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The idea that climatic cycles such as the El Niño/Southern Oscillation significantly affect infectious disease, raised by Rita R. Colwell (Association Affairs, 20 Dec., p 2025) in the context of cholera outbreaks, is supported by recent findings from veterinary, entomological, and botanical epidemiology (1, 2).
Botanical epidemiologists have found that plant systems have unique advantages for macro-scale, long-term epidemiological studies. Weather and climate are important driving forces affecting plant disease development. For example, the U.S. Department of Agriculture's annual cereal rust survey, a program started in 1917 to monitor rust outbreaks over North America, accumulates time series of disease intensity, yield loss, and races of rust fungi in cereal crops (3). With these data, consistent and significant coherence patterns between El Niño and wheat rust intensity have been found in both the Eastern and Western hemispheres (2).
Studies of El Niño-disease associations and their underlying mechanisms could lead to the development of early warning systems. Colwell advocates the use of satellite surveillance for predicting cholera outbreaks, while others propose using El Niño forecasts for malaria alerts (4). Outbreaks of wheat scab in eastern China can be predicted successfully 4 months in advance by measuring sea surface temperatures in the central Pacific (R2 = 0.86; P < 0.001) (5); the mechanism for this association is thought to be the El Niño-dependent advance of the summer monsoon through East Asia, whereby increased precipitation causes increased infection by the scab pathogen. El Niño-disease studies are important also in the context of climate change research: infectious diseases driven by multiyear climatic cycles are likely to respond to slow, decadal changes in climate as well.