A traveler from Tanzania who had spent a week on a safari tour presented with a large boil over his thigh which had not resolved with oral antibiotics. A small white lump popped out of the boil during the surgical incision and drainage of the “abscess”.

Microscope view – 3 mm in length

Higher magnification view of spikes on the body.

What is this 3 mm “lump” and what is the diagnosis?

[Updated 11th October 2014]

This unfortunate traveler has myiasis, which is the medical term for parasitic infestation of a mammal by fly larva. In Tanzania (and most of East and Central Africa), the most common fly that causes this condition is Cordylobia anthropophaga, also known as the tumbu fly or putzi fly. The fly lays its eggs on soil or damp clothes (usually clothes hung out to dry), and the larva – which hatch out in 2-3 days – will penetrate the unbroken skin of mammals (or humans) that they come into contact with, creating a boil. In the South American variant, the botfly (most commonly Dermatobia hominis) lays its eggs on an intermediate vector such as a mosquito, which transmits the subsequently hatched larva to humans or other mammals.

The best form of treatment is actually not surgery (and certainly not squeezing out the boil, which crushes the larva and creates more inflammation), but application of vaseline or scotch tape over the boil. This cuts out the air supply to the larva, which causes the larva to tunnel back out to the surface. Without the larva, the boil will heal by itself fairly rapidly. One useful precaution while traveling in East and Central Africa is that one should iron one’s clothes if one hangs one’s laundry out to dry.