How dengue, a deadly disease transmitted by mosquitoes, could spread in a warming world

According to a new study, climate change is expected to increase the spread of dengue, common in warmer climates of the world, such as Brazil and India.

Every year in the world, there are 100 million cases of dengue infections severe enough to cause symptoms, including fever, debilitating joint pain and internal bleeding. An estimated 10 000 deaths from dengue fever – also known as bone fever – are transmitted by Aedes mosquitoes, which also transmit Zika virus and chikungunya.

The study, published Monday in the journal Nature Microbiology, revealed the possibility of a significant expansion of dengue in the southeastern United States, in the coastal areas of China and Japan, as well as in the regions. Australia.

Oliver Brady, an assistant professor at the London School of Hygiene & Tropical Medicine and co-author of the paper, said the research predicts that more people in the United States would be at risk in the next few years. years.

Globally, the study estimated that more than two billion additional people could be at risk of dengue in 2080 compared to 2015 in the context of a warming scenario roughly representing the current trajectory emissions from the planet. This increase is largely a result of population growth in areas already at high risk of contracting the disease, as well as the extension of the range of dengue fever.

To estimate the future spread of the disease, Dr. Brady and his colleagues took data on mosquito behavior and projections on urbanization (a type of Aedes mosquito that spreads the disease is particularly prevalent in cities) and combined them with three different climate scenarios that could happen in 2020, 2050 and 2080. In all three scenarios, the spread of dengue fever has increased.

But how warm the world is is having a significant impact on the spread of the disease.

The research, Dr. Brady added, "suggests that if we better control emissions, we could stop or at least limit this type of spread."

Warming temperatures help to expand the reach of dengue fever because, in part, as it warms up, mosquitoes can thrive in other places where they could not before. Warming temperatures also shorten the time it takes for an adult to become a biting adult and speeds up the time between the time a mosquito contracts a disease and can pass it on. The study's predictions were lower in some regions, particularly in Europe, than previous studies. These studies estimated widespread transmission of the disease on the continent, while Dr. Brady and his colleagues felt that its spread in the region would be limited to parts of the Iberian Peninsula and the Mediterranean.

Aedes aegypti is particularly worrying because, while other species of mosquitoes will sting at will, Aedes aegypti prefers to sting humans.

Much of the southeastern United States was inhabited by mosquito-borne diseases. Malaria was a threat until the mid-twentieth century, when a campaign of eradication of mosquitoes eliminated it. But this campaign largely relied on the liberal application of DDT insecticide, which has had many negative effects on the environment.

In 2018, the Florida Department of Health in Miami-Dade County announced at least one case of locally acquired dengue fever.

This study has limitations, warned Andrew Comrie, a professor in the Department of Geography and Development at the University of Arizona. The paper is a sophisticated use of ecological niche modeling, said Dr. Comrie by e-mail, but "does not address the inter-species competition, predation, or potential adaptation of evolution."

Although there is a vaccine against dengue, it is ineffective for most people. The treatment of the disease is to ensure that the patient receives enough fluids, which can be difficult because of severe nausea and vomiting.

"For a healthy individual, dengue fever is a terrible experience that you will never forget," said Josh Idjadi, associate professor at Eastern Connecticut University, who contracted dengue fever in French Polynesia. "For infants, the elderly and the infirm, they are the ones at greatest risk."