New World Screwworm

New World Screwworms have only been found in North and South America. (Photo courtesy of the USDA-ARS)

By Barry Whitworth, DVM

In October 2016 the United States Department of Agriculture confirmed the presence of screwworms in the Florida Keys. The initial case was found in a Key deer.

In January 2017 the public was informed of a dog in Homestead, Fla., that was infested with screwworms. This was the first case reported on the mainland in many years. During the 2016 outbreak, the USDA confirmed 16 cases of screwworm infestation in animals. All the cases were detected in the state of Florida.

Previous to the 2016 outbreak, the last case of screwworm infestation reported by the USDA occurred on Aug. 30, 1982. Since 1982, only sporadic cases of screwworms have been diagnosed, but these were animals or people that were infested in another country and then entered the United States. The last official diagnosed case of screwworms in Oklahoma occurred in 1976.

New World Screwworms have only been found in North and South America. According to the USDASince they have been eradicated from the United States and several other countries, they are now only found in South America and five Caribbean countries. The adult flies are slightly larger than the common housefly. They have orange eyes and a blue green body that has three stripes down the back. The females typically mate once and lay their eggs along the edges of an open wound or in the mucous membranes (mouth, nose, ears) of an animal.

When the eggs hatch, the larvae burrow into the host flesh and feed on living tissue and fluids. Wounds attract more flies, which compounds the problem. Once the larvae mature, they drop to the ground, burrow into the soil, and begin the pupal stage. In a few days, the adult flies emerge to repeat the life cycle.

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