Natural disasters such as earthquakes can have far-reaching effects beyond the damage caused on the day they occur. The 2010 earthquake in Haiti damaged the already limited sanitation systems leading to areas without adequate toilet and washing facilities; perfect for the spread of infection diseases. Sure enough 9 months following the quake there was an outbreak of cholera which quickly spread across the whole country.
Cholera exists in the environment in a non-pathogenic form, which becomes dangerous when it picks up the genes for the cholera toxin. These genes are found within bacteriophages (viruses that infect bacteria) and these bacteriophages can spread the toxin genes through a cholera population, mobilising them to their pathogenic forms. Since 1817 there have been 7 major cholera pandemics, each caused by a different subgroup of the Cholera toxin. However none of these pandemics had ever before reached Haiti.
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