Answer to the Parasite Case of the Week 659: Onchocerca volvulus adult worms and microfilarie.
If you didn't already see it, check out the whole slide scanned image HERE.
In this case, you can see a large subcutaneous nodule containing the adult worms (each female with a characteristic "double barrel" uterus) and microfilariae being released into the surrounding skin.
The microfilariae are the primary source of disease, as they crawl through the skin causing intense itching and inflammatory changes. They also go to the eye and cause irreversible blindness. The latter is the reason that infection is called "River Blindness". Infection is transmitted through the bite of infected black flies (Simulium sp.) which breed in fast flowing waters.