Volcanic mega-eruptions may trigger major cholera outbreaks

ABSTRACT: Reviewing the results of environmental epidemiology, post-volcanic climatology, and environmental history, we focused exclusively on volcanic eruption-ENSO and ENSO-cholera connections in order to establish a hypothesis that large tropical and Northern Hemisphere volcanic eruptions trigger an environmentally driven cascade process via post-volcanic ENSO anomalies. This cascade process has tended historically to lead to cholera outbreaks in Bengal (i.e. the Ganges-Brahmaputra delta region of modern India and Bangladesh). To test our hypothesis, we set up a dataset from strong tropical and Northern Hemisphere volcanic events that forced the ENSO system, ENSO indices, and historical data for cholera outbreaks. Eight volcanic eruptions (≥3.3 W m^-2) were accompanied within 2 yr by El Niño events over the past 500 yr. For the 19^th-20^th century period, all selected volcanic eruptions were accompanied by major cholera outbreaks in Bengal during the examined post-volcanic years. For the past 500 yr, the likelihood of the occurrence of major post-volcanic cholera outbreaks was 75%.