18 August 2019
A ‘perfect storm’ for the future spread of the Zika virus
Published online 29 January 2019
More frequent, extreme El Niño years could increase the number of mosquito-borne disease epidemics in South America and beyond.
The Zika virus (ZIKV) epidemic of 2015-16 made global headlines as it rapidly spread through the Americas and southeast Asia. One driving force behind the epidemic was a perfect storm of hot and wet weather brought by a strong El Niño.
Now, scientists in Brazil, together with researchers in India and Saudi Arabia, have analysed model predictions of the frequency and intensity of future El Niño years, to verify the likelihood of ZIKV or other mosquito-borne diseases hitting South America hard again1 .
“Recent research published in Nature indicates that, if current trends in global warming continue, extreme El Niño events will double in frequency,” says Vadlamudi Rao of the National Institute for Space Research in Brazil. “We highlighted six potential extreme El Niño years throughout the 2070s to 2090s, and analysed probable air temperatures to determine which areas of South America could be worst hit by ZIKV.”
ZIKV is carried by the Aedes aegypti mosquito, which feeds on human blood. The mosquito’s breeding patterns and survival are strongly dependent on temperature. Its eggs develop best between 27ºC and 40ºC. Rao and his team found that air temperatures across most of South America could easily be within this range, with possible epidemic hotspots including the Amazon forest, Brazil’s São Paulo region, and northern Argentina.
Mosquitoes require pools of still water in which to breed, so rainfall patterns can also contribute to their success. Even in hot, dry conditions, stored water in households can provide breeding grounds.
“Since these diseases are only likely to increase in the future, it is prudent to prepare,” says Rao. “We are now examining global warming predictions across the tropics, so that we can highlight other regions around the world that could be affected.”
“The recent ZIKV outbreak in Latin America was likely due to a myriad of factors,” points out Cyril Caminade, Research Fellow in Epidemiology and Population Health at the University of Liverpool, UK, and author of a 2017 paper2 that first linked the ZIKV outbreak to El Niño. “Latin American populations were very susceptible to ZIKV infection at that time, partly because the population had never been exposed to ZIKV before.”
There are vaccines in development for ZIKV, and researchers are exploring the feasibility of releasing genetically modified sterile mosquitoes into the wild. Also, once a virus has struck a region, human natural immunity increases, reducing the likelihood of epidemics in subsequent years.
- Rao, V.B. et al. Future increase in extreme El Niño events under greenhouse warming increases Zika virus incidence in South America. npj Clim. At. Sci. 2, 4 (2019).
- Caminade, C. et al. Global risk model for vector-borne transmission of Zika virus reveals the role of El Niño 2015. Proc. Natl Acad. Sci. 114, 119-124 (2017).