Freshwater ecology and biodiversity in the tropics:what did we learn from 30 years of onchocerciasis control and the associated biomonitoring of West African rivers?

摘要

To release humans from river blindness,the Onchocerciasis control Programme in West Africa (OCP) was implemented in 1974 and ended in 2002.It has emphasized preservation of biodiversity and inclusion of long-term fireshwater biomonitoring since its inception,a position that is unique among the other international development programmes.The biodiversity of the disease system of river blindness inlcudes the black fly vector complex and the worm parasite.Several species of black fly vectors differ in their behaviour,which causes differences in the disease transmissilon processes.Likewise,different strains of the worm parasite have different pathogenic potentials and are differently transmitted by the same vector species.The complexity of the onchocerciasis disease system was not expected at the beginning of the control programme.it has been progressively discovered,partly as a result of the improvement of molecular biology techniques during the period of OCP.The biological basis for the control of the disease includes the diversity of invertebrate predators of aquatic stages of the vector as well as the sensitivity of these non-target predators to the diversity of insecticides used during OCP.Both the interspecific and intraspecific (i.e.instar) biodiversity,as well as the diversity of insecticides applied during OCP,produced a diversity of effects on the non-target invertebrates,as well as on the potential predation pressure on the vector from the predators among these non-target invertebrates.Finally two biological products,a microfilaricide drug (ivermectin) enabling chemotherapy of humans,and a biological larvicide (Bt H-14) that became available during OCP,contributed considerably to the success of OCP and provide more examples about the role of greater biodiversity in the more effective control of onchocerciasis.The biomonitoring approach designed to evaluate the environmental effects of OCP activities was also the first,longest,and largest scale biomonitoring programme ever implemented in the tropics.We discuss the criteria used to implement the long-term biomonitoring,as well as problems encountered in operational larviciding and how these were solved.Over the long term,biomonitoring faced various unexpected factors or events that made the interpretation of the results more difficult that thought at the beginning.Some of these factors could have been identified at the beginming of OCP but were underestimated,whereas others could not have been predicted.Additional research (beyond the monitoring itself) has resulted in a better understanding of the dynamics and structure of the freshwater fauna in treated as well as untreated rivers.Thus OCP provided an opportunity to improve knowledge about the temporal dynamics and the zonation of riverine fish and invertebrate communities in West Africa.After almost 30 years of monitoring the effects of larviciding in West African rivers it can be concluded that the effect of insecticides on the aquatic fauna was usually low for fish,whereas results for invertebrates indicate changes of taxa composition and community structure even at the family level.However,this impact should not have affected the general functioning of the aquatic system.