Screwworms (Diptera: Calliphoridae) in the U.S.: response to and elimination of the screwworm outbreak on the Florida Keys

Authors: Skoda, Steven; WELCH, JOHN - Animal And Plant Health Inspection Service (APHIS); Phillips, Pamela

Submitted to: Journal of Medical Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2018
Publication Date: 7/1/2018
Citation: Skoda, S.R., Welch, J., Phillips, P.L. 2018. Screwworms (Diptera: Calliphoridae) in the U.S.: response to and elimination of the screwworm outbreak on the Florida Keys. Journal of Medical Entomology. 55(4):777-786.

Interpretive Summary: Eradicating screwworms from continental North American using the sterile insect technique has provided huge economic benefit to livestock producers by eliminating the horrific effects of screwworm myiasis. But an outbreak is possible as screwworms still exist in South America and the Caribbean. After confirmation by the USDA National Veterinary Services Laboratory on 30 September 2016, an alert was issued that screwworm myiasis was found in the Florida Keys. Following existing emergency response plans, we arrived in Marathon, FL on 3 October 2016 and met with personnel from USDA Animal and Plant Health Inspection Service, the State of Florida, U.S. Fish and Wildlife Service and local officials. We familiarized ourselves with the locale, personnel in the outbreak focus on Big Pine Key and witnessed infested Key deer; screwworm adult sampling was initiated using sweep nets as flies arrived at putrid liver and the first female was collected within 1 h. Larval samples were collected for DNA analyses and to develop a Florida outbreak line to test mating compatibility with the mass produced strain. Ground release chambers for sterile screwworm releases, initiated on 11 October 2016, were placed based on analyses of satellite images. Further liver trapping showed that thirteen Keys were infested; one case, presumably through animal movement, occurred at Homestead, FL (the mainland). Ultimately thirty four release stations were placed; four located around Homestead but no further cases were collected. The final myiasis case was on 6 January 2017. Sterile fly releases ended on 25 April 2017; about 188 million sterile flies were released.

Technical Abstract: Eradicating screwworms, Cochliomyia hominivorax (Coquerel), from continental North American via the sterile insect technique has provided huge economic benefits to livestock producers by eliminating the horrific effects of screwworm myiasis. After confirmation by the USDA National Veterinary Services Laboratory on 30 September 2016, an alert was issued that screwworm myiasis was found in the Florida Keys. Following existing emergency response plans, we (JBW and SRS) arrived in Marathon, FL on 3 October 2016 and met with personnel from USDA Animal and Plant Health Inspection Service, the State of Florida, U.S. Fish and Wildlife Service and local officials. After familiarizing ourselves with the locale, personnel in the outbreak focus on Big Pine Key and witnessing infested Key deer (Odocoileus virginianus clavium Barboyr & Allen) screwworm adult sampling was initiated using sweep nets as flies arrived at putrid liver; the first female was collected within 1 h. Larval samples were collected from infested animals for DNA analyses and to develop a Florida outbreak line to test mating compatibility with the mass produced strain. Ground release chambers for sterile screwworm releases, initiated on 11 October 2016, were placed based on analyses by PLP. Further liver trapping showed that thirteen Keys were infested; one case, presumably through animal movement, occurred at Homestead, FL (the mainland). Ultimately there were thirty four release stations; four located around Homestead but no further cases occurred. The final myiasis case was reported on 6 January 2017. Sterile fly releases ended on 25 April 2017; about 188 million sterile flies were released.