May 15, 2017


 Screwworm again eradicated in Florida

Posted April 26, 2017

New World screwworm, a deadly pest of warmblooded animals, is again removed from the United States after an eradication campaign in and near the Florida Keys.

Most of the animals known to have been killed during the infestation with screwworm fly larvae, which eat living flesh of infested animals, were Key deer, an endangered sub­species of white-tailed deer. Small numbers of other animals also were affected, including at least three dogs, two cats, a pig, and a raccoon with confirmed infestations, according to information from the Florida Department of Agriculture and Consumer Services.

Diane Borden-Dilliot, a spokeswoman for the U.S. Fish and Wildlife Service during the screwworm response, said the service estimates 135 Key deer were killed by infestation, reducing the population to about 740. About 125 of those killed were bucks, which were in rut during the infestation and had wounds that made them more susceptible to infestation.

Screwworm flies target open wounds and mucous membranes as egg-laying sites.

Borden-Dilliot, citing a refuge biologist, said the Key deer population had been rising prior to the screwworm infestation, and the deer were in good condition.

Dr. Jack Shere, the U.S. Department of Agriculture’s chief veterinarian, said in a March 23 announcement from the USDA Animal and Plant Health Inspection Service that the eradication effort involved the release of 154 million sterile flies, 17,000 animal inspections, and about 700 hours of surveillance.

Dr. Shere thanked collaborating partners for their tireless work that “has allowed us to eliminate New World screwworm from the United States once again.”

(Courtesy of USDA)

The sterile flies are effective because a female screwworm fly mates one time. They have been used to eradicate screwworms in North America and Central America, and the U.S. and Panamanian governments work together to produce about 2 billion sterile pupae each year and maintain a barrier against screwworm fly entry to Central America at the Panama-Colombia border, APHIS information states.

In backcountry areas of the Florida Keys, the Fish and Wildlife Service built bins along deer trails, filled them with sweet feed mixes, and lined the edges with paint rollers that spread a topical antiparasitic drug onto the necks and chests of feeding deer, according to Borden-Dilliot and FWS information. In neighborhoods, the service found that doughnut holes were the best medium to deliver the antiparasitic doramectin to deer, which were marked with livestock paint when they received a dose.

The APHIS announcement states that no screwworm infestations have been reported since Jan. 10, but, at press time, the agency planned to continue releasing sterile flies through April 25.

Self-sustaining screwworm populations were eradicated in the U.S. by 1966, although reinfestations occurred through 1982, and two isolated infestations occurred in dogs in 2007 and 2010, USDA information states. Both dogs had traveled to or through Florida.  

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