Climate change and the increase in dengue cases in the region

Coauthors Paulo L. Ortiz Bultó and Madelaine Rivera Sánchez

In the first half of 2023, over 3 million cases of dengue fever have been reported in the Americas, resulting in the deaths of 1302 people. The number of infections exceeds the 2.8 million cases recorded in the same period in 2022 and this increase could be associated, in large part, with the effects of climate change, which have a strong influence, either directly or indirectly, on the spread of the mosquito.

The increase in extreme phenomena such as droughts and floods, which are becoming more frequent and severe, and the loss of biodiversity, which accelerates changes in natural habitats, as well as leading to a rise in forest fires, accentuate the risk of an expansion of epidemics in the region.

We sometimes tend to underestimate the effect of climate change and ignore the fact that it is the most serious environmental problem facing humanity. In fact, if we do not take measures to adapt to and mitigate the effects of climate change, we could run the risk in the not-too-distant future of the extinction of the human species.

It should be remembered that dengue generates both asymptomatic and symptomatic infections that can be slight or severe and can lead to death on many occasions. This occurs mainly among vulnerable groups such as children, the elderly, and people with depressed immune systems, especially in areas with inadequate hygienic and sanitary conditions and low socioeconomic status.

Mosquito adaptation to new conditions

Climate variability as a primary expression of climate change conditions increases mosquito populations and the emergence of viruses such as dengue, by reinforcing their power of mutability and adaptation to new conditions. The main mosquito that transmits dengue is the Aedes aegypti, which breeds in urban environments and whose evolutionary cycle depends on temperature, humidity, cloud cover, rainfall, and radiation, among other climatic variables. This includes winds, which influence the mosquito’s flight and dispersal, as well as the rate of bites.

The influence of climate change disrupts the general circulation of the atmosphere, causing imbalances in the ocean-atmosphere coupling. This situation is conducive to the ENSO event, better known as El Niño, occurring under different conditions to previous ones, with significant variations in the climate expected by the end of 2023 and the beginning of 2024.

In short, the increased presence of low atmospheric pressure centers will exacerbate the variables aforementioned and, when combined, will favor the rapid evolution of the mosquito, shortening its cycle to reach adulthood in a few days. This leads to a considerable increment in adult populations, which could generate an increase in mosquito-borne diseases in our region, some of which have already begun to be manifested. 

The Caribbean and Central America, which have tropical climates, and South America with subtropical climates, present the most unfavorable scenario. In fact, dengue outbreaks have been reported that significantly exceed the average number of cases in the past 5 years. In the first half of 2023, Brazil, Peru, and Bolivia are leading the way in terms of dengue cases, although all countries in the region are reporting significant numbers of cases and even with a rapid geographic expansion to areas where there was no risk of transmission before.

Dengue monitoring in the face of climate change

In Cuba, where dengue has been kept under control without ceasing to be a problem, the Early Warning System (EWS) for dengue was implemented nationwide in 2002. The monitoring of climatic conditions based on bioclimatic forecasts contributes to timely actions to strengthen prevention programs and safeguard the population. Actions were also carried out to reinforce mosquito control and surveillance, valuable information that contributed to improving prediction models and strengthening the warning system.

These advances have been implemented in countries such as Paraguay, Bolivia, Costa Rica, El Salvador, Honduras, the Dominican Republic, and Panama, considering their diverse geographical, climatic, socio-environmental, and epidemiological characteristics, which allowed intervention measures to be taken sufficiently in advance. These measures contributed to minimizing the impact on the health of the population while the period of implementation of the predictive bioclimatic models was sustained.

Currently, the implementation of early warning systems favors the reduction of the number of deaths during El Niño and other extreme events associated with climate change. Another benefit of EWS is the proactive response to the problems and needs posed by the dengue situation in the region. There is an urgent need to intensify the response capacity of the population and health services with sufficient time in advance to take measures to reduce the risk of becoming ill from dengue.

To this end, a pilot project is being developed with the support of the Inter-American Institute for Global Change Research (IAI) to implement a climate-based dengue alert system at the subnational level.

Paulo Lázaro Ortiz Bultó is a researcher at the Institute of Meteorology. Focal Point for the integration of health services, IV-Region-WMO for Cuba. Ph.D. in Economic Sciences and advisor in the region on spatial models for the prediction of climate-sensitive infectious diseases.

Madelaine Rivera Sánchez is the Director of the National Directorate of Surveillance and Antivectorial Control (DNVLA) of the Ministry of Public Health of Cuba. Doctor in Veterinary Medicine and Master in Infectious Diseases.

*Translated by Janaína Ruviaro da Silva from the original in Spanish.

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