A new report finds that the current projected rate of the warming climate in Brazil may increase risk of Zika and dengue fever to significant levels by 2050. A significant level is represented by an increase of between 10 and 20 percent
The research comes from the University of Michigan and it finds that the transmission seasons are expected lengthen by about two months per year. With this comes the increasing potential for seasonal outbreaks, even within the cooler regions of the country.
To gather the data, the researchers assessed climate change across various climates and selected four cities from diverse climatic regions of Brazil. Each city was located approximately at sea level and within the suitable elevation range for an abundance of Aedes Aegypti – the mosquitoes that spread Zika, dengue, yellow fever and other viruses.
The cities were:
- Manaus, a city in the Amazon Rainforest with a tropical rainforest climate.
- Recife, an Atlantic coastal city with a tropical monsoon climate.
- Rio de Janeiro, an Atlantic coastal city with a tropical savanna climate.
- São Paulo, a southern city with a humid subtropical climate.
The researchers obtained historical temperature data for 2015-2019 and projections for 2045-2049. They used a computerised predictive model that accounted for how the mosquito’s biting rates, the eggs they laid, the probability of adult survival and mortality rate, and the incubation period depend on temperature. This enabled an assessment of the impact of multiple temperature-dependent vector characteristics on disease risk.
According to epidemiologist Andrew Brouwer: “We can expect Zika and other arboviruses to become more of a challenge in Brazil and other countries, like Colombia and Venezuela, as climate change contributes to warming temperatures.”
The transmission potential for these types of viral diseases is measured by the basic reproduction number (or R0). For Zika, this means estimating the number of new cases that mosquitoes would cause in a susceptible population after biting a single infected person.
For example, today the average R0 in Manaus is about 2.3. Current projections suggest this will increase to about 2.5 by 2050. This means disease spread can quickly add up across transmission chains and this will cause larger and faster outbreaks.
In terms of increased risk periods, the arbovirus risk season for Rio de Janeiro is set to increase by about 2-3 months by 2045-2049, and the Zika risk seasons in Recife is predicted to increase by roughly two months.
The research appears in PLOS Neglected Tropical Diseases and the journal article is titled “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.”
