Malaria and dengue are projected to affect billions more people

An estimated 8.4 billion people could be at risk for malaria and dengue by the end of the century if emissions continue to rise to current levels, according to a new study published in Planetary Health Lancet.

The research team estimates that in the worst case would mean that the population at risk of disease could increase to an additional 4.7 billion people (compared to the period 1970-1999), particularly in the lowlands and urban areas, if temperatures rise by about 3.7 ° C 1 by 2100 compared to pre-industrial levels.

The study was led by the London School of Hygiene & Tropical Medicine (LSHTM) with partners from Umeå University, Sweden; Abdus Salam International Center for Theoretical Physics, Italy; University of Heidelberg, Germany; and the University of Liverpool.

The team used a series of models to measure the potential impact of climate change on the length of the transmission season and the population at risk of two major mosquito-borne diseases, malaria and dengue, in the late 21st century. compared to 100 years earlier. . They made their predictions based on the different levels of greenhouse gas emissions, population density (to represent urbanization) and altitude.

For malaria, the worst-case modeling estimated that a total of 8.4 billion people were at risk in 2078 (i.e., 89.3% of an estimated global population of 9.4 billion) compared to a average of 3.7 billion during the period 1970-1999 (i.e., 75.6% of an estimate world population of 4.9 billion) 2. For dengue, modeling estimated a total of 8.5 billion people at risk in 2080 compared to an average of 3.8 billion in 1970-1999.

It is estimated that the suitability of malaria will gradually increase as a result of a warming climate in most tropical regions, especially mountainous areas of the African region (e.g., Ethiopia, Kenya, and South Africa), the Eastern Mediterranean region (e.g., Somalia, Saudi Arabia, and Yemen), and the Americas (e.g., Peru, Mexico, and Venezuela). The suitability of dengue is expected to increase mainly in the lowland areas of the Western Pacific region (eg Guam, Vanuatu, Palau) and the Eastern Mediterranean region (eg Somalia and Djibouti) and in the highlands. of the Americas (e.g., Guatemala, Venezuela, and Costa Rica).

The research predicts that there will be a northward shift of the malaria epidemic belt in North America, northern Central Europe and northern Asia, and a northward shift of the dengue epidemic belt north of Central Europe and the northern US due to increased suitability.

All scenarios predicted an overall increase in the population at risk of malaria and dengue over the century. However, the impact would be substantially reduced if action were taken to reduce global emissions, according to the modeling.

In the scenario where emissions are further reduced: greenhouse gas emissions decrease in 2020 to zero in 2100 and the global average temperature increases by 1 ° C between 2081 and 2100; an additional 2.35 million people are expected to live in areas suitable for malaria transmission. For dengue in this scenario, modeling suggests that there are an additional 2.41 million people at risk.

The study highlighted that if emission levels continue to rise to current levels, high-altitude tropical areas (more than 1,000 meters above sea level) in areas such as Ethiopia, Angola, South Africa and Madagascar could experience up to an additional 1.6 months climatically suitable for malaria transmission in 2070-2099 compared to the period 1970-1999.

The study predicted that the length of the dengue transmission season could increase by up to four additional months in the lowlands of Southeast Asia, sub-Saharan Africa and the Indian subcontinent.

The first author, Dr. Felipe J Colón-González, assistant professor at LSHTM, said: “Our results highlight why we need to act to reduce emissions to limit climate change.

“This work strongly suggests that reducing greenhouse gas emissions could prevent millions of people from contracting malaria and dengue. The results show that low-emission scenarios significantly reduce the duration of transmission as well as the number Actions to limit the rise in global temperature should continue well below 2 ° C.

“But policymakers and public health officials should be prepared for all scenarios, including those where emissions remain high. This is particularly important in areas that are currently disease-free and where it is likely. that health systems are not prepared for major outbreaks. “

Climate change has raised concerns that mosquito-borne disease transmission is intensifying through increased vector survival and bite rates, increased replication of pathogens within vectors, shorter reproduction rates, and longer transmission seasons.

Malaria and dengue, the world’s major mosquito-borne threats3, are found in more areas, gradually emerging in hitherto unaffected areas and reappearing in places where they had declined for decades. Malaria is shifting to higher altitudes and urbanization is associated with an increasing risk of dengue.

Although the differential effects of climate change with altitude and urbanization have been previously discussed, so far they have not been quantified globally by different levels of altitude and urbanization.

The research team’s methods consisted of identifying risk for each region of the World Health Organization (WHO) 4 using six combinations of emission and socioeconomic scenarios ranging from conservative to business. as always5 and six disease models.

Although worst-case models indicate that some areas may become too hot for some mosquito species, this situation is likely to cause other health effects, such as heat mortality, reduced labor productivity, and production. of food.

In addition, mosquito-borne diseases could become a bigger problem elsewhere, including their expansion northward and into higher, temperate regions, as climatic conditions such as temperature and rainfall allow malaria to thrive and dengue in different parts of the world.

The main author, Dra. Rachel Lowe, associate professor and fellow of the Royal Society, Dorothy Hodgkin Fellow of LSHTM, said: “Various interventions will be needed to adapt to the health effects of a warmer, more urbanized world and prepare for all. the scenarios.

“Our findings underscore the importance of increased surveillance in potential areas to control disease outbreaks, especially in places with no previous experience of dengue or malaria.

“Public health action will be particularly important in areas where transmission is occasional because public health systems may not be prepared to control and prevent these diseases.”

The authors acknowledge limitations in the study, including the fact that they did not take into account the effects of socioeconomic development, the evolution of diseases and vectors, or the development of more effective drugs and vaccines, all of which could lead to differences. important in the amount of simulated risk. Estimates are also constrained by the selection of climate and disease models and the selected combinations of emission and socioeconomic scenarios. In future experiments, researchers could incorporate larger model sets and scenario combinations to provide a richer view of the uncertainty surrounding the estimates.