Tambora and Cholera

The floods, droughts, starvation and disease in the three years following the eruption of Tambora in 1815 stem from the volcano’s effects on weather systems

Tambora’s huge explosive eruption not only led to the 'Year without Summer' but also had a little known effect on the disease ecology of the Bay of Bengal. The enormous cloud of sulfate gases ejected into the atmosphere by Tambora slowed the development of the Indian monsoon, the world’s largest weather system, for the following two years. Severe drought was the result.
Drought brought on by the eruption devastated crop yields across the Indian sub-continent, but more disastrously gave rise to a new and deadly strain of cholera. Cholera had always been endemic to Bengal, but the bizarre weather of 1816-17 triggered by Tambora’s eruption – first drought, then late, unseasonal flooding – altered the microbial ecology of the Bay of Bengal[1].

The cholera bacterium, which has an unusually adaptive genetic structure highly sensitive to changes in its aquatic environment, mutated into a new strain.This met with no resistance among the local population, and it spread across Asia and eventually around the globe. In 1817, cholera began spreading outside the Ganges delta. By September 1817, the disease had reached Calcutta on the Bay of Bengal and quickly spread to the rest of the subcontinent. By 1818 the disease broke out in Bombay, on the west coast. By century’s end, the death toll from Bengal cholera epidemic stood in the tens of millions.
Cholera is an infection of the small intestine by some strains of the bacterium Vibrio cholerae. So virulent is the bacterium that it can kill within hours. Even today, it is estimated that there are 1.4 to 4.3 million cases and 28,000 to 142,000 deaths worldwide due to cholera every year[2].

[1] Boucher et al: The out-of-the-delta hypothesis: Dense human populations in low-lying river deltas served as agents for the evolution of a deadly pathogen in Frontiers in Microbiology - 2015
[2] Lopez et al: The global burden of cholera in Bulletin World Health Organization - 2012

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