Onchocerca volvulis infection transmitted to man by the black gnats of the genus Simulium. Black flies breed along waterways and affected individuals usually live or work within a few kilometers of these sites. The disease characteristically includes dermatologic, lymphatic, ophthalmologic, and systemic manifestations. Two forms of infection are recognized: the benign type, produced by adult worms, involves the junctions of the lymphatic vessels in the subcutaneous tissue, with incapsulation of the worms; and the severe type, in which microfilaria, after being discharged by adult females into the fibrous tissue, circulates through the subcutaneous lymphatic system, often invading the eyes. The disease is a major cause of blindness.
Onchocerciasis is found mainly in Africa and in parts of South America and the Arabian Peninsula, where it was probably introduced from Africa through the slave trade. Official recognition and documentation of the disease only occurred when Western explorers entered these regions. In America the disease is endemic in specific ares of Mexico, Guatemala, Colombia, and Brazil.
The most important signs of the disease include blindness, and scaly, itchy, nodular skin, known as kru kru or craw craw in West Africa. Animal reservoirs of O volvulus have not been found.
In 1875 the microfilariae of O. volvulus were first observed by the Irish naval surgeon John O'Neill (1848-1913) when examining skin snips from patients suffering from craw craw in Ghana.
In 1890 the adult worms were discovered and identified by Patrick Manson (1844-1922), Scottish parasitologist and pioneer of tropical medicine.
In 1891 the morphology of the adult worms was described and reported at a meeting by German zoologist Karl Georg Friedrich Rudolph Leuckart (1823-1898), using samples collected by missionaries from Ghana.
In 1904 the French physician and parasitologist Emile Brumpt (1877-1951) recognizes that the infection occurs most commonly along river banks, and that the microfilariae in the skin come from the deeper cutaneous nodules where adult filariae reside. He also finds that there are no microfilariae in the blood.
In 1915 Rodolfo Robles in Guatemala sheds light on the life cycle and transmission of the parasite. Using case studies of coffee plantation workers in Guatemala, Robles hypothesizes that the vector of the disease is a day-biting insect, and more specifically two anthrophilic species of Simulium flies found in the endemic areas. Robles, however, did not conduct scientific research to verify his hypothesis.
1917 Robles publishes findings on a “new disease” from Guatemala associated with subcutaneous nodules, anterior ocular lesions, dermatitis, and microfilariae.
In 1925, in Sierra Leone, Donald Blacklock (1879-1953) discovered the black fly, Semulium, as the transmission vector of Onchocerca volvulus.
- H. Figueroa Marroquín and C. García Guillioli:
[Present status of Robles' disease in Guatemala] [Article in Spanish]
Salud pública de Mexico, May/June 1971, 13 (3): 399-404.
- Takeshi Suzuki:
A guidebook for Guatemalan onchocerciasis (Robles disease): With special reference to vector control.
Guatemala-Japan Cooperative Project on Onchocerciasis Research and Control, 1983.
- Isao Tada:
Origin of Robles' disease.
Revista de la Asociación Guatemalteca de Parasitología y Medicina Tropical, October 1989, 4 (1): 20-22.
- Christine S. Ament, Lucy H. Young:
Ocular Manifestations of Helminthic Infections: Onchocersiasis, Cysticercosis, Toxocariasis, and Diffuse Unilateral Subacute Neuroretinitis.
International Ophthalmology Clinics, May 2006, 46 (2): 1-10.
- Emedicine from Web MD. Author: Jason F. Okilicz, MD, Assistant Professor of Medicine, Uniformed Services University of the Health Sciences; Fellow, Department of Infectious Disease, Wilford Hall United States Air Force Medical Center
Coauthors: Dirk M. Elston, MD, and Robert A Schwartz, MD.