New World Screwworm (Cochliomyia hominivorax) Outbreak and Treatment in Endangered Key Deer (Odocoileus virginianus clavium)
American Association of Zoo Veterinarians Conference 2017
Lara Cusack1, DVM; Samantha Gibbs2, DVM, PhD; Rebecca Shuman3, MS; Mark Cunningham3, DVM, MS, DACVPM
1Florida Fish and Wildlife Conservation Commission, Naples, FL, USA; 2National Wildlife Refuge System, U.S. Fish and Wildlife Service, Chiefland, FL, USA; 3Florida Fish and Wildlife Conservation Commission, Gainesville, FL, USA


Infesting only living tissue, the New World screwworm (NWS), Cochliomyia hominivorax, differs from other North American blow flies, which feed on decaying tissues.2 With the female capable of depositing up to 450 eggs onto a wound as small as a tick bite, NWS myiasis can quickly become life threatening and has resulted in significant economic losses in domestic livestock.2 NWS infestations capable of sustained reproduction were eradicated in the United States in 1966, with the last reported case in 1982.1,2 In September 2016, NWS infestation was documented in an endangered Key deer (Odocoileus virginianus clavium) on Big Pine Key, Florida. Primary eradication measures included biologic control through sterile fly release. Additional efforts to reduce the impact on Key deer and reduce fly numbers included euthanasia of severely affected deer, topical and oral administration of doramectin to free-roaming deer, treatment of mild to moderate infestations, and gamete preservation. Treatment included larvae removal, wound care, topical coumaphos, injectable doramectin, antibiotics, and marking for followup. Of 25 animals assessed by veterinarians, six were euthanized, 17 were treated, and two were monitored without handling. Two animals later died due to trauma and one animal required re-treatment. Treated animals were identified at 3 months post assessment with clinical resolution or improvement. While biologic control measures were most effective in reducing fly numbers and ending the outbreak, treatment proved effective for mild to moderate infestations and resulted in preservation of individuals, reduction in fertile flies, and improvement in community support for the eradication program.


The authors would like to acknowledge the staff at the U.S. Department of Agriculture/Animal and Plant Health Inspection Service, the U.S. Fish and Wildlife Service, the U.S. National Parks Service, the Florida Fish and Wildlife Conservation Commission, the Florida Department of Agriculture and Consumer Services, the Screwworm Barrier Maintenance Program in Panama, and the community of the Florida Keys for their roles in this multi-agency and community-assisted eradication program.

Literature Cited

1.  CABI Invasive Species Compendium [Internet]. Cochliomyia hominivorax (New World screwworm) datasheet; 2016 [cited 2017 February 25]. Available from

2.  Mastrangelo T, Welch JB. An overview of the components of AW-IPM campaigns against the New World screwworm. Insects. 2012;3(4):930–955.


Speaker Information
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Lara Cusack, DVM
Florida Fish and Wildlife Conservation Commission
Naples, FL, USA

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