River classification is important for reporting ecological status and for the general ecological management of river systems by partitioning natural variability. A priori river classification by abiotic variables and validation of classifications obtained
A number of human disease prevalences are supported by host-parasite-environment interactions. One such disease is schistosomiasis. Schistosoma parasites are transmitted between the snail intermediate hosts and mammalian definitive hosts in an aquatic environment. This host-environment link determines the parasite transmission dynamics and is a route through which control of transmission can be achieved. Transmission control methods based on manipulating the host-environment link were reviewed, the limitations of each method were highlighted and conditions in which they may be used in small-scale control programmes in sub-Saharan Africa were suggested. Chemical control may be ideal in poor rural communities, where health education strategies have little impact and where fishing is not an important livelihood strategy, because human contact with contaminated water is necessary for parasite survival. In aquaculture and other water development project areas, biocontrol may yield positive results due to reduced predation on snail predators and competitors as a result of restricted access. Environmental modification may be ideal in man-made systems, where the planning phase includes appropriate engineering works. Control strategies must be based as much on the ecology of host snails as on social aspects of the affected community, and be implemented on a case-by-case basis.
Keywords: biological control, host-parasite-environment interactions, human factors