New World Screwworm Outbreak and Response

infected deer

A male Key Deer infected with New World Screwworm.

Beginning October 1, 2016, Florida Fish and Wildlife Conservation Commission (FWC) began assisting with an emergency response to an outbreak of New World Screwworm in Florida’s Key deer population. Other agencies responding included the U.S. Fish and Wildlife Service (USFWS), United States Department of Agriculture: Animal and Plant Health Inspection Service (USDA-APHIS), Florida Department of Agriculture and Consumer Services (FDACS) and Monroe County.

The New World Screwworm (NWS) is a foreign animal disease caused by a species of blowfly. Infestation occurs when a female fly lays eggs within any open wound or body orifice. The larvae then feed on the living tissue of the animal, resulting in massive wounds that can become fatal. These flies and larvae can have a devastating impact on wildlife, domestic animals, and, rarely, humans.

The introduction occurred in early summer 2016, and as the outbreak progressed female flies targeted bucks that had sustained injuries during rut (mating season). Had the flies persisted into the spring fawning season they would then have targeted postpartum females and the umbilicus of newborn fawns, which would have had an even more severe impact on the Key deer population. Another concern was that this foreign animal disease could spread to peninsular Florida, where it would impact wildlife and the cattle industry.

The outbreak spread throughout the range of Key deer but most management efforts were focused on the core population on Big Pine and No Name Keys. The response for NWS had three components: limiting spread, reducing fly numbers, and the release of sterile male flies to stop fly reproduction. To prevent the spread of NWS, an animal check station was set up at the north end of Key Largo by FDACS and Monroe County.

veterinarians treat a key deer

FWC and USDA conservation veterinarians treat a Key Deer infected with New World Screwworm.

The two primary components to FWC’s response were conducting surveillance for NWS on the mainland and helping with the response efforts in the Keys. To contribute to surveillance on the mainland, FWC staff worked with their public information coordinators to spread the word to other FWC employees, hunters, wildlife rehabbers, and other stakeholders about what to do and who to contact if a suspected case of NWS was seen on the mainland. Suspect cases on the mainland were investigated by FWC and FDACS. In the Keys, staff in FWC’s Fish and Wildlife Research Institute’s Fish and Wildlife Health Program participated in response efforts by assisting with humane euthanasia of severely infested deer and the capture and treatment of deer with milder cases of the disease.

Some deer were immobilized so staff could clean the wounds, administer antibiotics and antiparasitic drugs, and then mark and release the deer. Released deer were monitored the following weeks and months to assess their recovery and survival. Euthanized deer were necropsied to determine the impact of NWS and to collect samples for chronic wasting disease testing. Also, for both euthanized and captured deer, maggots were collected for identification, and blood was collected to determine parasiticide levels.

The outbreak officially ended April 15, 2017.

This disease can have a substantial impact on deer species. By the time it was eradicated from the Florida Keys, it had killed at least 135 Key deer, with many more mortalities undetected. Because Key deer are an endangered species, the additional mortality factor would have been a threat to the population if not controlled. FWC and their partners continue to monitor for reintroduction in the Keys and the mainland.