Some Pathogens Benefit
Lots of activities cause forest loss: logging, clearing land for agriculture, road and railroad construction, mining, firewood collection, building dams and irrigation systems, and making room for human settlement. Each one can affect the natural incidence and interaction of disease vectors and hosts, altering disease patterns and behavior.
Many of these activities leave small pools of stagnant water in their wake (in places like logged tree stumps, mining pits, potholes, and village sewers), creating ideal breeding conditions for many disease-carrying mosquito species. Activities like dam building and watershed clearance have even greater impact on water flow and quality, with subsequent flooding and run-off increasing the transmission of water-borne disease.
Forest disturbance can displace predators or hosts of vectors, causing them to switch to human blood as an alternative source of food. Pathogens may also jump directly to new human host when humans venture into newly accessible areas. Disease vectors may benefit in other ways from habitat change, as in Tanzania, where deforestation created sunny breeding sites and warmer temperatures that perfectly suited a particular malaria-carrying mosquito, Anopheles gambiae.
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