By Prof. Adelani Ogunrinade, Contributor
WHAT ARE the legacies of the transatlantic slave trade apart from music, culture and the spirit of Africa? The transatlantic trade also brought with it ancestral legacies such as the hereditary sickle cell anaemia and the infectious disease, river blindness.
What is river blindness and what is its linkage with Africa? Human onchocerciasis or 'river blindness' as it is more commonly known is a disease which takes its name from its occurrence around the great rivers of Africa the Congo, Volta, Niger and Benue and their tributaries expanding across most of Africa South of the Sahara. However, it was not the waters of the rivers which are to blame for bringing river blindness. River blindness is transmitted by black flies known as Simulium. The black fly or Simulium breeds in the rapids and falls in the river, depositing their eggs and larvae on rocks, crabs and vegetation in the river.
When the larvae and pupae mature and become fully-grown flies, it is the painful bite of the flies which transmit the small filarial worm known as Onchocerca volvulus from farmer to fishermen and to communities living around the flood plains of the rivers thus making the disease a perennial, occupational hazard of all who use the freshwater of the great rivers.
River blindness occurs in 22 countries of Africa and six countries of Central and South America - Mexico, Gautemala, Ecuador, Colombia, Brazil and Venezuela; affecting about 20 million people world-wide and causing a disease which in the skin form is know as'craw-craw' and a severe itch; the eye form of the disease results in blindness in about 120,000 people annually.
The black fly (Simulium) occurs where there is a rapid river flowing with some force. The fly is a painful biter thus causing great harm to deers and horses in rural parts of the United States much as it makes life uncomfortable to man around the great rivers of Africa. When the fly bites an individual who harbours the disease, it picks up little worms known as microfilaria (plural microfilariae) and they develop within the fly in about 10 days to form immature third-stage worm which are capable of developing further to adult worms in another man bitten by the infected fly. Very little is known about the development of the immature third stage larva in man but experimental infections in chimpanzees suggest that it takes
11-25 months before adult worms are formed.
In man, adult worms are typically found coiled in nodules below the skin and are typically found as small swellings which vary in size from pea-size to relatively large nodules - the size of a fist of a three-month old baby. These nodules occur usually around the bony prominences in the waist, rib or on arms, legs and other exposed parts of the body. In children, head nodules tend to be common and are regarded as a bad sign because of its nearness to the eye.
If the nodules are incised, they usually contain whitish threadlike coils of female worms which are longer and bigger than the male worms. It is the male and female worms that produce the smaller microfilaria which are picked up by flies in the skin and which crawl all over the skin of an affected individual causing the disease in the skin and in the eye when they invade the eye.
The daily amount of microfilariae released by a single worm is about 1,000 and the average microfilaria wandering around in the skin of a single person has been calculated to be about 12 million per person.
Generally, there are two clinical forms of the disease the forest form which is characterised more by severe, skin depigmentation across the shins known as leopard skin and a loss of elasticity of the skin. On the other hand, the 'savanna ' form is characterised by more manifestations in the eye resulting in blindness. It is not clear whether the two strains of the parasite cause differences because they are two variants or because the savanna is drier than the forest and so more microfilariae are able to accumulate in the eye in the savanna region.
What is the relationship of river blindness to the slave trade ? The fact that onchocerciasis occurs in South America and Africa may provide the clue to the slavery affinity link. However, the prominent researcher Duke has suggested that the two parasite and their vectors are distinct evolutionary strains which may have occurred when the two continents drifted apart millions of years ago. On the other hand, Zimmerman and other scientists using the DNA probe have suggested a link between the African savanna form and the South American strain.
If the latter were so, it wiould mean that majority of the ancestral slaves originated from the savanna and probably brought the disease with them to South America. What happened to the forest strain of the parasite which the forest-dwelling Yoruba and the Ashanti may have brought along to Central and South America and the Caribbean? Regardless of its origins, onchocerciasis represents a major disease which the sustained effort of the World Health Organisation and many African and Latin American countries is trying to eradicate using the drug Mectizan and vector control.
- Prof. Adelani Ogunrinade, Director, Research and Graduate Studies, University of Technology.
