New World Screwworm Hits Mainland
January 13, 2017

The U.S. Department of Agriculture's Animal and Plant Health Inspection Service confirmed the presence of New World screwworm (Cochliomyia hominivorax) in a stray dog near Homestead, Fla. The dog was isolated and his infested wounds were treated. Federal and state officials have started active surveillance in the area.

This is the first confirmed case on Florida's mainland. Screwworm was first confirmed on Oct. 3, 2016, in key deer from National Key Deer Refuge on Big Pine Key, Fla. This initial presence of screwworm was the first local detection in the United States in more than 30 years and Florida's Commissioner of Agriculture, Adam Putnam, declared an agricultural state of emergency in Monroe County, Fla.

Since October, 13 Keys had known infestations mostly in the key deer population, with five confirmed infestations in domestic animals. Animal health and wildlife officials at the state and federal levels have been working aggressively to eradicate this pest. Extensive response efforts have included fly assessments to determine the extent of the infestation, release of sterile flies to prevent reproduction and disease surveillance to look for additional cases in animals. Officials have received significantly fewer reports of adult screwworm flies in the area and fewer cases of infected key deer. To date, fly assessments have been conducted on 40 Keys. USDA has released more than 80 million sterile flies from 25 ground release sites on 12 islands and the city of Marathon. The initial epidemiology report on the Florida Keys infestation may be viewed at

Residents who have warm-blooded animals (pets, livestock, etc.) should watch their animals carefully. No human cases have been reported in Florida. Using fly repellents and keeping skin wounds clean and protected from flies can help prevent infection with screwworm in both people and animals.

New World screwworm are fly larvae (maggots) that can infest livestock and other warm-blooded animals, including people. They most often enter an animal through an open wound and feed on the animal's living flesh. While they can fly much farther under ideal conditions, adult flies generally do not travel more than a couple of miles if there are suitable host animals in the area. New World screwworm is more likely to spread long distances when infested animals move to new areas and carry the pest there.