Global Courant
Peru is facing the worst dengue outbreak in its recorded history, with more than 140,000 registered cases so far this year, and more than 200 people are said to have died from complications related to infections.
Dengue is prevalent throughout Peru, especially at lower elevations, though cases tend to decrease as the weather gets drier.
But not this year.
The rainy weather that allows mosquito populations to reproduce — in pools, puddles and standing water — hasn’t stopped, thanks in part to El Niño — the natural, recurring phenomenon that brings warm conditions to the eastern Pacific Ocean and disrupts weather patterns around the world.
Here’s what you need to know about dengue and why weather conditions, exacerbated by El Niño and other factors, could lead to even more infections in Peru and elsewhere.
What is Dengue?
Dengue is a virus transmitted by Aedes mosquitoes, the same species responsible for transmitting other diseases, including yellow fever, Zika and chikungunya.
While those mosquitoes are gift on every continent except Antarctica, they are most common in tropical and subtropical climates.
A male, apex and female Aedes aegypti mosquito, which can carry viruses including dengue, chikungunya and Zika, is seen through a microscope at the Oswaldo Cruz Foundation lab in Rio de Janeiro, on August 14, 2019 (Mauro Pimentel/ AFP/Getty Images)
People who contract the virus may not always show symptoms, but those who do can experience high fever, headache, body aches, nausea and/or rash.
There is no medical treatment, but most people “get over it with a little misery,” said infectious disease specialist and microbiologist Dr. Michael Libman, the director of the Center for Tropical Medicine at McGill University in Montreal.
However, some infections can get serious resulting in shock, shortness of breath, severe bleeding, organ damage and death.
Children are especially at risk in severe cases, when dengue can cause hemorrhagic fevers that can be “quite deadly,” said Dr. David Fisman, a professor of epidemiology at the University of Toronto’s Dalla Lana School of Public Health.
Jose Ancajima, left, carries the coffin on Saturday of his 10-year-old daughter, Fer Maria Ancajima, who died of dengue fever, in Catacaos District, Piura Department, Peru. (Ernesto Benavides/AFP/Getty Images)
How does El Niño make it worse?
The number of confirmed cases in Peru this year is already double that of 2017, when the World Health Organization declared a dengue epidemic in the country as a smaller El Niño effect caused heavy rainfall and flooding.
Fisman says El Niño can easily make an outbreak worse.
“More mosquitoes, more bites,” he said, explaining how an explosion in mosquito populations, due to optimal breeding conditions, also increases the virus “reservoir.” Because dengue mosquitoes infect more people, he said, uninfected mosquitoes pick up the virus from those people and then spread it further into the human population.
Further, the effects of El Niño are different around the world, and the elevated temperatures it causes can cause droughts that also boost mosquito populations — by turning running water into stagnant pools where they can breed.
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What can we learn from Peru?
There is, of course, no Earth-like “control planet” free of climate change to compare the changes taking place on Earth. But with El Niño — and the opposite, ocean-cooling pattern La Niña — occurring every two to seven yearsit may offer some insight into how extreme weather may affect the spread of viruses such as dengue, Fisman said.
“It’s kind of an experimental system that simulates what we expect to see increasingly under climate change scenarios,” he said. Climate change is also expected to affect the intensity of El Niño cycles.
But planetary warming, caused by El Niño or climate change — or both — will not only fuel mosquitoes’ reproductive cycles, they may also increase those mosquitoes’ range, McGill’s Libman said.
That range is expanding northward, which he says is concerning.
A health worker smokes mosquitoes to reduce the spread of dengue in a home, in the slum of La Primavera in Piura on June 3. (Martin Mejia/The Associated Press)
The Aedes mosquitoes are found in southern parts of the contiguous US, including Texas and Florida, although the number of locally transmitted cases is quite low.
Dengue-carrying mosquitoes are “not yet in Canada, but they’re not that far either,” Libman said.
Aedes aegypti mosquitoes, which are more likely to transmit diseases such as dengue to humans, are not present in Canada. Aedes albopictus mosquitoes, which can transmit dengue and other arboviruses to a lesser extenthave appeared in a small corner of southwest of Ontarioalthough there is no evidence that they carry exotic diseases.
Libman says that if global warming allows both types to thrive in traditionally temperate regions, there’s a possibility that arboviruses like dengue could adapt and perhaps spread more freely by Aedes albopictus mosquitoes.
He cited the example of the chikungunya virus, which was not present in the western hemisphere until 2013. Fisman says chikungunya was usually carried by the Aedes aegypti mosquito, but amended to the Aedes albopictus species and “spread like crazy in America where there was no immunity”.
“It’s not out of the question that the (dengue) virus will undergo changes at one time or another that will allow it to be transmitted even in a place like ours,” he said.
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