Onchocerca originated in Africa and was exported to the Americas by the slave trade, as part of the
Columbian exchange that introduced other old-world diseases such as yellow fever into the New World. The findings of a phylogenetic study in the mid-90s are consistent with an introduction to the New World in this manner. DNA sequences of savannah and rainforest strains in Africa differ, while American strains are identical to savannah strains in western Africa. The microfilarial parasite that causes the disease was first identified in 1874 by an Irish naval surgeon, John O'Neill, who sought to identify the cause of a common skin disease along the west coast of Africa, known as "craw-craw".
Rudolf Leuckart, a German zoologist, later examined specimens of the same filarial worm sent from Africa by a German missionary doctor in 1890 and named the organism
Filaria volvulus. Rodolfo Robles and Rafael Pacheco in Guatemala first mentioned the ocular form of the disease in the Americas in about 1915. They described a tropical worm infection with adult
Onchocerca that included inflammation of the skin, especially the face ('erisipela de la costa'), and eyes. The disease, commonly called the "filarial blinding disease", and later referred to as "Robles disease", was common among coffee plantation workers. Manifestations included subcutaneous nodules, anterior eye lesions, and dermatitis. Robles sent specimens to
Émile Brumpt, a French parasitologist, who named it
O. caecutiens in 1919, indicating the parasite caused blindness (Latin "caecus" meaning blind). The disease was also reported as being common in Mexico. By the early 1920s, it was generally agreed that the filaria in Africa and Central America were morphologically indistinguishable and the same as that described by O'Neill 50 years earlier. Robles hypothesized that the vector of the disease was the day-biting black fly,
Simulium. Scottish physician Donald Blacklock of the
Liverpool School of Tropical Medicine confirmed this mode of transmission in studies in Sierra Leone. Blacklock's experiments included the re-infection of
Simulium flies exposed to portions of the skin of infected subjects on which nodules were present, which led to the elucidation of the life cycle of the Onchocerca parasite. Blacklock and others could find no evidence of eye disease in Africa.
Jean Hissette, a Belgian ophthalmologist, discovered in 1930 that the organism was the cause of a "river blindness" in the Belgian Congo. Some of the patients reported seeing tangled threads or worms in their vision, which were microfilariae moving freely in the aqueous humor of the anterior chamber of the eye. Blacklock and Strong had thought the African worm did not affect the eyes, but Hissette reported that 50% of patients with onchocerciasis near the Sankuru River in the Belgian Congo had eye disease and 20% were blind. Hisette Isolated the microfilariae from an enucleated eye and described the typical chorioretinal scarring, later called the "Hissette-Ridley fundus" after another ophthalmologist,
Harold Ridley, who also made extensive observations on onchocerciasis patients in northwest Ghana, publishing his findings in 1945. Ridley first postulated that the disease was brought by the slave trade. The international scientific community was initially skeptical of Hisette's findings, but they were confirmed by the Harvard African Expedition of 1934, led by
Richard P. Strong, an American tropical medicine physician. ==Society and culture==