Climate change could cause the spread of new cholera species

In the 20th century, a devastating cholera pandemic, which began in India in 1899 and spread rapidly to other parts of the world until 1923, killed more than 100 people. There are 800,000 people in India alone. An El Niño event may have played a key role in enabling the rapid transmission of a new strain of the bacteria that causes cholera, according to a recent study.

An El Niño event is a global climate phenomenon that occurs due to unusual warming of ocean surfaces in the eastern Pacific Ocean, which then has cascading effects on ocean temperatures and the strength and speed of ocean currents around the world.

“A possible explanation for such a synchronous and extreme cholera event is climatic anomalies occurring over a large geographic region. Another explanation is the emergence of a new species,” the authors explain in the study published in PLOS neglected tropical diseases. “Several of our results support a role of climate as a major driver of the anomalous cholera episode of 1904-1907, which would have facilitated the establishment of this new species.”

“Climate conditions that favor transmission over certain time periods and several consecutive years can facilitate the emergence of cholera, but also of other pathogens that are borne by water and vectors and therefore closely linked to the environment,” says lead author Xavier. Rodo from Instituto de Salud Global de Barcelona, ​​Spain, and colleagues added.

The team obtained climate data from 1893 to 1939 from multiple sources. They then applied various statistical and computational tools to those records of climatic 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 between 1904 and 1907 were reported at the same time as unusual seasonal temperatures and rainfall patterns that could be linked to an El Niño event. At the same time, during this pandemic, there was the emergence of a new strain of cholera bacteria.

In a press release, Rodó and co-author Mercedes Pascual explain: “Variation in climatic conditions or the evolutionary change of a pathogen can be important drivers of major epidemics and pandemics. But these two factors are typically considered separately in studies trying to explain the emergence of unusually large outbreaks. Here we present indirect evidence that the two may work together to synergistically underlie the establishment and widespread transmission of a new species.”

“The finding of a possible delay between initial detection and actual emergence indicates that the relevance of climate conditions may extend beyond the former. For cholera, the shift in monsoon rainfall distribution over Bangladesh to higher values ​​suggests more frequent conditions for transmission and emergence. ,” the authors further explain in the new study. “The increased capacity to monitor genetic changes of pathogens should be coupled with advances in climate studies of infectious diseases, including climate modeling and forecasting, to provide warnings about potential emergence.”