Onchocerca volvulus
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Onchocerca volvulus |
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| ( Leuckart , 1894) |
Onchocerca volvulus ( gr. Όγκος "barbs" κέρκος "tail"; lat. Volvulus "little balls") is the name of a tropical to the filaria belonging nematode . It is a parasite of humans and the causative agent of river blindness .
distribution
Onchocerca volvulus occurs in large areas of tropical Africa and in central and northern South America. An isolated stove lies in Yemen .
Its distribution area is limited to wet regions along fast flowing rivers.
features
The adult worms are very narrow (thread-like) with a diameter of less than a millimeter. Females can be up to 70 centimeters long, the male reaches a maximum length of 40 millimeters. The microfilariae (larval form) are 220 to 280 µm long.
Life cycle
Like all parasitic filariae, onchocerae have a life cycle with host change . Man is the only ultimate host . In endemic areas, almost 100% of the population is infected. The female black flies ( Simulium damnosum ), which ingests the microfilariae when it bites , serves as the intermediate host . In the mosquito, the larvae develop through moulting to the infectious stage L3, in which they are transmitted to humans when they bite again. They migrate through the connective tissue and occasionally through the eyes for a year or two. Fully grown (adult) worms survive for years encapsulated in subcutaneous nodes ( onchocercomas ). Several filariae are often found in one such knot. The females produce around a thousand microfilariae every day, which migrate through the lymphatic clefts of the connective tissue and are finally washed into the bloodstream. The microfilariae also attack the eye, which is the main damaging effect (blindness).
Black fly at the blood meal
Black fly with Onchocerca filaria emerging from the left antennae
See also
literature
- Fritz H. Kayer et al .: Medical Microbiology , Thieme, Stuttgart (1998)
Web links
- Tropical Diseases Research ( Memento October 15, 2002 in the Internet Archive ) of the World Health Organization
- Scheme of the life cycle (English)
