Florida officials battling New World screwworm outbreak in the Keys

November 8, 2016

The worms, affecting Key deer as well as domestic pets, haven't been spotted in the U.S. since 1960.

Tusklike mandibles protruding from the screwworm larva's mouth rasp the flesh of living warm-blooded animals. A wound may contain hundreds of such larvae. USDA photo by John Kucharski.

The U.S. Department of Agriculture's Animal and Plant Health Inspection Service (USDA APHIS) has confirmed cases of New World screwworm in Key deer from a wildlife refuge in Big Pine Key, Florida, according to a release from the Florida Department of Agriculture and Consumer Services. It is the first local infestation in the United States in more than 30 years.

New World screwworms are fly larvae that can infect livestock and other warm-blooded animals, including pets and humans, according to the Florida Department of Agriculture and Consumer Services. They most often enter an animal through an open wound and feed on the animal's living flesh. While the adult flies can fly farther in ideal conditions, they generally don't travel more than a few miles if there are suitable host animals in the area. Spread is more likely to occur over long distance when infested animals move to new areas and carry the pests with them.

Almost any type of wound can become infested with screwworm larvae, including those caused by feeding ticks, castration, dehorning, branding, shearing, barbed wire fences and even shedding of antler velvet in deer. The navels of newborn mammals can also become infested, the USDA says.

Clinical signs in deer, pets and livestock are the same. Adult flies lay their larvae in the wound of an animal where the larvae then burrow into the flesh and feed. As larvae feed, the wound gradually enlarges and deepens. An infested wound also gives off an odor and bloody discharge, the USDA states. Even if the actual wound on the skin is small, it can have extensive pockets of screwworm larvae beneath it. Feeding screwworms enlarge the wound and attract additional female flies, which deposit more and more eggs in the wound. After feeding for several days the larvae reach the pupation stage, when they drop off of the animal to the ground and complete their transformation into adult flies.

The agencies are urging pet owners to take care in checking their pets for wounds or sores and any suspected cases should be seen by their veterinarian immediately.

In response to the infestation, Florida Commissioner of Agriculture Adam H. Putnam has declared an agricultural state of emergency in Monroe County.

“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,” Putnam says in the release. “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. We will work with our partners on the federal, state and local level. … The public's assistance is crucial to the success of this eradication program.”

On October 3, samples from three Key deer were confirmed positive, while other deer from the same refuge as well as a few pets in the local area that also exhibited signs of screwworm infestation over the last two months, though no larvae testing was done in those cases, the release states. All of the potentially affected animals were from the same area of Big Pine and No Name Keys.

After the October 3 announcement adult screwworm flies were detected in six other keys: Big Torch Key, Middle Torch Key, Little Torch Key, Cudjoe, Ramrod and Summerland. Screwworm infested Key deer were also observed on Summerland.

Officials at both the state and federal level are working together address and eradicate the infestations. In addition to public education and surveillance, these efforts include the release of sterile flies, a scientifically proven method to achieve screwworm eradication, according to the USDA. The agency is increasing sterile fly production and evaluating additional sites for release.

State and federal officials are asking residents with warm-blooded animals to watch their animals carefully and seek veterinary care for open wounds, then report any potential cases to 1-800-HELP-FLA (1-800-435-7352); non-Florida residents should call (850) 410-3800.

For more information, visitFreshFromFlorida.com/screwworm.