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Published on Thursday, October 20, 2016

Eradicated Parasite Returns To US After 30+ Years

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Eradicated Parasite Returns To US After 30+ Years

Photo by: CSIRO [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons

A flesh-eating parasite, the screwworm, has returned to the United States almost 30 years after it was widely eradicated.  This new infestation was found in deer in a wildlife refuge in the Florida Keys.  Adam Putnam, the Agricultural Commissioner of Florida, says that the occurrence of screwworms should send shivers down ranchers’ spines. He still remembers the horror stories from the last screwworm epidemic. 


What are screwworms?

Screwworms are fly larvae that feed on living flesh.  The adult screwworms lay eggs in open wounds or body orifices.  In a female screwworm’s 10-30 day lifespan, she can lay up to 2800 eggs.  Once the eggs hatch, the larvae burrow like a corkscrew into the flesh in order to feed. What makes screwworms unique is that, unlike most maggots, they only feed on living flesh of warm-blooded animals.  In the last epidemic, screwworms fed on livestock, dogs, deer and even humans.  If left untreated, screwworms can be fatal. 

What happened last time? 
Throughout the United States and into Central and South America, screwworms were an enormous problem throughout the 20th century.  At one point, ranchers in the United States alone were losing over one billion dollars per year due to infected livestock. 

How did we solve it last time?
In 1950, two US Department of Agriculture employees, Edward Knipling and Raymond Bushland, came up with a plan to stop the spread of screwworms. They realized that high doses of x-ray radiation used on male screwworms damaged their chromosomes, making them sterile and unable to reproduce. The plan was to overwhelm an infected area with these sterile males to halt reproduction.  This approach was first tested in Florida and Curacao.  Thankfully, it worked.

With the initial success, a lab was opened in Florida to release the sterile screwworms by the millions.  They were released across areas in Texas, Arizona and California until the United States was deemed screwworm free in 1982. The national eradication campaign was a success. 

But unfortunately, screwworms don’t recognize national borders.  The US Department of Agriculture realized the only way to stop screwworms from causing further devastation was to partner with neighboring countries.  They established international partnerships with Mexico, Belize, Guatemala, El Salvador and Nicaragua.  Together, the countries worked to stop the spread of screwworms.  To this day, the partnership is still alive and well.  In fact, there is an area between Central and South America, the Darien Gap, that still receives weekly flyovers where sterile screwworms are being dropped.  

Why are they back and how do we get rid of them now?

After such an extensive elimination process and continued work to keep screwworms from returning, the new infestation in Florida is both devastating and confusing. The exact source is still unknown.  However, many experts point to the United States’ new relationship with Cuba as a possible source.  Cuba was not part of the original international partnership to eliminate screwworms and the species still exists in Cuba.  It is possible that they have reentered the United States through increased trade and travel with Cuba.  

Unfortunately, the original lab that created the sterile screwworms in Florida has long been closed.  Jenn Meale, the Communications Director of the Florida Department of Agriculture, explains that a screwworm barrier maintenance program has been put in place by requesting sterile screwworms from other countries and creating inspection checkpoints in and around the Florida Keys. 

Jorge Hendrichs, head of insect control at the Food Agriculture Organization and International Atomic Energy Agency, says the only way to permanently stop the new infestation is to do what we did in the 1980s.  We need to partner with Cuba and work together to eradicate screwworms from their country and ensure screwworms don’t come back and wreak havoc in the United States. 

Taking aim at other insects
After the success of the radiation technique to create sterile screwworms, scientists are looking at other options for eliminating dangerous insects.  Mosquitoes carrying the Zika or West Nile virus are of particular concern.  Oxitec, a British biotechnology company, has developed a process of inserting a gene into mosquitoes that will decrease reproduction and lead to an overall suppression of the mosquito population. They have received permission to test their genetically modified mosquitoes in certain areas of Florida.  However, this approach of altering genes in living creatures has been met with a lot of criticism. The controversial plan to eradicate mosquitoes requires a lot more science and public buy in before it can be considered. 
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Author: Ccarrell

Categories: Blogs, Animals & Wildlife

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