Visualizing Environmental Science

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suggests that cholera, which in 2009 caused more than

4000 deaths in Zimbabwe, is a greater problem as tem-

peratures increase due to climate change. The disruption

of natural environments may give disease-causing agents

an o pportunity to thrive. Cutting down forests, building

dams, and e xpanding agriculture may bring humans into

contact with new or previously rare disease-causing agents

by i ncreasing the population and distribution of disease-

carrying organisms such as mosquitoes (Figure 4.5).

injury worldwide is related to human-caused environ-

mental changes. The environmental component of hu-

man health is sometimes direct and obvious, as when

people drink unsanitary water and contract dysentery, a

waterborne disease that causes diarrhea. Diarrhea, which

can be easily treated if resources are available, causes 4

million deaths worldwide each year, mostly in children.

The health effects of many human activities are com-

plex and often indirect. For example, a recent study

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The drainage ditches that will be added to each side of the road will hold standing

water where mosquito larvae thrive.

© Paul Rapson Science Source Images

Photo by Eric Brissaud/Gamma-Rapho via Getty Images

This test indicates the likely presence

of disease-causing agents in water. A

water sample is first passed through a

filtering apparatus. a. A technician drops

a growing medium and a water sample

on a filter-lined petri dish. b. After

incubation, the number of bacterial

colonies is counted. Each colony of

Escherichia coli arose from a single

coliform bacterium in the original

water sample.

a b