Vision 2020: 100 years of river blindness research

Background: The early investigators of onchocerciasis from 1874-1930 in Africa made no mention at all of concomitant severe eye disease. Publications of the observations in Central America in 1917/1919 prompted some specialists in tropical medicine to look for eye disease associated with African onchocerciasis. However, there did not seem to be any eye disease leading to blindness. It was not until 1930/1931 that Hissette reported that 20% of patients with onchocerciasis were blind in an onchocerciasis focus on the Sankuru river in the Belgian Congo, and that 50% of the villagers suffered from eye troubles. Two years later, lie found a second focus with the same pathology on the Uele river. Working hypothesis: We wished to establish why African river blindness manifested itself so unusually late and what criteria must be fulfilled for it to be brought under control quickly. The following questions are examined: (1) Had the early tropical doctors overlooked river blindness? (2) Could the still low distribution and density of microfilariae in the body of the affected patients have determined whether or not eye disease is likely to occur? (3) Had the microfilariae mutated into a more aggressive variety? Results: There are indications confirming all three points in the working hypothesis. Before 1930, cases of African onchocerciasis with ocular complications were demonstrably very localized on the U le river. The reason for this is likely to have been that the severity of the disease still varied from focus to focus at that time and/or because the individuals concerned still had a relatively mild microfilarial infection. Conclusion: in principle, onchocerciasis has reverted to the situation before occurrence of ocular complications in consequence of the on-going control measures even though the insect destruction and mass therapy are sometimes incomplete. This appears to be sufficient to prevent blindness even if onchocerciasis is not cured. Only a few of the present-day patients with river blindness will still be left by 2030. By then, the problem of river blindness is likely to have become a thing of the past.