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National Institute of Environmental Health Sciences

Your Environment. Your Health.

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Global Disease Outbreaks Enhanced by El Niño

By Janelle Weaver

The exceptionally strong El Niño event of 2015 - 2016 generated excess rainfall and flooding, drought, and temperature extremes that created ecological conditions potentially favoring disease transmission in affected regions worldwide. The findings, published February 13, 2019, in the journal Scientific Reports, suggest that global satellite monitoring of key climate anomalies could identify regions at elevated disease risk and help prevent the spread of diseases.

“The study illuminates that climate variability globally is a significant driving force influencing patterns of disease outbreaks,” said first author Assaf Anyamba, Ph.D., a research scientist with Universities Space Research Association at the National Aeronautics and Space Administration (NASA) Goddard Space Flight Center. “The implication is that we need to pay focused attention to weather and climate patterns, as variations in these patterns result in diseases of global public health significance. In addition, in a highly globalized world of today, it does not take much for these diseases to cross boundaries and continents.”

(B-upper image) December-February 2015/16 global mean SST anomalies during the peak ENSO season. (C- lower) May-July 2016 cumulative rainfall anomalies during the ENSO early phase
(Upper image) December-February 2015/16 global mean SST anomalies during the peak ENSO season. (Lower) October - December 2015 cumulative rainfall anomalies towards the ENSO peak phase.
(Images courtesy Anyamba, A. et al (2019) Global Disease Outbreaks Associated with the 2015–2016 El Niño Event. Scientific Reports, Volume 9, No. 1930)

The El Niño-Southern Oscillation (ENSO) phenomenon has profound impacts on global climate and weather anomaly patterns. These extremes in precipitation and temperature resulting from ENSO events are now known to be background drivers of a range of vector-borne and waterborne diseases, such as chikungunya, dengue, malaria, and plague. This is due to the development of favorable ecological conditions under which arthropod and rodent vectors of human and livestock pathogens emerge in large numbers, thereby increasing disease transmission risk.

Geographic distribution of various disease activity worldwide
Geographic distribution of various disease activity worldwide (between April 2015–March 2016) compiled from various sources.
(Image courtesy Anyamba, A. et al (2019) Global Disease Outbreaks Associated with the 2015–2016 El Niño Event. Scientific Reports, Volume 9, No. 1930)

In the new study, researchers from NASA, the U.S. Department of Agriculture, and the U.S. Department of Defense (DoD) collaborated for the first time to leverage a variety of earth-orbiting satellite data sources and ENSO monitoring and mapping to protect public and veterinary health worldwide. Throughout the 2014 - 2016 period, this interagency group systematically monitored the development of ENSO-induced environmental conditions conducive to elevated disease transmission risk. In particular, the researchers analyzed patterns of some disease outbreaks during the strong 2015 - 2016 El Niño event in relation to climate anomalies derived from satellite measurements.

Disease outbreaks in multiple regions worldwide followed shifts in rainfall, temperature, and vegetation. These shifts favored ecological conditions appropriate for pathogens and their vectors to emerge, propagating clusters of disease activity in these regions. The intensity of disease activity in some regions was approximately 2.5%-28% higher during years with El Niño events than those without. For example, above-normal rainfall was associated with plague and hanta virus in Colorado and New Mexico, as well as cholera in Tanzania. On the other hand, dengue in Brazil and Southeast Asia was associated with above-normal land-surface temperatures and persistence of drought conditions.

“In the future, such regional weather anomalies are projected to increase in frequency and severity under global warming scenarios,” said study author Jean-Paul Chretien, M.D., Ph.D., M.H.S., chief of pandemic warning at DoD. “To address this challenge, we hope that this study will sensitize all public health agencies, both at the global and national level, to partner with weather and climate service agencies and design and set up early-warning systems geared towards disease outbreak control and prevention.”

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