For much of the summer, temperatures had soared from their normal 80-90 degrees Fahrenheit and hovered around 124 degrees. Three-month monsoons led to conditions conducive to breeding malaria, dengue fever, and pneumonic plague. By the time the epidemics ran their course, the three diseases had afflicted thousands of people and killed as many as 4,000. And because climate variability can be forecasted, the potential exists to predict the likelihood of outbreaks of infectious disease. ENSO Disrupts Ecosystem Dynamics Climatic extremes effect animal, plant and human health by affording opportunistic species fresh terrain and generating new bursts of activity.
Droughts encourage locusts and rodents, while floods foster fungi and mosquitoes.
Fluctuations in climate which alter the structure or function of ecosystems can change the population dynamics of opportunistic pests and disease vectors, and of the predatory species which normally check their population growth. Owls, for example, help control rodent populations involved in Lyme disease and Hantaviruses. In the U.S., deforestation in the Pacific Northwest and prolonged drought in the Southwest, both encourage the proliferation of rodents by damaging owl refuges. Rodents are involved in the life-cycle of many groups of diseases around the world. Since the 1960's researchers in southern Asia have observed an association between algal blooms and upsurges of cholera.