Parasitology

Adult worms live in nodules (encapsulated by fibrous tissue) which are located over bony parts in the body. One nodule may contain several male and female worms. These nodules are palpable.

After fertilization, a female worm may produce 1300 - 1900 microfilariae (the tiny larvae) per day for 9 - 11 years. Some of these microfilariae are ingested by a female blackfly during a blood meal. A small portion of these microfilariae are not digested and are able to penetrate the stomach wall and move to the thoracic muscles of the fly where they transform in 6 - 12 days into the third stage of the larva (or L3). This L3 is the infective form of the microfilaria, which will move to the head. Here the L3 larva is ready to infect another human being during the next blood meal of the blackfly.

Most of the larvae in the human body are not ingested by a blackfly. These microfilariae will die in six months. A microfilaria has to pass through the blackfly vector to become infectious and to be able to grow into an adult worm.