Zika Maps

Zika Virus and Temperature 

The maps and data on this page are based on a study called "Temperature drives Zika virus transmission: evidence from empirical and mathematical models" by Tesla et al. 2018

Tesla and her team created models of Aedes aegypti's suitability to transmit Zika Virus. They conducted laboratory experiments to find out the optimal temperatures that mosquitoes could transmit Zika at. Researchers found that Zika transmission occurs at warmer temperatures than Dengue virus, another Aedes aegypti transmitted disease. This means that the model Tesla and her team created predicts that fewer people are at risk for Zika Virus than previously thought. 

The model that these researchers created was also used to predict Zika suitability as a result of climate change. In the following sections we will walk through some of these findings and visualize them through maps.

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Tesla et al. 2018

What is Zika Virus?

Click through the slides to learn more about Zika Virus.

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Symptoms and Spread

Zika Virus was first discovered in 1947 in Uganda. Most people infected with Zika virus do not develop symptoms, but symptoms may include fever, rash, conjunctivitis or "pink eye", muscle and joint pain. However, Zika virus infection during pregnancy can cause infants to be born with microcephaly and other congenital malformations.

In 2015, Zika Virus became a global public health emergency after spreading rapidly from Brazil to 48 other countries and territories in the Americas. Over 200,000 cases of Zika Virus were confirmed, with more than half from Brazil, and there were 2,618 children born with confirmed congenital syndrome associated with Zika virus infection. These numbers are also likely lower than the real number due to underreporting and asymptomatic cases. 

Finding  #1: Mosquito Temperature Range

Researchers found that Aedes aegypti mosquitoes carrying Zika Virus have an optimal range of temperatures at which they can most successfully transmit Zika Virus. The optimal temperature for Zika transmission was determined to be 29 °C (84.2 °F) with a range of temperatures from 22.7 °C to 34.7 °C (72.86 °F to 94.46 °F). To find this range, researchers fed female mosquitoes a blood meal that had been infected by the Zika Virus. Mosquitoes were than raised in different temperature controlled habitats ranging from 16 °C to 38 °C.

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Figure 1 from Tesla et al. 2018

a) "infected" means the percent of mosquitoes who have zika virus inside them  b) "disseminated" means the percent of mosquitoes with virus that spreads to all parts of their body  c) "infectious" means the percent of mosquitoes with Zika virus detected in their saliva which they can then transmit to humans

The graphs to the left show how temperature affects the ability of mosquitoes to become infected with the Zika Virus, and their ability to spread the virus to humans. The colors indicate the temperatures that the mosquitoes lived at. The height of the bars indicates the percent of mosquitoes within each temperature range that were able to complete the infectivity step indicated by the caption below the graphs.

Ultimately, researchers found that if temperatures become too cold or too hot, the mosquitoes will not be able to transmit Zika Virus to humans. This means that as temperatures continue to rise as a result of climate change, some areas may enter into or exit out of this temperature range. We will explore some of these climate change scenarios in later sections. 

Finding  #2: Populations at Risk

Another finding in this paper is that there is a smaller area and population at risk for Zika Virus than previous models predicted. The unique feature about the Tesla et al. 2018 model is that it was created based on laboratory experiments with Aedes aegypti mosquitoes infected with Zika Virus. Previous models were created based on Aedes aegypti transmission of Dengue Virus. This means that the Tesla et al. 2018 models are more precise than other models. 

Figure 5 from Tesla et al. 2018

Months of transmission suitability in North and South America. a) represents the referenced Dengue model and b) represents Zika models in this study

One such finding of this new model is that Zika prefers warmer temperatures than Dengue. This means that there is a smaller range that Zika will able to be transmitted. 

In fact, due to the more narrow temperature range, Tesla et al. 2018 found that there is a 4.3 million km2 decrease in land suitability for year round transmission when compared to the Dengue virus models. This means that there are fewer people at risk for Zika Virus than other models suggested. 

As a result of these findings, more targeted public health approaches can be used to best serve the most at risk areas. 

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Finding  #3: Efficacy of Reduction Strategies

The maps below use the model that Tesla et al. 2018 created. Here we will explore how the different RCP values and climate models will impact suitability for Zika Virus transmission in North America in 2080. Each slider will represent one of the four models, and compare the RCP values of 2.6 to 8.5.

Hadley Model HadGEM2-ES
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Both maps above are for the year 2080 and use the HadGEM2-ES model. The map on the left has an RCP of 2.6 while the map on the right has an RCP of 8.5. R0 > 0 is greater or equal to 25%

Hadley Model HadGEM2-AO

Both maps above are for the year 2080 and use the HadGEM2-AO model. The map on the left has an RCP of 2.6 while the map on the right has an RCP of 8.5. R0 > 0 is greater or equal to 25%

Beijing Climate Center Climate System Model
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Both maps above are for the year 2080 and use the Beijing Climate Center Climate System model (BCC-CSM1.1). The map on the left has an RCP of 2.6 while the map on the right has an RCP of 8.5. R0 > 0 is greater or equal to 25%

National Center for Atmospheric Research’s Community Climate System Model

Both maps above are for the year 2080 and use the National Center for Atmospheric Research’s Community Climate System model (CCSM4). The map on the left has an RCP of 2.6 while the map on the right has an RCP of 8.5. R0 > 0 is greater or equal to 25%

Analysis:

Notice how all 4 models are in agreement that more severe temperature increases, as modeled by RCP 8.5, will lead to increased Zika transmission suitability in the northern United States and Canada, and southern tip of South America. Interestingly, the HadGEM2-ES model is the only one to predict substantially less suitability for transmission in much of Brazil and the surrounding countries.  Therefore, making accurate public health predictions depends on which model researchers choose to analyze. More standardization is needed in this area to make more generalizable and accurate results. 

Finding  #4: Comparing 2050 to 2080

The maps below use the model that Tesla et al. 2018 created. Here we will explore the differences in Zika transmission range for the years 2050 and 2080 through the 4 climate models and RCP levels. Each slider box will represent the year 2050 on the left and 2080 on the right. Try to make visual comparisons between these 32 maps to determine the impact that climate change will have on Zika Virus transmission risk. 

RCP 2.6
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RCP 4.5
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RCP 6.0
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RCP 8.5
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Hadley Model HadGEM2-ES
Hadley Model HadGEM2-AO
Beijing Climate Center Climate System Model
National Center for Atmospheric Research’s Community Climate System Model

Both maps have an RCP of 2.6 and use the HadGEM2-ES model. The left map is for the year 2050 and the right map is 2080.  R0 > 0 is greater or equal to 25%

Both maps have an RCP of 2.6 and use the HadGEM2-AO model. The left map is for the year 2050 and the right map is 2080.  R0 > 0 is greater or equal to 25%

Both maps have an RCP of 2.6 and use the Beijing Climate Center Climate System model. The left map is for the year 2050 and the right map is 2080.  R0 > 0 is greater or equal to 25%

Both maps have an RCP of 2.6 and use the National Center for Atmospheric Research’s Community Climate System Model. The left map is for the year 2050 and the right map is 2080.  R0 > 0 is greater or equal to 25%

Both maps have an RCP of 4.5 and use the HadGEM2-ES model. The left map is for the year 2050 and the right map is 2080.  R0 > 0 is greater or equal to 25%

Both maps have an RCP of 4.5 and use the HadGEM2-AO model. The left map is for the year 2050 and the right map is 2080.  R0 > 0 is greater or equal to 25%

Both maps have an RCP of 4.5 and use the Beijing Climate Center Climate System model. The left map is for the year 2050 and the right map is 2080.  R0 > 0 is greater or equal to 25%

Both maps have an RCP of 4.5 and use the National Center for Atmospheric Research’s Community Climate System Model. The left map is for the year 2050 and the right map is 2080.  R0 > 0 is greater or equal to 25%

Both maps have an RCP of 6.0 and use the HadGEM2-ES model. The left map is for the year 2050 and the right map is 2080.  R0 > 0 is greater or equal to 25%

Both maps have an RCP of 6.0 and use the HadGEM2-AO model. The left map is for the year 2050 and the right map is 2080.  R0 > 0 is greater or equal to 25%

Both maps have an RCP of 6.0 and use the Beijing Climate Center Climate System model. The left map is for the year 2050 and the right map is 2080.  R0 > 0 is greater or equal to 25%

Both maps have an RCP of 6.0 and use the National Center for Atmospheric Research’s Community Climate System Model. The left map is for the year 2050 and the right map is 2080.  R0 > 0 is greater or equal to 25%

Both maps have an RCP of 8.5 and use the HadGEM2-ES model. The left map is for the year 2050 and the right map is 2080.  R0 > 0 is greater or equal to 25%

Both maps have an RCP of 8.5 and use the HadGEM2-AO model. The left map is for the year 2050 and the right map is 2080.  R0 > 0 is greater or equal to 25%

Both maps have an RCP of 8.5 and use the Beijing Climate Center Climate System model. The left map is for the year 2050 and the right map is 2080.  R0 > 0 is greater or equal to 25%

Both maps have an RCP of 8.5 and use the National Center for Atmospheric Research’s Community Climate System Model. The left map is for the year 2050 and the right map is 2080.  R0 > 0 is greater or equal to 25%

Analysis:

Notice how, in general, the 2080 years have more suitability for Zika transmission than the 2050 years. This is likely due to a projected increase in temperature as a result of increasing greenhouse gas emissions. Also notice how RCP 8.5 has more suitable areas than other RCPs. This shows how, as a result of increasing temperatures, more areas will enter the optimal temperature range for the Aedes aegypti mosquito. This means that more people will be at risk for Zika Virus.

 

Better climate change reduction efforts need to be put into place to reverse the warming trend. Navigate back to the Climate Models page to learn more about steps to take to achieve a more favorable RCP path.

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