The first local infestation of New World screwworm in the U.S. in more than 30 years has been confirmed in Florida.
The Texas Animal Health Commission (TAHC) was notified of the infestation on Oct. 3 by the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (USDA APHIS). New World screwworm was confirmed in Key deer at the National Key Deer Refuge in Big Pine Key, Florida.
New World screwworms 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. Infested animals that are not treated in seven to 14 days may die.
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.
Livestock and wildlife owners are advised to immediately contact their TAHC regional office or local veterinarian if they suspect an animal may be infested with screwworm larvae.
All of the potentially affected animals are from the same Key. There have been no human or livestock cases.In the 1950s, USDA developed a new method to help eradicate screwworm, using a form of biological control, called the sterile insect technique, which releases infertile male flies in infested areas. When they mate with local females, no offspring result. With fewer fertile mates available in each succeeding generation, the fly, in essence, breeds itself out of existence. USDA used this technique to eradicate screwworm from the U.S. and worked with other countries in Central America and the Caribbean to also eradicate it there.
The return of screwworms would deal a severe blow to the ranching and hunting industries, said a Texas A&M AgriLife Extension Service veterinary entomologist at Stephenville.
According to AgriLife Extension veterinary specialist at College Station, the cost to control the pest today in cattle alone could easily exceed $500 million annually.
It was also mentioned a price tag of $1 billion would be needed annually to eradicate screwworms from their former range, should it become re-established.
Officials have blockaded the road to stop animal movement there now, but it is not known if any had moved to other areas of Florida before the discovery. They are using pesticides and releasing sterile male screwworm flies, which is the technique that finally eradicated the pest from the U.S.
The New World screwworm as it’s called is a serious pest of all mammals, including livestock, wildlife, birds and humans, though its presence is rare but possible in birds and humans.
The primary screwworm, the ‘worm’ being the larval stage of a fly, a bit larger than a housefly, is different from all other blow flies in the U.S. The difference is that it infests and feeds on living tissue in live animals. In contrast, blow flies feed on carrion and rotting meat.
The female screwworm fly is attracted to wounds or mucous tissue on animals where she lays several hundred eggs. The larvae soon hatch and live inside the wound. As the wound festers, more females are attracted and lay their eggs.
If screwworms returned, it could be the end of part-time ranching. Except for the dead of winter, stockmen would have to constantly watch their stock for ‘wormies.’ And white-tailed deer, which give birth in warm weather, and bucks in velvet with blood-engorged antlers.
The flies’ Achilles’ heel is the female’s habit of only mating one time. Once researchers discovered this fact, they could proceed with eradication strategies. The eradication program consisted of irradiating captive male flies, rendering them sterile. The sterile flies were dropped from airplanes into areas where screwworms were present. When large numbers of sterile males were released into infested areas, native females would mate with the sterile males and then lay infertile eggs. This worked, not overnight, but it did work.
The last screwworm captured in the U.S. before this recent incursion was in 1982, before today’s younger ranchers and outdoorsmen were born.
