In a year that broke records for infections denguewith almost 12 million of cases only in the American continent until the month of October and 763.421 So far in 2024 in Argentina, scientists from the universities of Stanford y Harvard identified an increasingly influential factor: the climate change. According to a recent study, presented at the Annual Meeting of the American Society of Tropical Medicine and Hygiene (ASTMH), but not yet published, the highest temperatures represent the 19% of current load of the condition in the world, a figure that could increase up to 200% in certain regions for the 2050.
As the global warming transforms the planet, it also redefines the scope and intensity of vector-borne diseases such as dengue, as it creates optimal conditions for its spread in previously unaffected areas. Faced with this scenario, a Brazilian city, Niteróistood out as a rare exception amid the most severe outbreak of the infection in Brazil in 2024.
The strategic implementation of mosquitoes carrying the Wolbachia bacteriawhich interferes with the transmission of the virus, managed to significantly reduce cases, according to a second study that was presented at the meeting of ASTMH. This innovative method is emerging as a key tool in the fight against a condition that intensifies with temperatures that continue to rise.
The global increase in temperatures expanded the geographical areas where the mosquitoes Aedes aegyptithe main transmitters of dengue, can survive y breed. Warm climates not only favor the expansion of these insects, but also increase their ability to transmit the virus.
As temperatures rise above 20 °C and remain within the optimal range of 28-29 °Cinfected mosquitoes produce a greater amount of viral particleswhich increases the probability of transmission. This dynamic led to a significant increase in cases in already endemic countries such as Brazil, Mexico y Peruand also allowed the emergence of indigenous infections in areas previously considered dengue-free, such as California y Florida in the United States.
The study also warns that the effects of climate change will continue to intensify even with significant reductions in carbon emissions, and will mainly affect regions that are barely within the temperatures required for transmission.
The scientists analyzed data on the incidence of dengue and climate variations in 21 countries from Asia and America. The investigation focused on evaluating whether there was a direct relationship between rising temperatures and infection rates, while also considering additional factors such as rainfall patterns, population density and economic crises.
The results were clear: the highest temperatures within the ideal range not only increase the population of mosquitoes, but also accelerate their life cycle and raise the amount of virus that they can transmit. Regions of Mexico, Bolivia and the north of Brazilwhich historically were at the lower threshold of optimal temperature, now face a increasing risk.
“This shows that climate change has already become a major threat for human health and, in the case of dengue in particular, our data suggest that the impact could be much worse,” the Dr. Erin Mordecaian infectious disease ecologist at Stanford’s Woods Institute for the Environment and lead author of the study.
On the other hand, the study showed that areas that are already at the upper end of the thermal range, such as the about Vietnamthey could experience few additional impacts or even minor decreases in infections, as mosquitoes reach their limit. However, the researchers stressed that 257 million people currently live in areas where the incidence of dengue could double in the next 25 years due to climate change.
This connection between temperature and transmission not only highlights the role of global warming in health, but also highlights the importance of mitigation measures that combine the reduction of greenhouse gas emissions with specific strategies to control the spread.
Releasing mosquitoes infected with Wolbachiaa natural bacteria that prevents the transmission of dengue and other viruses such as Zika and chikungunya, proved to be a revolutionary breakthrough in the fight against the disease, according to another study published at the meeting of ASTMH. This preventative approach does not eliminate the insects, but rather turns them into allies in reducing viral load.
In NiteróiBrazil, where the release of Wolbachia was completed in 2023, cases decreased dramatically, even amid the most severe outbreak on record in the country. Over five years, the average incidence in the city went from 913 to 84 cases per 100,000 inhabitants.
“We had already seen that infections had stagnant practically in Niterói after the implementation of Wolbachia and, while there was a small increase in 2024, the number of cases was still a 90% less than before of the implementation, and nothing similar to what was happening in the rest of Brazil,” he stated Katie AndersPhD, director of impact evaluation at the World Mosquito Program, who led the global effort to combat dengue with mosquitoes infected with the bacteria.
In addition to Brazil, other countries such as Indonesia y Colombia They implemented the strategy with promising results. In these areas, tests confirmed that the bacteria is safe for the environment and human healthin addition to being an effective tool to mitigate the intensity of outbreaks.
The success of the program in Niterói prompted a national effort in Brazil to expand the use of Wolbachia as a standard, rather than experimental, control measure. He Ministry of Health from Brazil and the World Mosquito Program are jointly building a facility dedicated to mass production of mosquitoes infected with the bacteria that will allow releases in several cities simultaneously, with the aim of protecting millions of people.
Despite its potential, the strategy faces logistical and economic challenges. Implementation requires the initial release of a large number of insects containing the pathogen in their system, which requires a advanced infrastructure and a significant financial commitment. Furthermore, the impact of Wolbachia is not immediate: it takes at least two years for the bacteria to spread sufficiently in the local mosquito population and reach its maximum effectiveness.
However, its effect is long-lastingaccording to the results of studies carried out in Australiawhere Wolbachia was introduced in 2011 and is still present in 90% of local mosquitoes more than a decade after initial releases. This long-term effect makes it a sustainable solution for countries affected by dengue.
Despite advances in the control of the condition, there are no specific medicines to treat it, and vaccines available face challenges that limit their widespread adoption. This reinforces the need for preventive measures such as Wolbachia and global strategies to mitigate the impact of climate change in public health.
Although the analysis on the impact of global warming on dengue provides solid evidencethe researchers warn that the study could underestimate the real magnitude of the problem. This is due to the lack of consistent data in endemic areas such as Sub-Saharan Africa and the south asiawhere cases are not uniformly recorded, but where climatic and demographic conditions indicate a high potential for future outbreaks.
Additionally, researchers were unable to accurately project impacts in regions where dengue is just beginning to emerge, such as the southern United States. “But as more and more of the United States approaches that optimal temperature range for dengue, the number of locally acquired infections is likely to increase, although it is too early to say how that will affect the global burden.” Mordecai indicated.
