Life History and Reproduction

           Who first discovered Onchocerca volvulus?    

     John O’Neill, an Irish surgeon, first found microfilaria in subcutaneous tissue while examining a patient from Ghana in 1874. Nineteen years later, Patrick Manson identified the adult worm and in 1893, a Zoologist named Rudolf Leuckart described the morphology of the adult form of the worm. Then in 1904, Emile Brumpt made the connection between the microfilaria in the tissue and the adult worm. Brumpt also observed that the infection of these worms tends to occur along riverbanks. Rodolfo Robles then published this “new disease” in 1917. The cause of Onchocerca volvulus was established by Breadablane Blacklock, stating that the disease of onchocerciasis is transmitted by sand flies (Cox 2014).

                                                    How does this parasite reproduce?
     Onchocerca volvulus live in human hosts from 8-12 years, sometimes even up to 15 years and microfilariae can live up to 2 years. The number of females is about doubled compared to the male population. Adults can live in various places within the human body and usually live in groups. The males can move from group to group where they then impregnate the females (Dalton 2001).
     To attract males, the females can produce a chemical substance and release it into their environment. The way the male impregnates the female is by coiling around the female with his curved area on the female genital pore. To hold the female during sex, the male uses its spicules. The sperm of the nematodes are amoeboid-like and do not have a flagella (Dalton 2001).  

       The fertilized eggs develop in 3-12 weeks into microfilariae. Once developed, the female releases the microfilariae into the host body. The species used as hosts are humans, Similium damnosum, Simulium neavei, Simulium ochraceum, Simulium metallicum, Simulium callidum, Simulium exiguum, and blackflies. One female can reproduce for 9-11 years and can release 1300-1900 microfilariae per day (Dalton). The microfilariae then travel away from the adults. They travel through blood vessels, lymphatics, skin and connective tissue, and generally settle in the skin. When the microfilariae die, they cause inflammation which can also lead to skin rashes, lesions, skin coloration and extreme itching. If the microfilariae get into the human eye and cause complications it can lead to blindness (Life-cycle of Onchocerca volvulus 2014).
      The life cycle of the Onchocerca volvulus is very complex. It involves both a definitive and intermediate host. The human is the only natural definitive host, whereas the intermediate host is a black fly, which is in the genus of Simulium, very similar to the parasite Plasmodium falciparun which is also transferred through an insect, the mosquito. These flies, that can cause blindness, require the oxygen that comes from quickly flowing river water. This is why the disease onchocerciasis is commonly referred to as “river blindness” (Truant 1998).

                                 Life Cycle image modified from Swiss Tropical and Public Health Institute.

                                 Discover who this parasite interacts with by going to the Interactions Page!