Maggot Debridement Therapy for Horses

Maggot debridement therapy has proven revolutionary for non-healing wounds that don’t respond to conventional treatment. 
Maggots debride tissue using secreted digestive enzymes and through mechanical removal of necrotic tissue.
Maggots debride tissue using secreted digestive enzymes and through mechanical removal of necrotic tissue. | Getty Images

During the Civil War, it was not uncommon for physicians to encounter soldiers with wounds that were already infested with maggots. French military surgeons reported that soldiers with maggot-infested wounds recovered more quickly than those without [Maged V. The History of Maggot Debridement Therapy, University of Nevada Reno School of Medicine’s Department of Pathology, vol XXXIV, number 1, Spring 2023]. The doctors noted that only necrotic tissue was targeted by the maggots, and their debridement occurred without hemorrhage.  

Many Civil War surgeons began using maggots to clean gangrenous wounds, with improved survival rates. This benefit was also identified during World War I upon treatment of two soldiers with fractures and wounds that were infested with blowfly maggots. Instead of pus, the wounds filled with granulation tissue and the soldiers did not develop sepsis or fever. Odors disappeared by the first re-dressing, and cases of chronic osteomyelitis healed within six weeks. In the 1930s, maggots were sterilized to improve results in wound care. 

Resurgence of Maggot Debridement Therapy

With the discovery of penicillin in the 1940s, maggot debridement therapy (MDT) fell by the wayside. The inevitable formation of antibiotic resistance in bacteria stimulated a resurgence in MDT that has been FDA approved since 2004. Implementation of this ancient wound care method has proven revolutionary for non-healing wounds that don’t respond to conventional treatment. 

It is important that the maggots—Phaenicia (Lucilia) sericata—are sterilized by “disinfecting their external surface of the eggs with a non-toxic antimicrobial disinfectant like sodium hypochlorite.” The larvae hatch in a sterile container of sterile culture media, then are placed on wounds. 

Maggot Debridement Methods

There are a couple of placement options: 

Free-range method: Wound edges are covered with adhesive to prevent maggot escape by holding a hydrocolloid dressing in place. About 10 larvae per square centimeter of wound area are placed within a nylon chiffon dressing and covered with moist gauze and an air-permeable dressing covered with gauze. Dressings are changed every 2-5 days to include flushing away the larvae and replacing maggots and a similar dressing. This process is repeated for up to 10 weeks, depending on wound size. 

The biobag method: This method is similar to the free-range option except a biobag is used rather than a nylon chiffon dressing. This option is not as cost-effective and is less effective in healing results than the free-range method. 

How Maggot Debridement Works

Maggots debride the tissue using secreted digestive enzymes—proteinases and lipases—and through mechanical removal of necrotic tissue with their mouth hook and spicules and their roughened bodies. They also disinfect the wound by removing microorganisms that invade necrotic tissues. In addition, they release antimicrobial peptides that target various bacterial types, including antimicrobial-resistant MRSA, Streptococcal sp., Pseudomonas and Acinetobacter. Bacterial organisms are destroyed in the hindgut of the maggot larvae. 

In another benefit, the maggots secrete allantoin, ammonium bicarbonate and urea to increase tissue oxygenation and granulation tissue formation as well as increasing wound pH to an alkaline environment that optimizes serine proteinase and metalloproteinases.  

Chymotrypsin-like serine proteinase break downs laminin, fibronectin and collage types I and II. Non-trypsin-like serine proteinase and metalloproteinases break down fibrin clots. 

Removal of extracellular matrix components through proteolytic enzymes is helpful to healing through debridement. To add to wound healing components, angiogenesis increases following MDT as does epithelial growth once the wound fills with granulation tissue. One additional benefit comes from both maggot secretions and their movement across a wound that triggers release of cytokines (IFN-y and IL-10) by the host’s immune system.  

Potential Side Effects

While considered a very safe method of wound care, MDT can elicit side effects, such as pain as maggots move in the wound. Such discomfort is managed well with NSAIDs. In humans there are reports of possible flu-like symptoms—such as a fever—or secondary infections. It is contraindicated to use MDT on patients with bleeding disorders, those taking anti-coagulation medicine, or if large blood vessels, organs or body cavities are exposed. In some cases, it is possible to just use fewer larvae per square centimeter of wound area. 

For more detailed information, check out this publication: Naik, G.; Harding, K.G. Maggot debridement therapy: the current perspectives. Chronic Wound Care Management and Research 2017:4; pp. 121-128; https://www.dovepress.com/getfile.php?fileID=38668]. 

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