Bot fly, shortly before removal
Image: Wakamatsu and P T P Pierre-Filho*
is a human bot fly found in Brazil and other parts of South America. These bot flies capture other insects, often mosquitoes and glue their eggs to the abdomen of the mosquito. The bot fly larvae rest inside the eggs fully developed. The trigger to hatch is a sudden increase of warmth such as when the mosquito lands on a warm mammal. The bot fly larva crawls off the mosquito and onto its host. It will burrow into the skin to feed on tissue and fluid, often using a hair follicle or the puncture left by the mosquito mouthparts to enter the skin. Occasionally, the larva will hatch near the eye and burrow into the eye. In addition to the distress, the bot fly larva can damage sensitive portions of the eye and impair vision. It is important to remove the bot fly as soon as possible.
Wakamatsu and Pierre-Filho* reported a patient with a bot fly in the eye. Unable to grip the larva to remove it with forceps, they gave the patient ivermectin, an antiparasitic medicine that affected the behavior of the bot fly larva. Bot fly larvae have a ring of spines that grip the skin and keep the swelling tissue from forcing them out of the wound. Under the influence of ivermectin, the bot fly larva released its grip on the skin. The swelling forced the larva out of the wound just enough to enable doctors to grasp it with forceps and extract it in one piece. The alternative would have required surgery to make an incision to remove the larva. In this case, quick thinking doctors successfully removed the bot fly before it could cause major damage.
*T H Wakamatsu and P T P Pierre-Filho. 2006. Ophthalmomyiasis externa caused by Dermatobia hominis: a successful treatment with oral ivermectin. Eye 20: 1088–1090.
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