Time-tested foe for MRSA

July 1, 2007

Green bottle fly larvae - maggots to the less squeamish - are the latest tool to be enlisted in the battle against MRSA. British physician Andrew J. M. Boulton says, "We frequently use larvae in diabetic foot ulcers, so there was no reason to believe that they would not work against MRSA."

Key Points

British physician Andrew J.M. Boulton, M.D., F.R.C.P., says, "We frequently use larvae in diabetic foot ulcers, so there was no reason to believe that they would not work against MRSA."

He says the growing presence of drug-resistant pathogens in diabetic foot ulcers prompted physicians to dust off the old treatment that was largely abandoned with the advent of antibiotics.

The observational study enrolled 13 consecutive patients with chronic foot ulcers that cultured positive for the presence of MRSA and did not have evidence of systemic disease that would require systemic administration of a drug. The larvae were applied for four days at a density of ~10 larvae/cm2 for two to eight applications per ulcer, and were protected with an occlusive dressing and padding.

Patients also were screened for MRSA colonization, with 11 of 13 screening positive on entry. They were provided a five-day self-treatment regimen for decontamination. Upon discharge, seven of 13 still screened positive for colonization, despite the fact that wound colonization had disappeared in 12 of 13 patients.

There did appear to be some wound closure over the short course of therapy, but Dr. Boulton says he hesitates to say if any factors correlate with greater or lesser success in using the larvae.

He says the initial work was more of a pilot study, insufficiently powered to yield definitive answers, although a larger study should do so.

The outcomes justified a large, randomized controlled trial comparing larvae with standard antibiotic therapy. That trial is already under way and data should become available in about a year, he says.

First-line option?

Should larvae be used only as a last resort, after antibiotics have failed?

"Absolutely not!" Dr. Boulton says. "MRSA is a result of the misuse of broad-spectrum antibiotics. We should be trying to use as few of them as possible."

He acknowledges that patients "don't quite know what to say" when he tells them what he is going to do. "But when they see the effect, they're delighted."

Dr. Boulton calls use of the maggots "microsurgery with the world's smallest surgeons." The larvae remove sloughy necrotic tissue and facilitate wound healing. Better yet, they do so without the side effects of antibiotics and at a cost of $10 to $15 a day - substantially less than the cost of drugs such as vancomycin and linezolid.

"We're also looking at the mechanism of action of how the larvae remove the MRSA," Dr. Boulton says. "It appears that MRSA is like a magnet and the larvae are like iron filings drawn to the cuticle."

It may well be that larvae are most effective at those points were circulation is poorest and a systemic antibiotic is least effective.

'Amazing' effects

Roger Weenig, M.D., M.P.H., has become an enthusiastic convert to larval therapy after experience with only a handful of patients.

The dermatologic consultant at the Mayo Clinic in Rochester, Minn., has created a protocol for hard-to-treat calciphylaxis patients in whom debridement is difficult and painful. Even a skilled surgeon will cut into live tissue and miss small bits of necrotic tissue.