Unravelling the impact of El Niño on waterborne diseases in South America Vibrio species are a diverse genus of Gram-negative bacteria found in marine habitats. In addition to playing a critical ecological role in many marine ecosystems, this genus also includes key pathogens of humans. V. cholerae and V. parahaemolyticus, are amongst the most significant human pathogenic bacteria originating from the marine environment. Cholera alone affects an estimated 3-5 million people worldwide; V. parahaemolyticus is the leading cause of seafood borne bacterial gastroenteritis in the world. Infections caused by Vibrio cholerae and V. parahaemolyticus have shown a steady expansion over the last decades associated with the emergence of pandemic clones. The seventh cholera pandemic began in Indonesia in 1961 and was confined to Asia until 1970 when it reached Africa and Europe. After a long time without any new evidence of dissemination, it re-emerged in northern Peru in 1991 causing more than 1,000,000 cases of cholera in just three years. Likewise, V. parahaemolyticus infections were almost confined to Asia until the emergence of cases associated with a single clone in Calcutta in 1996. We report the first incursion of this clone outside Asia in 1997 causing infections along the coast of Peru. The advent of V. cholerae and V. parahaemolyticus infections on the West coast of South America in 1991 and 1997 represented the two only reported evidences of an eastward drift of Asian variants of these pathogens and both processes were concurrent with the arrival of warm equatorial waters displaced by El Niño.   El Niño is a climate pattern that describes the unusual warming of surface waters along the tropical west coast of South America causing a notable impact on the ocean and weather at global scale. El Niño events occur irregularly and are not strictly predictable and one of the most major manifestations is the zonal displacement of the Indo-Pacific Warm Pool, a body of water which holds the warmest oceanic seawaters in the world. This body of water is subjected to strong east migrations to Ecuador in phase with the movement of El Niño waters. In the Pacific coast of South America, the incoming of El Niño equatorial waters to the American coasts originate the incursion of warm waters of lower salinity moving southward along the coast, which has been shown to transport foreign zooplankton populations into Peru and Chile.  As the survival and spread of vibrios in the marine environment under adverse conditions has been linked to the ability of these bacteria to attach to plankton, we hypothesize that zooplankton provide nutrients and protection to enable vibrios to travel across oceans.   We have been working in Peru over the last 10 years isolating and characterizing Vibrio strains obtained from environmental and clinical sources with the aim of identifying new evidence of the link between populations in Asia and the Pacific coast of South America. As result of these investigations, we have identified in environmental sources in Peru the presence of four genetic variants of Vibrio which had been uniquely previously reported in Asia and, strikingly, all of these variants emerged both in time and space with significant El Niño events. According to these observations, the incursion of invasive plankton populations into the coasts of Peru trapped in the El Niño waters may provide a unique source of novel pathogenic variants of Vibrio.  After more than ten years waiting for a new El Niño episode, the active event provides a unique opportunity to test the hypothesis of the existence of an effective trans-Pacific transference of Vibrio populations in phase with the zonal displacement of El Niño waters. All these aspects will address key aspects of the ecology of zooplankton and Vibrio, and specifically the role of zooplankton in driving the global dispersal of Vibrio through major oceanic corridors, which will be particularly useful protection of populations and prevention of future epidemics. The Global Challenges Research Fund (GCRF) supports cutting-edge research to address challenges faced by developing countries. The fund addresses the UN sustainable development goals. It aims to maximise the impact of research and innovation to improve lives and opportunity in the developing world.