Onchocerca volvulus

Onchocerca volvulus is a helminth.

Disease / Pathology

Onchocerca volvulus is transmitted by the black fly (simulium) and has no periodicity.

Location in the Host

Onchocerca volvulus adults are located in subcutaneous nodules while the microfilariae are found in skin and in lymphatics of connective tissue.

Geographic Distribution

Onchocerca volvulus is found in South & Central America, and Africa.

Life Cycle

Onchocerca volvulus has the life cycle depicted below. The L3 stage of the larvae are the infective stage transmitted to the human host. The microfilariae ingested by the blackfly undergoes undoes three molts to become the L3 larvae stage that migrates to the head of the blackfly and is found in the blackfly’s proboscis.

Morphology & Diagnosis

Onchocerca volvulus microfilariae are approximately 148-355 um in length. Nuclei do not extend to the tip of the tail which is tapered.


Key identifying characteristics of Onchocerca volvulus – Illustration by W. Vientos