Screwworm infestation went unreported for months

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Signs of screwworm infestation were reportedly seen in Florida wildlife and domesticated animals months before a biologist reported infestation to the state.

Dr. Diane Kitchen, veterinarian manager for bovine programs for the Florida Department of Agriculture and Consumer Services, said in a presentation at AVMA Convention 2017 that the first signs of the New World screwworm infestation in the Florida Keys appeared in wildlife in July 2016 as myiasis in Key deer, an endangered subspecies of white-tailed deer. In the ensuing months, veterinarians began to see signs of infestation in both owned and stray dogs and cats.

At least 20 infested deer in the National Key Deer Refuge had been euthanized by Oct. 3, 2016, when the U.S. Department of Agriculture confirmed the disease was present.

Following an effort that included releasing about 190 million sterile flies and conducting 17,000 inspections of pets and livestock, some of which were inspected multiple times, the USDA declared the pest eradicated March 23, Dr. Kitchen said. The U.S. Fish and Wildlife Service estimated about 135 Key deer were killed by the infestation, reducing the population to about 740.

Screwworms are named for their larvae, which eat the living flesh of animals. They become screwworm flies, which target wounds as egg-laying sites.

The U.S. eradicated self-sustaining screwworm populations in 1966. The U.S. and Panama maintain a sterile fly barrier at the Colombia border, keeping the flies from spreading northward from South America.

Dr. Kitchen said that releasing sterile male flies is effective in eradicating screwworms because each female screwworm fly mates only once. The effort in the Keys also involved administering treatment and preventive medication to thousands of Key deer.

Dr. Kitchen said it was lucky that the screwworm infestation occurred in an area with physical boundaries that allowed isolation of infested animals and contained minimal livestock populations. Even so, direct costs of the infestation exceeded $5 million, and indirect costs included impacts on trade.

The pets and other domesticated animals that became infested were generally those kept outdoors and those receiving less-than-ideal care. She also noted that the origin of the infestation remains to be determined, and that a better screwworm DNA library is needed.

Related JAVMA content:

Screwworm again eradicated in Florida (May 15, 2017)