Bumps on a UK Woman's Scalp Turned Out to Be Botfly Larvae

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In a recent issue of BMJ Case Reports, doctors with Sheffield Teaching Hospitals NHS Foundation Trust and the University of Sheffield detailed a medical mystery that makes one's skin crawl.

Soon after returning from a trip to Argentina, a 50-something woman from the UK noticed two itchy bumps on her scalp. Her doctor initially diagnosed them as cysts and prescribed antibiotics.

The antibiotics didn't work. Three weeks later, the bumps had grown in size, oozing clear, odorless fluid and occasionally producing stabbing pains. She also sensed movement inside the bumps. It was time for another visit to her physician.

Photo of the patient's scalp prior to surgery. The larva's breathing hole is visible.

This time, the woman's doctor referred her to Royal Hallamshire Hospital in Sheffield on suspicion of a parasitic infection. Medical professionals familiar with her symptoms and travel history quickly determined the identity of her two unwelcome guests: botfly larvae. Botflies are predominantly found in Central and Southern America and reproduce through a peculiar and disgusting process.

"The larvae of botflies reach their hosts through a process called phoresis," the authors of the case report explain, "whereby botflies capture and deposit their eggs on a blood-feeding insect (such as a mosquito) and these eggs are, in turn, transmitted to the host during a mosquito’s blood meal. The warmth of the host’s body triggers the fly eggs to hatch, and the larvae then burrow into the subcutaneous tissue."

The process of removing the two centimeter-sized botfly larvae, each inside its own "bump burrow," was equally peculiar and ingenious. Doctors smothered the bumps with vaseline. This would seal the puncture holes through which the larvae breathe and thus force them to surface, whereupon they would fall out or could be extracted with a forceps. This method worked for one of the larvae, but the other died inside its burrow and required minor surgery to remove.

The second botfly larva, removed following surgical excision, with breathing tube intact.

Surprisingly, untreated botfly infestation usually leaves no lasting damage to the host, the authors say. Larvae typically leave their borrowed homes after 4 - 18 weeks, dropping to the soil to pupate. After moving out, the remaining wound usually heals well.

"The patient in this scenario could have waited for the botfly larvae to leave her body naturally," the authors write. "However, this was neither acceptable to the patient nor practical after one larva died in situ, and so medical intervention was required."

Source: Rhys Watkins, Mallappa Kolar and David Ralston. "Getting under your skin: botfly myiasis." BMJ Case Reports. 2019. http://dx.doi.org/10.1136/bcr-2019-229666

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