s tissue, causing much larger wounds as they go.

“We had it here in the United States in the early-to-mid 1900’s,” says Moffitt. “Then, over the course of several decades, in a very collaborative approach with Mexico and with many countries in Central America, researchers actively worked to push down that pest out of the United States, and then out of Mexico, and then through Central America and down to Panama.”

That was done through a sterilization program that eradicated screwworms in the U.S. back in 1966. But Moffitt says the pests have recently been spreading across Central America. Just last month, screwworms were discovered a cow in the southern Mexico state of Chiapas, at an inspection checkpoint close to the border with Guatemala.

“A couple of years ago, [screwworms] have started to spread into Costa Rica,” she says. “For the past year and a half, USDA has really been ramping up our work and taking that much bigger and more regional approach [to fighting off screwworms] than we have been doing for several decades.”

She says USDA is using those emergency funds to use the sterile insect technique once again to kill off the screwworm before it returns to the U.S.

“We’ve expanded our number of [sterile] flies. We were currently bringing about 90 million sterile flies a week to really increase the production and the dispersal of sterile flies,” according to Moffitt.

Because of the screwworm, imports of beef from Mexico into the U.S. have been suspended since late November.

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Recent confirmed detections of New World screwworm (NWS) throughout Mexico and Central America. Graphic courtesy of USDA APHIS.
 

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