Modified Medical Maggots

Modified Medical Maggots
May 13, 2016

And now for things that make you go “Blugh!”

Maggots inspire a gut-churning reaction. Seeing them out in nature causes us to wrinkle our noses, and bad slasher flicks use them as a visual cue for fear and disgust.

But for some people with wounds that just will not heal on their own, maggots genetically modified by NC State University entomologist Max Scott could hold the key to the healing they need.

In a proof of concept study, Scott, along with colleagues at NC State and New Zealand’s Massey University developed green bottle fly maggots that can produce a human growth factor to help tissues regenerate in healing wounds.

Doctors have been using maggots to treat wounds for thousands of years. Mayans and Aboriginal Australians both used them, and occasional reports of medical maggots have cropped up in the French Foreign Legion, the Confederate Army and allied troops in World War I as useful by field surgeons. 

The reason is that some species of fly larvae only eat dead flesh, so they can clean out the poisonous necrotic tissue and leave a clean wound to heal as it should.

Maggot Debridement TherapyToday, doctors call it maggot debridement therapy (MDT), and it is approved by the FDA to clean wounds. The maggots eat dead flesh, prevent invading bacteria from forming a biofilm and sometimes they even secrete chemicals that can disinfect a wound. Maggots are also cheap, so if the therapy works, then it could be an option where medical procedures are expensive or unavailable.

The trouble is that some wounds, like diabetic foot ulcers do not heal well on their own. The molecular machinery is just not in place to make these wounds heal: low blood flow and little feeling. And clinical trials of MDT have not conclusively shown that the maggots can actually promote tissue regrowth and healing.

That’s where Scott’s maggots come in. They are genetically modified to produce something called human platelet derived growth factor-BB (PDGF-BB). PDGF-BB is made by human blood and stimulates cell growth and survival in an open wound.

The goal was for the modified maggots to create and secrete—the polite word for ooze out—PDGF-BB as they clean out a wound. Scott and his colleagues used sort of a trial-and-error model to study what conditions could get the maggots to release PDGF-BB.

Heating the maggots up influenced them to make PDGF-BB, but the researchers found PDGF-BB in the maggots themselves; not in their ooze.

The researchers then adjusted the maggots’ diet and when they did that, they got the oozy results they were looking for. When the maggots were fed a diet that did not include the antibiotic tetracycline, they excreted and secreted plenty of PDGF-BB.

So if you’re keeping score at home, the green bottle fly maggot—who naturally subsists on a diet of dead flesh and is itself genetically modified—is picky enough that it won’t do what you want unless you feed it an antibiotic-free diet.

This study, again, is a proof-of-concept. Scott and his colleagues wanted to show that they could create a maggot that produces a human growth factor to support wound healing. The maggots would still need to undergo many more studies and clinical trials before becoming a treatment we could see in the hospital every day.

But if they do become an effective treatment for tricky, slow healing wounds, millions of people could benefit. There are more than 29 million people in the United States with diabetes and according to the American Podiatric Medical Association, roughly 15 percent of them will develop a foot ulcer.

And if these maggots can be produced cheaply, they could provide valuable wound healing to people all over the world.

So while many of our stomachs churn at the sight of these tiny fly larvae, maybe we have been giving them a bad rap. If they can save a foot or a life by chowing down, who are we to turn up our noses?

A paper describing this work was published in the journal BMC Biotechnology.

—Daniel Lane

Daniel Lane covers science, medicine, engineering and the environment in North Carolina.