Monday, June 5, 2023

Climate change could drive more Zika and dengue epidemics and longer transmission seasons

Examining how newly emerging diseases will be impacted by specific future climate change scenarios.

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Rising temperatures through climate change are expected to increase arboviral disease pressure, so understanding the impact of climate change on newly emerging diseases such as Zika is essential to prepare for future outbreaks. However, because disease transmission may be less effective at very high temperatures, it is still being determined whether the risk will uniformly increase in different regions.

Given the nonlinear relationship between temperature and many crucial biological vector traits, mathematical modeling is a useful tool for predicting the impact of temperature on arbovirus risk.

Recent work characterizing these temperature dependencies has highlighted how climate change may impact geographic disease spread. A new study extended this prior work by examining how newly emerging diseases, like Zika, will be affected by specific future climate change scenarios in four diverse regions of Brazil: Manaus, Recife, Rio de Janeiro, and Sao Paulo.

They mainly explored how projections might vary across regions within a country and the likely impact of year-to-year temperature variation. They obtained the historical and projected future temperature data from ISIMIP (The InterSectoral Impact Model Intercomparison Project).

For our historical baseline, they used data from 2015–2019, five years encompassing the Zika outbreak in Brazil. For the forecast, they used 30-year projections, i.e., projected temperature data for the years 2045–2049, giving an estimation of overall changes in risk by the second half of the 2040s compared to the recent past.

Zika and dengue’s temperature profile for R0 peaks at a relatively high temperature, around 30˚C. Prior work has suggested that climate change will increase their transmission potential and geographic extent of transmission.

Scientists noted, “When examining the impact of climate change projections on Brazil, we find general agreement with this expectation but also variability across different climatic regions within the country. This variability across different climate zones is evident in which shows that Manaus is a region on the cusp of experiencing a decrease in arbovirus risk at certain times of the year in certain years, while both Recife and Rio de Janeiro show large increases in risk throughout the year.”

“In places like Recife and Rio de Janeiro, we project the extension of the risk season. In São Paulo, we see that it is likely that future arboviral risk will depend on how the climate changes. These results highlight that transmission is likely to expand into geographic regions with cooler climates. Regions with temperatures that are too cold to sustain year-round transmission will become increasingly vulnerable to newly seeded outbreaks sparking seasonal epidemics.”

“Of the four cities in the analysis, Manaus is the only city to reach this peak temperature, and even in the high emission scenario, the maximum temperature in our projections is only briefly above 35˚C at the beginning of October. Thus, even in regions with warmer tropical rain forest climates like Manaus, our results show that in most regions, climate change is not likely to have a substantial or consistent protective effect on arbovirus transmission.”

Journal Reference:

  1. Van Wyk H, Eisenberg JNS, Brouwer AF (2023) Long-term projections of the impacts of warming temperatures on Zika and dengue risk in four Brazilian cities using a temperature-dependent basic reproduction number. PLoS Negl Trop Dis 17(4): e0010839. DOI: 10.1371/journal.pntd.0010839
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