This is because the bacteria, which are typically found in salty water, could ‘piggyback’ on zooplankton that travel to Peru and Chile with the warm easterly and southerly Pacific currents associated with El Niño, according to a comment published in Nature Microbiology last month.
Vibrio bacteria cause severe diarrhoea when people eat raw, contaminated molluscs such as oysters, clams and mussels. Such outbreaks have been linked to previous El Niño episodes.
The ongoing El Niño — dubbed El Niño Godzilla because of its intensity — may be the strongest on record. It is developing similarly to an episode in 1977, during which a diarrhoea epidemic broke out in Peru. In that year, Vibrio parahaemolyticus bacteria caused an estimated 10,000 cases of severe gastroenteritis along the South American coastline.
In 1997, another strong El Niño year, the Vibrio parahaemolyticus strain of the bacteria, which had emerged in India, plagued the South American coast.
“The emergence of cases correlated with southward dissemination of El Niño water during the 1997 event,” says Jaime Martinez-Urtaza, a biologist at the University of Bath in the United Kingdom, and a coauthor of the article.
In terms of cholera, South America had been free of the disease for almost a century — until it reemerged in the early 1990s. Within weeks, cholera spread across South and Central America, going on to cause more than a million cases and 10,000 deaths by 1994. Martinez-Urtaza says the cholera outbreak “coincided in both time and space with a significant El Niño event in late 1991 and early 1992”.
Ronnie Gavilán, a researcher at Peru’s National Institute of Health, says there is other evidence for El Niño’s influence on Vibrio bacteria in the Americas. He points out that, during warm El Niño events, Vibrio infections continue to spread in the cold winter months, when they usually only occur in hot summers.
The current El Niño has not yet led to a Vibrio outbreak, but health authorities in Chile and Peru are closely monitoring water quality near the coast.
The delay could be “because the pathogens that may have arrived during the summer season may show up years later”, says Romilio Orellana, a biochemist at the University of Chile.