The outbreak is a warning sign for countries in the tropics, where dengue and other insect-born illnesses are increasingly prevalent as a rapidly changing climate brings more instances of warm and wet weather, which provide ideal breeding conditions for mosquito hosts. At its worst, dengue can cause high fevers, serious organ failure and death. The number of reported cases increased roughly tenfold from about 500,000 in 2000 to 5.2 million in 2019, according to the World Health Organization, which in March declared dengue a “major public health problem” for the Americas region.
The latest wave comes as northern parts of Peru experienced record rainfall in March. “In terms of climatic change, certainly increased precipitation, higher temperatures and higher humidity all favor the mosquito,” Raman Velayudhan, who leads the WHO’s program on Neglected Tropical Diseases, said at an April news conference.
The epidemic has been exacerbated by the beginning of the El Niño weather pattern, a regular occurrence that begins with warm water developing off the Pacific coast of South America and a weakening of trade winds that cause the water to flow toward the continent. This warming typically occurs every three to five years, before a period of cooler ocean water and stronger winds known as La Niña.
Climate change has increased rainfall expected during El Niño in Peru because more water evaporates into the air from a warmer ocean, which may then fall all at once when it reaches land, according to the U.S. Environmental Protection Agency, as opposed to less rain falling over a longer, steadier period of time.
Jason Mackenzie, professor of virology at the University of Melbourne’s Doherty Institute, said there is a clear link between increased rainfall and outbreaks of mosquito-borne illnesses. “Increased rainfall leads to increased accumulated water and so therefore you get more mosquitoes laying eggs,” he said.
A study published by U.S. and Peruvian public health experts in the journal PLOS Neglected Tropical Diseases last year found a “strong” link in Peru between dengue fever outbreaks, warmer weather and the El Niño Southern Oscillation.
“Dengue fever cases have increased substantially in the past four decades, driven largely by anthropogenic factors including climate change,” the authors wrote, adding that “climate change is expected to increase the frequency of El Niño events.”
Peru also prohibited storing still water in open containers, while rushing to opening a field hospital in one of its worst-affected regions. Residents have also been prohibited from trying to treat suspected dengue cases at home, and are instead being told to attend clinics.
“Dengue kills,” said Health Minister Rosa Gutiérrez Palomino in a Tuesday statement. “Because of that, help me eliminate mosquito breeding sites.”
Mackenzie, the Australian professor, said there have been several instances of increased rainfall leading to outbreaks of mosquito-borne illnesses in places where they were not known to spread. Japanese encephalitis has appeared 2,000 miles farther south than ever before — reaching Australia — after record flooding in usually cool and dry areas last year.
The West Nile virus also often resurfaces in the United States after a burst of mosquito breeding activity in a wet period, followed by a dry period that pushes mosquitoes into urban areas in search of water, Mackenzie said.
