It’s been more than 400 years since dengue fever was first reported in the Americas. Now, cases are surging dramatically across the region – especially in parts of South America.
Over 4.5 million new cases were recorded in the Americas last year, but that record has since been smashed: in a recent briefing, Jarbas Barbosa, director of the Pan American Health Organization (PAHO), said cases of dengue in the Americas have tripled in the past year.
“The increase in dengue cases is observed in all countries of Latin America and the Caribbean; however, three countries in the sub-region in the Southern Cone, Brazil in particular, followed by Paraguay and Argentina, are the ones most affected by the epidemic – representing 92 percent of all cases and 87 percent of deaths related to dengue,” said Barbosa.
This year, dengue has been reported in 69 countries, mainly in the Americas – with over 5.5 million cases and more than 2,000 deaths in Brazil alone.
Most people who catch dengue experience mild symptoms, but the disease can be severe, especially for those who have been infected for the second time.
The dengue virus can cause a severe flu-like illness, including high fever, headache, nausea, rash and body aches. Some people also experience painful muscle spasms, which is why dengue used to be called “breakbone fever.”
To understand the current surge in dengue, we first have to understand how its main carrier – the Aedes aegypti mosquito – has evolved.
“There are thousands of species of mosquitoes, and Aedes aegypti has proven to be very adaptable,” says Christovam Barcellos, a researcher at Brazil’s Climate and Health Observatory, Institute of Health Information and Communication, Oswaldo Cruz Foundation (FIOCRUZ).
“They thrive in temperatures of between 22 and 35 degrees Celsius and need clean water – not rivers and lakes, but in a shady space to breed,” he explains.
“In poorer communities, many people store water in wells or tanks or use buckets in their toilets, so this is exactly the water the mosquitoes are looking for.
“So now, we have a social problem, because some areas in Brazil and most of the Global South don’t have a safe, continuous, permanent water supply,” he added.
Barcellos points out that although mosquitoes feed off of plants and flowers, females need one extra ingredient to produce eggs: blood, especially human blood.
So, these mosquitoes need to find people.
Barcellos notes that dengue outbreaks used to be more predictable and seasonal, with peaks or epidemics every five or six years. But cases started to increase in the mid-1980s, particularly in large coastal cities.
“Now people ask, ‘What is happening, and what can happen in the future? When will this epidemic end?’ The truth is it may never end. It’s becoming the new normal,” he warns.
Barcellos says dengue used to be a problem mainly in urban areas, but that’s now changing – partly due to increasingly frequent and intense heatwaves.
“Winters in the Southern Cone region of South America – Brazil, Uruguay, Argentina, Paraguay and Chile – are getting shorter and warmer. They used to be below 20 degrees Celsius. Now they have increased by 1 to 2 degrees, making them more appealing to Aedes aegypti,” he adds.
Barcellos said that deforestation is also a factor in dengue spreading due to the destruction of biodiverse habitats.
“Mosquitoes living in areas of higher biodiversity face competition. They have natural predators like frogs or toads, so an infestation in these biodiverse areas is more controlled,” he says.
Areas that were once free from dengue are now seeing cases spiral out of control. A study conducted by Barcellos’ team found that dengue transmission has expanded towards zones of higher latitude and altitude in recent decades.
The research shows that in Brazil, for example, the disease has been linked to extreme weather events such as droughts and floods, as well as the expansion of economic activity towards the Amazon through the construction of roads and the degradation of pristine forests.
“In isolated villages in the Amazon or the southeast [of Brazil], dengue transmission isn’t common. But now, more roads are being built, connecting villages and towns, and as people start to circulate, mosquitoes soon follow. When they build a new road, it’s very common to find dengue epidemics in new villages,” he says.
Barcellos notes that one side effect of dengue spreading to new areas is that there is often little understanding of the disease and how to treat it.
“People living in rural areas often aren’t familiar with the disease. Health workers often don’t know how to diagnose or treat it, so more people are dying.”
Even though around 99 percent of dengue cases are preventable, that’s only if patients are quickly diagnosed, treated and receive proper follow-up care – which has not been the case in these new areas where dengue has now taken hold.
Brazil has taken a multipronged approach to controlling the outbreaks, including raising public awareness, spraying insecticides in high-risk areas and conducting a mass vaccination drive.
Another strategy is to prevent the mosquitoes from spreading disease by infecting them with natural Wolbachia bacteria.
The World Mosquito Program, which developed the method, said that Wolbachia blocks viruses like dengue, as well as Chikungunya and Zika, from growing in the bodies of Aedes aegypti mosquitoes – reducing their ability to transmit viruses to people.
In Brazil, these mosquitoes are being bred at a lab run by FIOCRUZ and have been tested in five cities so far.
While there are no easy solutions, Barcellos believes there are still important steps we can take to control the current rise in cases and protect future generations from the disease.
“We must try to control climate change now – reduce greenhouse gases and preserve green areas to reduce local temperatures. We need to maintain our biodiversity and improve water and sanitation – people must have safe, clean water in all households.”
But, he admits, “right now, there is no silver bullet for dengue.”
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