Exceptionally hot and dry winter in northeast Brazil may be linked to outbreak of the zika virus

The World Health Organization this week responded to the serious outbreak of the zika virus, which is transmitted by the Aedes mosquito, by declaring a state of emergency. The outbreak has recently been associated with heavy rains in parts of Latin and Central America as a result of El Niño. However, the new and provisional findings of the study, undertaken by Dr. Paz from the Department of Geography and Environmental Studies at the University of Haifa, together with Professor Jan Semenza of the Stockholm-based European Center for Disease Prevention and Control, suggest El Niño was actually involved in a completely different direction. The relevant factor is not the heavy rain -- which actually fell in areas far removed from the outbreak -- but the wave of exceptionally hot and dry weather experienced over recent months in northeast Brazil, the area where the Zika virus erupted.

According to the findings, based on data from the US agency the National Oceanic and Atmospheric Administration (NOAA), the latter half of 2015 -- the winter and spring season in the southern hemisphere -- saw the highest temperatures since records began, combined with severe drought. The Zika outbreak appeared in these areas over the weeks that followed. Accordingly to Dr. Paz, the exceptional heat and drought were caused by a combination of two factors: Firstly, El Niño, a phenomenon that includes a substantial rise in water temperatures in the Pacific Ocean off Latin America. This phenomenon is known to cause drought in northeast Brazil, and in recent months the El Niño phenomenon has been particularly strong. The second factor is the patterns of global climate change and warming that have affected the entire planet over recent decades.

Dr. Paz adds that it is known that high temperatures (up to a certain limit) encourage an upsurge in the growth rates of the Aedes mosquito, which carries the zika virus. These mosquitoes also require water, and as noted the past six months were not only unusually hot, but also extremely dry. However, previous studies in the area have shown that during periods of drought, local residents store water in containers, thereby creating a convenient habitat for the mosquitoes. Accordingly, the combination of the extreme weather conditions and local residents' response to these conditions created the ideal conditions for the proliferation of the mosquito population.

As noted, this is a preliminary study. The researchers are currently expanding the study in order to gain further insight into the precise nature of the linkage between climatic conditions and the outbreak of the disease. "In light of the health risk, and the fact that the Aedes mosquitoes also carry other viruses, such as dengue fever and chikungunya, it is important to address the impacts of climate which we have found when analyzing the causes of the current outbreak," Dr. Paz concluded.