APHIS Releases Epidemiology Report on New World Screwworm in Florida Keys

Dan Cattle, Florida, Industry News Release, Livestock

aphisAPHIS is releasing an epidemiology report outlining its initial findings of New World Screwworm (NWS) in Key deer from the National Key Deer Refuge in Big Pine Key, Florida. APHIS initiated the investigation to determine the origin of the screwworm fly and try to understand how it may have been introduced.

Although the investigation did not identify one specific pathway, it did help identify the most likely source of introduction including a detailed evaluation of whether fly larvae was carried on a human or an animal into the United States. This means that humans may have entered the country unknowingly infested with NWS larvae, or they may have unknowingly brought animals infested with NWS larvae. The report also states that NWS was most likely introduced in the lower Florida Keys during the spring of 2016, where Key deer provided a very suitable host for the fly to become established.

As part of its investigation, APHIS issued a questionnaire to veterinarians and animal facilities throughout the Keys to help identify the NWS infestation source.  An on-going public survey was also distributed to identify any cases of screwworm in people or pets during 2016.  No human cases were reported to local health departments and little data exists on international flights and watercraft with animals arriving in the Keys. The local Customs and Border Patrol office did not report any findings of aircraft or watercraft with suspected diseased animals.

screwworm_larvaTo gain more insight, APHIS is working with the Agricultural Research Service to attempt to genotype the fly or isolate the genetic makeup and compare it to existing fly populations throughout the world. While we continue this work to determine how NWS may have entered the Keys, the Agency and its partners are working aggressively to eliminate the pest. Since October, APHIS has worked closely with Federal, State and local partners on an aggressive screwworm eradication program in Florida.

The sterile insect technique is the most effective tool we have to eliminate dangerous flies, like screwworm. APHIS maintains a fly production facility in Panama that produces millions of sterilized flies, which allowed us to quickly bring this technology to Florida. These sterilized flies are used to prevent the spread of NWS and similar pests.  The sterile insect technique allows for sterilized flies to be released in the area where they mate with wild screwworm flies and breed themselves out of existence. This program has been used to successfully control screwworm since the 1950’s in the U.S., Mexico and Central America.

To date, we have released over 80 million sterile pupae from 25 sites both within the infected zone and the barrier zone. The last confirmed case of screwworm in Florida was January 5, 2017.  We plan to release sterile screwworm flies for the next three months until we can be sure that screwworm has been eliminated from the Florida Keys. On-going surveillance and area assessments will continue.

NWS is a serious pest of warm-blooded animals.  The NWS fly larvae (maggots) can affect livestock, pets, and people. To view the report in its entirety, click here.

Image credits: (Top right) C. macellaria adult: By EdibobbOwn work, CC BY-SA 3.0, Link

(Bottom left) Screwworm larva. 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. By John Kucharski – Transferred from en.wikipedia to Commons. Original uploader was Ellmist from http://www.ars.usda.gov/is/graphics/photos/k7576-1.htmImage Number K7576-1, Public Domain, Link