Human loiasis is confined to the rain forest and swamp forest areas of West Africa. It is especially common in Cameroon and on the Ogowe river. Loiasis is caused by the filarial nematode Loa loa which is transmitted to humans by day-biting Chrysops flies.
Once inside the body the infective larvae develop slowly into a mature adult (the process takes about a year). During this period it lives and moves around the fascial layers of the skin. In periods of growth and development Loa loa often makes frequent excursions through the subdermal connective tissues where it is often noticed by the host. Once they reach maturity (measuring 3-3.4 cm x 0.35-0.43 mm for males and 5.7 x 0.5 mm for females) the adults mate and produce sheathed microfilariae 298 x 7.5 micrometers in size.
The worms are diurnally periodic in synchrony with their vector and once they reinfect a fly they undergo two stages of growth into infective larvae (in about 10 days time) which can then be transmitted back to humans.
Most of the pathological problems observed in people infected with Loa loa are connected to periods when the migrating adult worms appear near the surface of the skin. The worms often appear around the eye where they can be easily seen and extracted before they damage the conjunctiva.
Immune reactions to the migrating worms can also cause calabar swellings in the arms and legs. Recurrent swelling can lead to the formation of cyst like enlargements of the connective tissues around the tendon sheaths. These swellings can be extremely painful when moved. Dying worms can also cause chronic abscesses followed by granulomatous reactions and fibrosis.
I'm pretty sure I have this. Too much time spent in Nigeria and Cameroon. In fact, the place I was based in Nigeria was called Calabar (see calabar swellings above). Every time I feel something funny in my eye I run to the mirror expecrting to see a worm crawling around. Usually it's just an eyelash though.
From Mr Lucky Doubles: Here's you looking in a mirror: I think it's more than an eyelash, you host.
