Deer and possibly some pets in the Florida Keys have been infested with screwworms, which have not been widely present in the U.S. since the 1960s.
Officials with the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service warned in October that the New World screwworms found on Big Pine Key can infest all warmblooded animals. In an announcement, Florida Commissioner of Agriculture Adam H. Putnam said, “The screwworm is a potentially devastating animal disease that sends shivers down every rancher’s spine.”
“It’s been more than five decades since the screwworm last infested Florida, and I’ve grown up hearing the horror stories from the last occurrence,” he said in the announcement. “This foreign animal disease poses a grave threat to wildlife, livestock and domestic pets in Florida.
“Though rare, it can even infect humans. We’ve eradicated this from Florida before, and we’ll do it again.”
Donna L. Karlsons, a spokeswoman for APHIS, provided a statement in early October that more than 40 Key deer had been euthanized in recent months because of concerns about possible larval infestations, but only one of those deer was confirmed to have been infested with screwworms. A separate announcement from state agriculture authorities indicated samples from at least three deer were positive for screwworms, and other deer and some pets had clinical signs of infestation over the preceding two months, although no larvae were collected or tested.
The confirmed cases were in the National Key Deer Refuge on Big Pine Key, and the suspected infestations were on Big Pine Key and the neighboring No Name Key, according to state and federal information.
On Oct. 3, Putnam declared an agricultural state of emergency in Monroe County, which comprises the Florida Keys and the state’s southwestern tip. APHIS officials warned that people should check their animals and report possible infestations.
“While human cases of New World screwworm are rare, they have occurred, and public health officials are involved in the response,” the announcement states. “For more information about this disease in humans, please contact your local public health department.
“Using fly repellents and keeping skin wounds clean and protected from flies can help prevent infection with screwworm in both people and animals.”
Screwworms are fly larvae, or maggots. Female flies tend to lay eggs at the edges of wounds or on mucous membranes, where the larvae eat the living flesh, Karlsons wrote. Clinical signs of infestation include draining or odiferous and enlarging wounds.
“Larvae may be visible, and minor movement within a wound may be evident,” she wrote. “Veterinarians should be extremely vigilant in examining pets for any wounds or lesions.”
Infestations can be fatal if the victim is not treated.
Florida agriculture officials established a quarantine area for animals starting from the southern coastal border of Key Largo Island and an animal health checkpoint where northbound animals would be given health checks to keep screwworms from spreading. Adult flies typically travel no more than a few miles when host animals are available, and screwworms are more likely to spread through travel by infested animals, according to APHIS.
The APHIS announcement indicates state and federal agencies planned to trap flies to measure the extent of infestation, release sterile male flies to prevent reproduction, and look for additional infestations in animals.
The USDA eradicated self-sustaining screwworm populations in the U.S. in 1966 and worked with officials in Mexico to eliminate infestations there. Mexico was declared free from screwworms in 1991, and the USDA has since worked with Central American countries to eradicate screwworms all the way to the Darien Gap between Panama and Colombia.
The USDA and partner governments raise sterile flies in Panama to maintain that barrier. Karlsons wrote that the same facility was producing flies for use in the Keys, with an optimum release of 2,250 sterile flies per square mile every week.
“We are preparing to release the initial round of flies early next week and will continue to release flies in the control area for the coming weeks,” she wrote in early October. “No exact timeline is available because we’re still determining the exact extent of the infestation.”
Screwworms also entered the U.S. on dogs traveling from Trinidad and Tobago in 2007 and Venezuela in 2010. Both dogs spent time in Florida, and one traveled to Mississippi. Sites where the dogs were known to have traveled were disinfected to destroy larvae and prevent spread of the pest.
Screwworms live in most of South America and five Caribbean countries, APHIS information states.
Related JAVMA content:
APHIS plans actions on cattle fever ticks, screwworms (April 1, 2015)