Onchocerca volvulus is known primarily as a cause of onchocerciasis; other synonyms include:
- River blindness
- Robles' disease
- Filarial blinding disease
The blackfly (Simulium spp.) that transmits the parasite lives and breeds near rivers and streams. Remote agricultural villages located in the geographic distribution are impacted most often. Onchocerciasis is a disease of the skin and eyes. In the form of river blindness, visual impairment or permanent blindness occurs often.
In Onchocerca volvulus infections, adult worms produce microfilariae that migrate to the skin, eyes, and other organs. Most symptoms are caused by the intense inflammatory response produced when microfilariae die. Frequently, nodules form in the skin around the adult worms.
WHO reports that more than 99% of those infected live in 31 African countries.34
Of note: The Carter Center has worked for several years in Latin America and Africa to eliminate river blindness through research, education, and mass drug administration (using the drug, Mectizan). Mectizan kills the parasite larvae in the human body - this stops transmission of the parasite.35
Summary of the General Morphologic Characteristics of the Microfilariae:
| Filarial Agent | Length | Width | Nuclear column |
| Onchocerca volvulus | Large (>200 μm in length)
| Large species tend to be as wide as a red blood cell (RBC), about 6-8 μm in diameter
| Moderately compact |
| Headspace | Tail | Sheath on Giemsa |
| Long | Tapered tail, flexed, no nuclei | Never present |
36. CDC/Moore. Image #1148. "This photomicrograph depicts the anterior end of a
Onchocerca volvulus microfilaria larvae, the cause of onchocerciasis, also known as river blindness." PHIL public domain. Created 1979. Accessed April 6, 2023.
https://phil.cdc.gov/Details.aspx?pid=114837. CDC/Moore. Image #1149. "This photomicrograph depicts the posterior end of a Onchocerca volvulus microfilaria larvae, the cause of onchocerciasis, also known as river blindness." PHIL public domain. Created 1979. Accessed April 6, 2023. https://phil.cdc.gov/Details.aspx?pid=1149
