Ecological disturbances exert an influence on the emergence and proliferation of malaria
and zoonotic parasitic diseases, including, Leishmaniasis, cryptosporidiosis, giardiasis,
trypanosomiasis, schistosomiasis, filariasis, onchocerciasis, and loiasis. Each environmental
change, whether occurring as a natural phenomenon or through human intervention, changes
the ecological balance and context within which disease hosts or vectors and parasites
breed, develop, and transmit disease. Each species occupies a particular ecological
niche and vector species sub-populations are distinct behaviourally and genetically
as they adapt to man-made environments. Most zoonotic parasites display three distinct
life cycles: sylvatic, zoonotic, and anthroponotic. In adapting to changed environmental
conditions, including reduced non-human population and increased human population,
some vectors display conversion from a primarily zoophyllic to primarily anthrophyllic
orientation. Deforestation and ensuing changes in landuse, human settlement, commercial
development, road construction, water control systems (dams, canals, irrigation systems,
reservoirs), and climate, singly, and in combination have been accompanied by global
increases in morbidity and mortality from emergent parasitic disease. The replacement
of forests with crop farming, ranching, and raising small animals can create supportive
habitats for parasites and their host vectors. When the land use of deforested areas
changes, the pattern of human settlement is altered and habitat fragmentation may
provide opportunities for exchange and transmission of parasites to the heretofore
uninfected humans. Construction of water control projects can lead to shifts in such
vector populations as snails and mosquitoes and their parasites. Construction of roads
in previously inaccessible forested areas can lead to erosion, and stagnant ponds
by blocking the flow of streams when the water rises during the rainy season. The
combined effects of environmentally detrimental changes in local land use and alterations
in global climate disrupt the natural ecosystem and can increase the risk of transmission
of parasitic diseases to the human population.