During the 20th century, a devastating cholera pandemic that started in India in 1899 and rapidly spread to other parts of the world until 1923 killed more than 800,000 people in India alone. According to a recent study, an El Niño event might have played a key role in enabling the rapid transmission of a new strain of the bacterium that causes cholera.
An El Niño event is a global climate phenomenon that occurs due to the unusual warming of ocean surfaces in the eastern Pacific Ocean, which then has cascading impacts on ocean temperatures and the strength and speed of ocean currents across the world.
“One possible explanation for such a synchronous and extreme cholera event is climate anomalies acting over a large geographical region. Another explanation is the emergence of a novel strain,” the authors explained in the study published in PLOS Neglected Tropical Diseases. “Several of our results support a role of climate acting as a major driver of the 1904–07 anomalous cholera episode, which would have facilitated the establishment of the novel strain.”
“Climate conditions that enhance transmission during particular windows of time and several consecutive years can act to facilitate emergence in cholera, but also in other pathogens that are water-borne and vector-borne and therefore, closely connected to the environment,” lead author Xavier Rodo of Instituto de Salud Global de Barcelona, Spain, and colleagues added.
The team obtained climate data from 1893 to 1939 from multiple sources. Then, they applied several statistical and computational tools to those records of climate conditions along with analyzing the number of cholera deaths in different parts of India during the pandemic.
They found that growing patterns of cholera deaths from 1904 to 1907 were reported at the same time as unusual seasonal temperatures and rainfall patterns which could be associated with an El Niño event. Simultaneously, there was an emergence of a new strain of cholera bacterium during this pandemic.
In a press release, Rodó and co-author Mercedes Pascual explained: “Variation in climate conditions or the evolutionary change of a pathogen can be important drivers of major epidemics and pandemics. But these two drivers are typically considered separately in studies seeking to explain the emergence of unusually large outbreaks…here, we present indirect evidence that the two can act together to synergistically underlie the establishment and widespread transmission of a new strain.”
“The finding of a possible delay between initial detection and actual emergence indicates that the relevance of climate conditions can extend beyond the former. For cholera, the shift of the distribution of monsoon rains over Bangladesh towards higher values suggests more frequent conditions for transmission and emergence,” the authors further explained in the new study. “The increased capacity to monitor genetic changes of pathogens should be coupled to advances in climate studies of infectious diseases including climate modeling and prediction, to provide warnings about potential emergence.”
