Answer to Parasite Case of the Week 572: Tungiasis, due to the parasitic female sand flea. As Blaine mentioned, it is most likely Tunga penetrans, but in Brazil, Ecuador and Peru, there is a second species infesting humans: T. trimamillata. It's not possible to tell the two species apart from this image alone.
What we can see from this beautiful image by Dr. Maia is an anterior portion of the female Tunga flea that had been curretted from the patient's foot lesion.
Infestation with the Tunga flea is called tungiasis. From anonymous: Tungiasis "is one of our favorite words as sounds very nasty and rolls off the tongue very nicely." Indeed, tungiasis is a particularly nasty, painful, and potentially debilitating condition where the female flea burrows head first into exposed skin - often between the toes and under nail beds. Santiago reminds us that medical treatment is ineffective, and "prevention is thus the best way of controlling the disease, preventing the parasite from penetrating the intact skin. But who wants to wear shoes at the beach?"
Thanks again to Dr. Maia for sharing this case!