By Karen Levy

A new study in Proceedings of the National Academy of Sciences, a highly respected journal, suggest that the current Zika virus outbreak in the Americas may have been caused by a perfect storm of weather conditions, mosquito populations, and climate change.

The scientists’ global models found that the “Godzilla” El Niño event of 2015 provided ideal conditions for Zika emergence in South America.  Their models concluded that the risk of Zika virus emergence in South America in 2015 was the highest it had been since 1950.  The timing of the model predictions coincides with when high numbers of cases of children born with microencephaly, or abnormally small heads, were first observed in Brazil.  Since then Zika has spread throughout the Americas and Caribbean region.

Several things had to happen for Zika to emerge in Brazil in 2015.  First, Zika virus had to be present.  It is suspected to have been introduced to Brazil in 2013.  Second, the right mosquitos were necessary.  Two mosquitos that are known to transmit Zika virus are abundant in Brazil– Aedes aegypti (‘the yellow fever mosquito’) and Aedis albopictus (‘the Asian tiger mosquito’).  Third, ideal  temperature conditions were needed, because temperature can affect mosquito survival, reproduction, and behavior.  The temperature conditions caused by the 2015 El Niño caused mosquitos to increase how often they bite, and to decrease their development time.  Temperatures also led to lower mosquito death rates.Climate change also created conducive conditions for  mosquitos to thrive.

The authors conclude, “The Zika virus outbreak in Latin America has very likely been fueled by the 2015–2016 El Niño climate phenomenon affecting the region.”

Comparison of Zika virus distribution predicted by the model versus reported cases (Source: Caminade et al. 2016).

The findings are important because they suggest that climate played a large role in the outbreak.  The authors suggest that such a large outbreak of the virus occurred only once the climatic conditions were optimal, after introduction of the virus in Brazil two years prior.

The U.S. Centers for Disease Control and Prevention have advised pregnant women against traveling to areas where Zika virus is present.