Association Does Not Mean Causation, Especially When It Concerns Maggots

We were pleased to see the article by McCullough and colleagues.¹ However, the authors draw conclusions that are misleading and state opinions as facts. They¹ concluded that myiasis caused their patient’s Morganella morganii septicemia and stated that medicinal maggots can transform into an invasive species, both without supporting evidence. 

An 82-year-old man is described with a history of hypertension and peripheral vascular disease upon admittance to a rural hospital with chief concerns of respiratory distress, hypotension, fever, and a septic profile. Blood cultures were positive for M morganii, a known opportunist commonly found as normal flora in human intestinal tracts.² After observing maggots in crevices and under hyperkeratosis on this patient’s legs, the authors concluded that maggots invaded healthy tissue and were the cause of sepsis. The authors failed to recognize that extensive hyperkeratosis and papillomatosis is a common presentation associated with secondary lymphedema.³ Noninvasive maggots can migrate under this crust to feed on dead skin, debris, and bacteria. 

The authors¹ claim maggot therapy can spontaneously transform “into invasive myiasis” without giving a reference or even an identification of their own maggot’s species. There are thousands of species of flies, and some of their larvae invade live tissue.⁴ But a study of naturally occurring wound myiasis in the United States revealed 87% of those maggots to be the same species as those used medicinally, and no cases of tissue invasion were recorded.⁵ To the best of our knowledge, over the past 26 years, tens of thousands of patients have received maggot therapy without a single case yet reported of medicinal maggots invading healthy tissue. There are several potential side effects to maggot therapy and there can be serious complications from invasive myiasis, but there is no need to blame maggots for more ills than the evidence supports. 

Respectfully,

Ronald Arlen Sherman, MD, MSc, DTM&H¹; and Robyn Bjork, MPT, CWS, CLWT, CLT-LANA^2 
1BTER Foundation, Irvine, CA
²International Lymphedema & Wound Training Institute, www.ilwti.com 

Dear Authors:

We thank our colleagues for their interest in our recent article¹ and for the opportunity to clarify what we feel to be a misunderstanding of our conclusions. First, while we mention medicinal (sterile) maggot therapy, this is purely to define them as a separate form of infestation compared to a parasitic maggot infestations (myiasis). We, in fact, did not intend to criticize the use of medicinal maggots. However, given the potential of medicinal maggots transforming into a myiasis infection,⁵ we felt it prudent that readers should understand this potential phenomenon. 

The authors of the letter point out that myiasis can occur in the setting of hyperkeratosis and secondary lymphedema. We agree with this; along with poor lower extremity hygiene, our patient had hyperkeratosis and lymphedema secondary to venous insufficiency. Venous insufficiency is a known contributor to secondary lymphedema if left untreated.⁶ We agree that we should have been more explicit, though secondary lymphedema was a logical conclusion given the disease presentation and figures.

The authors of the letter state we lack proof that myiasis caused our patient’s septicemia. We do admit that this evidence would be stronger if a live larvae species was identified. We contend that we, to the best of our ability, ruled out other sources of infection given that urine and bronchoalveolar lavage cultures revealed no M morganii as well as rapid improvement of the patient’s symptoms following our treatment protocol. Further, while septicemia secondary to myiasis is rare, several occurrences exist within the literature, which were outlined in our paper.¹ 

Our article¹ and its conclusions describe the potential for myiasis to lead to systemic infection and present a treatment plan that worked in our case. We do not attempt to refute the benefit of medicinal maggots in removing necrotic tissue and believe our language on this is unambiguous. We point out that myiasis “should be considered” on differential diagnosis of septic patients receiving medicinal maggots when other causes of septicemia are not observed.¹ We include the changing behavior and distribution of flies as added evidence that health care workers should aim to improve evaluation and treatment of patients with myiasis.

In closing, we respect the opinion of our colleagues who have offered comments regarding our recent report¹ on myiasis-associated septicemia. We do believe, though, that the intent of our report was misinterpreted and we hope we have cleared up this issue for future readers.

Respectfully,

Ian Lambourne McCulloch, MRes
West Virginia University School of Medicine, Morgantown, WV