Maggot wound therapy

Maggots might be the last thing you'd want to find in a horse's wound. But a recent study assessed the efficacy of maggot debridement therapy in a range of equine lesions and found it was beneficial in 93% of cases.

Over a four year period, Dr Olivier Lepage and colleagues treated forty-one cases (35 horses, 4 donkeys, 2 ponies ) in France and Mali.

The maggots used were sterile common green bottle fly maggots, which have been used in human medicine to clean long-standing, infected or necrotic wounds. Maggots digest fibrin and necrotic tissue, along with bacteria, and secrete proteolytic enzymes and antimicrobial agents into the wound.

Interestingly these are the same species of fly larvae that are the most common cause of fly strike in rabbits and sheep. In horses (and humans) it appears that healthy tissue is able to inactivate the proteolytic enzymes so that only diseased tissue is digested. In contrast, sheep and rabbits can not inactivate the enzymes.

Maggots were applied either directly onto the wound or retained within a polyester net containing small pieces of foam. They were kept in place with cohesive, but not occlusive, bandage – maggots need oxygen.

Between 300 and 900 maggots were used for each wound, depending on its size. They were left in place for three days. In 5 cases the response to the initial MDT was inadequate and so a second treatment was applied for a further 3-4 days.

Conditions treated included limb lacerations, deep seated foot infections and soft tissue abscesses and abdominal incision breakdown. Within just one week a favourable outcome was recorded in 38 of 41 cases. Wounds that did not respond well were those involving neoplasia or a bone sequestrum.

No more than 2 MDTs were needed in this series of cases, in contrast to other reports. The clinicians suggest that this was likely due to the light surgical debridement that was carried out in most cases in this series, before the maggots were applied.

Lepage and colleagues conclude that maggots can be recommended in horses, ponies and donkeys for debridement of wounds and for their potent antibacterial effects – including their use against difficult to control infections such as MRSA and other multibacterial resistant bacteria.

They advise against its use in cases where neoplasia is present. In this study, melanoma and squamous cell carcinoma continued to deteriorate after MDT.

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