Encyclopedia of Parasitology

2016 Edition
| Editors: Heinz Mehlhorn

Onchocerca volvulus

Reference work entry
DOI: https://doi.org/10.1007/978-3-662-43978-4_2204

Name

Greek: onkos = nodule, kerkos = tail.

Synonyms

Nodule worm.

Geographic Distribution

Central Africa, Yemen, local in Central America.

Life Cycle

Figure 1 (page 1045);  Filariidae, Fig. 1. Males 4 cm and females up to 70 cm live for 20 years and more in human skin. Often many females lay close together and form nodules (Figs. 2, 3, 4, and 5, pages 1046, 1047), within which they are fertilized by the small, wandering males. The females produce unsheathed microfilariae (310 × 6–9 μm), which occur all day long in the skin (Fig. 6, page 1047) and are driven with the lymph fluid to the eyes ( Eye Parasites) leading to the so-called River-blindness due to immune reaction after their death. These larvae are taken up by bloodsucking simuliid (  Simulium spp.), where they develop into larvae 3 within 6–8 days. The L3 are transmitted during the next bites. The growing up until maturity needs about 9–14 months. However, symptoms of disease may occur earlier (after 3–4 months). The following symptoms are noted: itching, chronical dermatitis, paper skin, blindness. In South-Central America the disease is called Roble’s disease. Onchoceriasis, Man Eye  Eye Parasites,  Blackflies,  Nematodes.
Onchocerca volvulus, Fig. 1

Diagrammatic representation of the life cycle of Onchocerca volvulus. A,B Hosts: Humans and Simulium. 1 Nodules in skin, 2 section through a skin nodule containing several female worms, 3 Posterior end of microfilariae, 4 Larva 2 in vector, 5 Larva 3 (infectious), 6 Way of entering the skin. A anus, AI anlage of intestine, E epidermis, FE bundle of females, IN intestine, L larva, MF microfilaria, N nucleus, NO nodule

Onchocerca volvulus, Fig. 2

Boy with small nodule (arrow)

Onchocerca volvulus, Fig. 3

LM of a bundle of females after experimental digestion of a nodule

Onchocerca volvulus, Fig. 4

LM of a section through a region with a microfilaria leaving the surroundings of a nodule

Onchocerca volvulus, Fig. 5

LM of a nodule with several cross-sectioned females. AW adult females, BG blood capillary, CL cartilage, MFU microfilariae in female uterus

Onchocerca volvulus, Fig. 6

LM of a Giemsa-stained microfilaria from skin. N nucleus

Disease

 Onchocerciasis, Man, Roble’s Disease,  River Blindness.

Copyright information

© Springer-Verlag Berlin Heidelberg 2016