Tag Archive: Confirms

APHIS Confirms New World Screwworm in Dade County Dog

APHIS Confirms New World Screwworm in Dade County Dog


Screwworm larvae. Source: Foreign Animal Diseases “The Grey Book” USAHA

The United States Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) confirmed the presence of New World screwworm (Cochliomyia hominivorax) in a stray dog near Homestead, Florida. 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 October 3, 2016 in Key deer from National Key Deer Refuge on Big Pine Key, Florida. 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, Florida.

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 over 80 million sterile flies from 25 ground release sites on twelve islands and the city of Marathon. The initial epidemiology report on the Florida Keys infestation may be viewed at https://www.aphis.usda.gov/stakeholders/downloads/2017/nws-epi-report.pdf.

Life cycle of New World Screwworm from Fernandez and White, 2010. Investigation into Introduction of New World Screwworm into Florida Keys

Residents who have warm-blooded animals (pets, livestock, etc.) should watch their animals carefully. Florida residents should report any potential cases to 1-800-HELP-FLA (1-800-435-7352) or non-Florida residents should call (850) 410-3800.  Visitors to the area should ensure any pets that are with them are also checked, in order to prevent the spread of this infestation.

While human cases of New World screwworm are rare, they have occurred, and public health officials are involved in the response. No human cases have been reported in Florida. 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.

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.

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 flies in infested areas. When they mate with wild 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 eradicate it there as well. Today, USDA and its partners maintain a permanent sterile fly barrier at the Darien Gap between Panama and Colombia to prevent the establishment of any screwworm flies that enter from South America.

For more information on this subject, use the following links:

USDA Confirms Screwworms in the Florida Keys

Investigation into Introduction of New World Screwworm into Florida Keys

APHIS New World Screwworm Fact-sheet



Author: admin – webmaster@ifas.ufl.edu


Permanent link to this article: http://franklin.ifas.ufl.edu/newsletters/2017/01/13/aphis-confirms-new-world-screwworm-in-dade-county-dog/

USDA Confirms Screwworms in the Florida Keys

USDA Confirms Screwworms in the Florida Keys

Key deer buck killed by an infestation of screwworms. Credit: Samantha Gibbs, U.S. Fish and Wildlife Service.

Key deer buck killed by an infestation of screwworms on Big Pine Key. Credit: Samantha Gibbs, U.S. Fish and Wildlife Service.

Screwworms were eradicated from the Southeast back in 1959.  This week USDA’s Animal Plant Health Inspection Service (APHIS) confirmed the presence of New World Screwworms Cochliomyia hominivorax in three deer in the Florida Keys.  At this point, APHIS believes the infestation is isolated to Big Pine Key and No Name Key, but the USDA is moving forward with additional surveillance, fly trapping in the region, as well as the release of sterile flies to stop the spread of this pest.  The Florida Department of Agriculture (FDACS) has established an Animal Health Zone in the keys, with a checkpoint at mile marker 106 to check all animals coming out of the keys for screwworms.

“The screwworm is a potentially devastating animal disease that sends shivers down every rancher’s spine. This pest poses a grave threat to wildlife, livestock and domestic pets in Florida. 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 to protect our residents, animals and wildlife by eliminating the screwworm from Florida. The public’s assistance is crucial to the success of this eradication program.”  Florida Commissioner of Agriculture Adam Putnam

Screwworm larvae. Credit: Heather Stockdale Walden, University of Florida

Screwworm larvae. Credit: Heather Stockdale Walden, University of Florida


New World Screwworms also called Primary Screwworms are actually fly larvae (maggots) that feed on open wounds of livestock, wildlife, pets, and even on rare occasion people.  The adult screwworm fly is slightly larger than a common house fly, but has large orange eyes and a dark blue metallic body.  The adult flies lay their eggs on open sores, wounds, navels of newborn animals, or mucous membranes.  The maggots hatch-out within a day and feed on the living flesh of the host animal for five to seven days before leaving the animal and tunneling in the ground. The screwworms grow to a length of up to 2/3 of an inch before leaving the host animal wound and pupating in leaf litter or the soil surface .  The adult flies emerge from the ground in 7-10 days, mate only once, and complete the 24 day life-cycle.  Unlike other flesh-eating blow-flies, screwworm flies only lay their eggs on living flesh wounds. Left untreated, infected animals may perish from toxicity build up or secondary infections after 7-14 days. This was a devastating insect pest for the Florida Cattle industry in the 1950’s, before USDA developed the eradication method of releasing sterile male flies.  Because the female flies mate only once, the release of sterile male flies is a very effective tool to significantly reduce populations.

With screwworm flies present, any open wound from castration, dehorning, branding, shearing or clipping, barbed wire fences, or other causes can attract the adult flies to lay their eggs.  The most obvious sign of infestation is a significant change in the appearance of a wound.  The wound will become more enlarged and much deeper with noticeable drainage, which can attract additional flies.  It is difficult to actually see the screwworms in the early stages of feeding, but as many as 200 maggots may be found in a single wound.  Infested wounds smell rotten and will often have bloody discharge. Wounds that are not healing properly, or are producing excessive drainage should be inspected for screwworms.

Adult screwworm fly. Source: Foreign Animal Diseases "The Grey Book" USAHA

Adult screwworm fly. Source: Foreign Animal Diseases “The Grey Book” USAHA

Be on the Lookout

It is important that every livestock producer, pet owner, hunter, and wildlife enthusiast in Florida be on the lookout for this pest. Though adult flies generally do not fly more than a few miles in search of host animals, they can fly much farther if necessary.  Hurricanes have been known to bring other invasive pests to Florida.  There is potential for this pest to be spread as Hurricane Matthew blows through week, or by other storms in the future.  The more likely spread of this pest will come with animal movement.  This is why FDCAS has set up the roadblock to check pets and animals coming into mainland Florida from the keys.  This is just one more reason why it is important for livestock producers to quarantine new animals that are purchased or moved to an operation for observation, before adding them in with primary herd.

While this is currently a very isolated issue, way down in the Florida Keys, it is important that animal owners in Florida are aware of the signs and symptoms from this potentially devastating pest.  Livestock producers, and pet owners should report any potential cases to 1-800-HELP-FLA (1-800-435-7352) and consult with your veterinarian for wound treatment.  Non-Florida residents should call (850) 410-3800.

Sources of information used for this article:



Author: Doug Mayo – demayo@ufl.edu

Lead Editor for Panhandle Ag e-news – Jackson County Extension Director – Livestock & Forages Agent. My true expertise is with beef cattle and pasture management, but I can assist with information on other livestock species, as well as recreational fish ponds.

Doug Mayo

Permanent link to this article: http://franklin.ifas.ufl.edu/newsletters/2016/10/08/usda-confirms-screwworms-in-the-florida-keys/