SAN DIEGO – Identifying a botfly infestation can be the toughest part of treating it. It’s not uncommon for travelers to return from Costa Rica, Belize, and other Central and South American countries with Dermatobia hominis infestations, but clinicians in North America are not necessarily comfortable diagnosing them or removing the larvae,, said Dr. Susan McLellan, who explained how to do so at an annual scientific meeting on infectious diseases.
©Geoff Gallice/Wikimedia Commons/CC-By-2.0Extraction of a Human Botfly larva
Clinicians here may confuse botfly infestations with infected sebaceous cysts, staphylococcal infections, cellulitis, or even cutaneous leismaniasis. To make the diagnosis, ask about travel history in patients who present with painful furuncular lesions, said Dr. McLellan, associate professor of clinical medicine at Tulane University, New Orleans.
Closer inspection of these lesions may reveal the two dark spiracles, or breathing holes, of the larvae, which are key to removing them, Dr. Mclellan added. “The larvae have to stick their little spiracles out to breathe,” she said. “You can get them to come further out by covering up these breathing holes with anything occlusive. It can be peanut butter. It can be petroleum jelly. Just cover them up until they stick themselves out more, and then you can grab them and pull them out.”
The “first smother, then pull” approach does not always work with botfly larvae because they have spines on their bodies that can hook into subepidermal tissue, Dr. McLellan noted. “Sometimes you have to make a very, very careful incision,” she said. “Do not incise the larva at all, though. Just pop it out. These lesions do not get superinfected unless you chop up the larva while they are still inside.”
Also do not bother asking patients if they were bitten by the black adult botfly, said Dr. McLellan. Adult D. hominis do not bite, but instead lay their eggs on mosquitos. “Any biting insect that flies could potentially be a carrier,” Dr. McLellan noted. “The mother botfly catches the other flying insect, dumps her eggs on it, and that other insect starts delivering them.” A single mosquito bite can transfer several botfly eggs to a human host. When the larvae hatch and burrow into the skin, they cause pain, redness, and swelling until removed.
Dr. McLellan spoke at the combined annual meetings of the Infectious Diseases Society of America, the Society for Healthcare Epidemiology of America, the HIV Medicine Association, and the Pediatric Infectious Diseases Society. She reported having no conflicts of interest.