"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

November 1, 2010

November 1 - Onchocerca volvulus

Onchocerca volvulus is a filarial nematode parasite of humans that causes the disease river blindness or onchocerciasis, primarily in Africa. These nematodes are transmitted by black flies, which release the larval nematodes with their saliva when they take a blood meal. The larvae mature in the human's subcutaneous tissue and mature in nodule structures. Females will produce over a thousand microfilarial larvae per day - these tiny larvae circulate in the blood, waiting to be picked up by another black fly. Although the mature worms can live in the host for over a decade, it is the larvae that truly produce the disease symptoms - and more specifically, it is their endosymbiotic Wolbachia bacteria that cause the distress. When microfilariae die and begin to degrade, the surface proteins that these bacteria produce cause the human immune system to react quite violently - and this can cause both severe skin issues as well as cause the cornea to become opaque, thus producing the characteristic blindness. Ivermectin, an antihelminthic drug is very effective against this disease.

Image is from this website.


  1. " larvae " " microfilariae" "cercariae"
    all those names mean unmature parasites?

  2. Yes, but they are not equivalent. Microfilariae are specific to filarial nematodes. Cercariae are stages in the life cycle of trematodes.

  3. Can they be found in North america