Major climate events have opened up land bridges during prehistory, along which animals and humans traveled to new continents. A new study proposes that major weather events, like El Niño, open up “water bridges” that allow bacteria to do the same.

An international team of researchers has been working with the National Institute of Health (INS) in Peru, looking at the genetic history of pathogens that have sprung up in Latin America over the past few decades. They found odd correlations with pathogens that were already established in Asia.

This could be attributed to people or livestock carrying the pathogen making it across the ocean in boats. But based on the timing, the researchers believe it could be an unknown consequence of El Niño. Their findings are published in Nature Microbiology.

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When looking at disease-causing agents, the researchers were specifically looking at vibrios—bacteria that float around in sea water. Not all of these bacteria are harmful, but about a dozen cause serious illnesses, including cholera and the deep misery that’s the result of eating undercooked shellfish.

A horrible cholera outbreak in 1990 killed 13,000 people in Peru. In 1997 and 2010, there were two major outbreaks of Vibrio parahaemolyticus, the bacteria that contaminates shellfish. These outbreaks also correspond with major El Niño weather phenomenons.

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The bacteria aren’t efficient travelers on their own, but they do associate closely with zooplankton. Zooplankton are champion drifters, particularly if something gives them an opportunity to travel. The researchers believe that major El Niño events give them just such an opportunity. While we’re focused on the weather, an invisible bridge of water could be opening up between continents, letting all kinds of microbial life travel from one shore to the other.

This means that El Niño isn’t just a time when coastal rescue or disaster relief services have to be on guard—it’s a time when national health services need to prepare for foreign pathogens to end up on local shores.

[Nature Microbiology]