Above: Saliva collection from Zika-exposed and control Aedes aegypti mosquitoes. Photo by Blanka Tesla.
Zika was once thought of as a problem contained to tropical and sub-tropical parts of the world. Today we know better – with 3.9 billion people in 120 countries around the globe at risk of contracting some type of arboviral disease – Zika and related diseases like dengue and chikungunya are spreading, opening up the threat to more and more of the world’s population as our climate changes.
In a new study recently published in the Proceedings of the Royal Society B, researchers from the University of Georgia, Stanford University, Harvard University, and the University of Florida have found that temperature is a driving factor in the transmission of the Zika virus. The team, led by Dr. Courtney Murdock, an assistant professor of infectious disease and ecology at the University of Georgia College of Veterinary Medicine and Odum School of Ecology, and Blanka Tesla, a graduate student at UGA, measured the effect of temperature on the probability of transmission from an infectious mosquito to a human, how quickly the virus spreads throughout the mosquito’s body, allowing it to get into their saliva and become infectious, and areas in the world most suitable for Zika transmission.
They discovered that temperature had a strong effect on mosquito infection and survival traits, and that the least optimal temperatures for transmission were the highest and the lowest temperatures they tested. Thus, as temperatures edge upwards due to climate change, increasing urbanization, or with time of the year, the environmental suitability for Zika transmission should increase. This would result in an expansion of Zika further north and into longer seasons. In contrast, areas that are already permissive or near the thermal optimum for Zika transmission are predicted to experience a decrease in overall environmental suitability.
They then compared the Zika transmission model to one used to predict dengue. Here they discovered that Zika is transmitted more readily at warmer temperatures than dengue virus, which means that current estimates on the global environmental suitability for Zika transmission using dengue as a surrogate are vastly over-predicting its possible range.
“While there are certainly other factors that need to be examined when it comes to the transmission of Zika, this study established that temperature plays a very important role,” said Courtney Murdock assistant professor of infectious disease and ecology at the UGA College of Veterinary Medicine and Odum School of Ecology. “As climate change continues to evolve worldwide, this shows us that we need to keep a watchful eye on how rising temperatures impact the spread of these types of disease.”
The full article was published in the Proceedings of the Royal Society B on August 15, 2018.