Unica Cardoso leaned against the walls of the overcrowded health center, her body aching and her fever spiking.
It was Mozambique’s winter season, when cooler and drier weather have historically meant less malaria transmission. But there’d been so many suspected cases that day that the health center had run out of quick tests. Cardoso, 35, had just tested positive and feared her 2-year-old daughter at home was sick with the same.
“I am not surprised anymore,” she said of falling sick during the winter. “But it is not normal.”
The threat posed by malaria stands to soar as the planet warms because of longer transmission seasons, more frequent and severe extreme weather events, and the migration of malaria-carrying mosquitoes to new latitudes and altitudes, according to a Washington Post analysis of climate modeling and reporting from the southern African country of Mozambique.
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Health data obtained and analyzed by The Post reveals how dire the situation is becoming, with Mozambique’s malaria cases on pace this year to reach their highest level since 2017, when the government began its current process for counting cases.
The results of the Post analysis reveal which countries and regions are at most risk, in particular as seasonal changes benefit disease-carrying mosquitoes. In some regions of the world, transmission seasons could increase by up to five months by the year 2070.
Sub-Saharan Africa has long faced the highest risk from malaria, with some regions seeing transmission seasons all year. Hot spots for malaria transmission are emerging at higher altitudes and latitudes.1 / 4
In the United States, warming temperatures and increased rainfall are projected to lengthen malaria transmission seasons across the South. Once endemic, malaria was eradicated in the United States last century.1 / 4
Hotter temperatures are allowing these mosquitoes to spread in areas where malaria has not historically been a problem, especially in the Andes Mountains of Colombia, Peru and Ecuador.1 / 4
In the highlands of African countries such as Ethiopia and Kenya, where the population has little resistance to the disease, currently short transmission seasons could stretch up to four months a year.1 / 4
Sub-Saharan Africa has long faced the highest risk from malaria, with some regions seeing transmission seasons all year. Hot spots for malaria transmission are emerging at higher altitudes and latitudes.
In the United States, warming temperatures and increased rainfall are projected to lengthen malaria transmission seasons across the South. Once endemic, malaria was eradicated in the United States last century.
Hotter temperatures are allowing these mosquitoes to spread in areas where malaria has not historically been a problem, especially in the Andes Mountains of Colombia, Peru and Ecuador.
In the highlands of African countries such as Ethiopia and Kenya, where the population has little resistance to the disease, currently short transmission seasons could stretch up to four months a year.
The Post analysis relied on data produced by three models that estimate how long each year conditions are favorable for mosquitoes and parasites in given areas, by projecting how the heat, humidity and precipitation would change in coming years, and how much of the human population is at risk in each of them. The Post averaged the data to account for differences among them.
While infectious-disease experts have for years documented that rising temperatures expand the range of deadly pathogens, the ominous trend here underscores the extent to which nearly two decades of global progress against malaria is being eroded in part because of climate change. The world has seen global case counts ticking up over the past six years, according to the World Health Organization, with case rates increasing by 10 percent during that period in Mozambique, which researchers rank among the countries most vulnerable to climate change.
“Despite all the interventions, we are not seeing results,” said Baltazar Candrinho, who leads Mozambique’s national malaria control program. “The temperatures are going up, the rainfall is strange … and when a cyclone comes, people lose everything — and we lose the tools to fight malaria. It is a big challenge.”
Malaria carried by these mosquitoes is part of an accelerating wave of sickness and death due to climate change. Humanity is increasingly confronted with lethal heat, malnutrition linked to ever more common droughts and floods, and illnesses borne by mosquitoes and ticks — including dengue, Zika and chikungunya. Malaria, alone, was responsible for more than 600,000 deaths worldwide in 2021, the last year for which data was available, and more than three-quarters of the victims were under the age of 5.
In some countries where malaria is already endemic everywhere, such as Mozambique, case counts are on the rise in part because climate change is disrupting traditional rainfall patterns and causing extreme weather events, in turn fostering conditions in which mosquitoes thrive and breed, such as standing water and humidity. Other nations could have areas that experience shorter transmission seasons, as they become so hot and dry that it will be harder for mosquitoes to survive.
Mozambique and other countries with the highest malaria case totals also have some of the world’s fastest-growing populations. By 2040, the combined effects of longer transmission seasons and demographic growth could put more than 5 billion people at risk of contracting malaria worldwide, including a billion on the continent of Africa alone. In Mozambique, that figure could reach 29.5 million people. By 2070, this population could increase to 1.5 billion in Africa, and in Mozambique, it could reach 42 million people — more than 75 percent of the projected total population of the country, the Post analysis shows.
In the health center in Nametil, a rural town in Nampula province where the Post analysis shows that malaria case rates increased 43 percent between 2017 and 2022, Cardoso wove her way through crowds of other patients, many of them sick with malaria and all waiting for medicine. Already, she had lost three children to malaria, all before their fifth birthday.
She walked quickly, eager to get back to her daughter, who she feared might have grown sicker in her absence. Cardoso, a petite woman with expressive eyes, said she had wanted to bring the girl to the clinic that day but had neither the money for medication nor the strength to carry her.
She passed a door with a poster that reminded patients: “Families who are protected from malaria smile together forever.”
The malaria parasite typically spreads when a female mosquito in the Anopheles family bites a person who is already infected. The mosquito takes in the parasite along with the human blood and, about a week later, can transmit malaria by biting another person.
Scientists are trying to better understand how climate affects malaria transmission but know that the parasites and the mosquitoes that transport them tend to thrive in conditions that are warm, humid and rainy. The insects do best when temperatures are around 80 degrees Fahrenheit.
Endemic malaria was eliminated in North America and Europe in the mid-1900s, with a better understanding of how to control it. The disease has remained widespread in sub-Saharan Africa but saw dramatic declines in case and mortality rates in the 2000s following a multibillion-dollar health campaign led by Western governments and international nonprofits that prompted the widespread use of insecticide-treated bed nets, quick tests and more readily available treatments.
Some of those gains in Africa have been reversed since 2017, and experts say this trend is likely to continue, although gains in development and technological advances, including improvements to the malaria vaccine, could improve the outlook. Researchers and government officials attribute this troubling trajectory not only to climate change but also to the increased resistance of mosquitoes to insecticides and of the parasite to drugs. Improved disease surveillance and data collection could also be contributing to higher case counts.
The projections for South America are also grim. There, 330 million people could be at risk of contracting malaria by 2070. The projections take into account changing climate and demographic factors but do not factor for public health efforts or mosquito control programs.
“Efforts to fight malaria are at this crossroads and have been seriously challenged by climate change,” said Sherwin Charles, the co-founder of Goodbye Malaria, which has been working to end malaria in southern Africa. “We thought we knew how to deal with this epidemic, but the complication of climate change brings different factors to bear that maybe we are not ready for.”
Tatiana Marrufo, a doctor who studies climate change and disease at Mozambique’s National Health Observatory, said that the same environmental conditions that foster the breeding of mosquitoes can also often handicap efforts to contain malaria.
Nonprofits, for instance, try to spray insecticide inside homes in advance of the rainy season, but erratic rainfall is making it hard to time effective spraying. Additionally, cyclones and floods can wipe out a family’s supply of bed nets in seconds and force them out of their homes, leaving them more exposed to mosquitoes.
Longer transmission seasons
Outside the low-slung Nametil health center on an August morning, the skies were foreboding, clouds heavy. Even though August is typically cold and dry, within the hour, rain would begin to fall. The warm and rainy season, so predictable for generations, has turned capricious, offering little respite from malarial mosquitoes.
“Malaria used to come in a certain period — the rainy, hot season,” said health coordinator Adamo Palame, who works for Doctors Without Borders raising community awareness about how to control malaria and other tropical diseases, punctuating his words with emphatic hand gestures. “But right now, throughout the year, the mosquitoes multiply.”
“Even when you think you are in the dry season,” he added, eyebrows arching above his round-rimmed glasses, “all of a sudden, it rains.”
In front of the clinic’s triage center, Joca Formiga, a mother of seven, held a quick test in her hand. Two pink lines indicated that her 2-year-old daughter had just tested positive for malaria. In her other hand was a yellow booklet in which doctors had marked each previous positive result. This was the fifth time her daughter had tested positive, just this year.
Within two minutes, another woman whose child had tested positive joined her. Then another, then another, until a dozen women with babies swaddled on their backs and tests in their hands had gathered round.
“I cry within my heart,” said Olga Victorino, “and ask myself, ‘Why do my children have malaria again and again and again?’”
Victorino, 25, a short woman in a yellow wrap, held her crying 2-year-old son, who had just tested positive. There was more malaria now than when she was growing up, she said. She suspected it might have something to do with the weather, especially the water that no longer seemed to recede.
“If it rains, it is difficult to stop their infiltration,” Victorino said of the mosquitoes. “The pools of water are everywhere.”
Historically, malaria cases peaked once each year in Mozambique, around February or March, according to Abuchahama Saifodine, a country adviser to the U.S. Agency for International Development who grew up in Mozambique and has long studied malaria. But in recent years, he said, rain is so erratic that in some parts of the country, there are now two or more peaks.
Mozambique’s extended transmission season could be a harbinger for other parts of the world.
In the United States, for example, where broad land-use changes and public health initiatives helped eradicate malaria in the past century, the changing climate could create favorable conditions for the disease to spread if travelers arrive carrying the parasite. Warming temperatures and increased rainfall are projected to lengthen the period when malaria could propagate across the South. Portions of North Carolina, Tennessee and Virginia could see transmission seasons of at least four months by 2070.
More than 200 million people, many without acquired immunity, could be at risk, according to the Post analysis.
“The fact that [malaria] will be affecting immunologically naive populations means that there’s going to be higher morbidity and likely higher mortality within those populations,” said Felipe Colón-González, lead author of the Lancet study evaluating the malaria models on which The Post based its analysis.
“And the fact that the health systems in those areas are unprepared for that means that they will have to change the allocation of resources that might already be scarce in some areas of the world,” added Colón-González, an infectious-disease modeler with Wellcome, a nonprofit that supports global research in health and climate.
After returning to her one-room concrete home, Cardoso, who had tested positive at the health center on that August afternoon, said she was determined to find the strength to bring her daughter for treatment and to find the money — the equivalent of about 9 cents — to pay for medication at the public clinic. (At the private clinic, each dose costs the equivalent of $5 — a prohibitive amount in a province where the average wage is less than $1 a day.)
Each night, Cardoso said, she carefully stretches nets over her three surviving children as they sleep. But the house’s walls cracked during the most recent cyclone, she said, and mosquitoes are also able to get in through a hole in the roof.
“I don’t know what is causing the change in the weather,” she said, stroking her little girl’s hair. “But there are more mosquitoes now, and every month, these children are getting sick.”
Alberto Charles shook his wife awake one night early this year after being awakened by the sound of rushing water. The couple and their children had only 10 minutes to grab what they could, including a freezer, a radio and a few sets of clothes, as water filled their home. When they left, the water was already knee-deep. Outside, the floods had ripped their orange trees and banana plants out of the ground.
A few weeks later, when Charles and his family were still sheltering at a crowded emergency center surrounded by stagnant water, chills started to rack his body. Then, he lost his appetite, and the fever set in. When he went to the health center in Boane district, about 20 miles southwest of the capital, Maputo, there was a long line of people waiting to be tested for malaria.
Like much of southern Mozambique, Boane is wealthier and more developed than much of the north, including Nametil. The malaria rates are also dramatically lower here because of the climate, higher level of development and a years-long anti-malaria campaign, led by Goodbye Malaria, which provides bed nets and sprays insecticide inside and outside homes.
But Olivia Chissaque, the head doctor at the Boane Health Center, said the flooding upended that progress, with case rates afterward jumping to where they had been years earlier. And treating the patients was more difficult, she explained, because many of the doctors and nurses had lost their homes.
Globally, extreme weather events driven by the burning of fossil fuels are becoming more common and more intense. Mozambique, which has more than 1,500 miles of coastline, is especially vulnerable to cyclones, which studies show have become fiercer in recent years. Government officials say extreme flooding in Mozambique has also surged, including the destruction in Boane this year, when roads turned to rivers and thousands were displaced.
Beyond the immediate damage caused by cyclones and floods, malaria and other diseases such as cholera tend to surge weeks later due to extensive standing water and the disruption of disease control efforts. Teams from Goodbye Malaria had just completed indoor spraying when the floods arrived, washing away the spray — and sometimes entire houses.
Alberto Charles, 34, said that within hours of the floods starting, his entire house had been submerged except for the antenna on the roof.
His family eventually returned home, though he said he worries that mosquitoes are breeding in the stagnant water still sitting in their fields six months later, and he’s nervous because his house has not been resprayed. But Charles, his face tired and his clothing worn, said there was no choice but to return.
“We don’t have anywhere else to go,” he said.
Each year, Tatiana Marrufo leads an effort at Mozambique’s National Health Observatory to predict where outbreaks will occur. Her team has been surprised in recent years, she said, to see upticks in malaria in some of the country’s highest-elevation districts.
Typically, higher altitudes have been associated with lower temperatures that are not suitable for malaria-carrying mosquitoes. But a recent study by researchers at Georgetown University found that the range of such mosquitoes in Africa extended to higher elevations at an average of about 6.5 meters per year — more than 200 feet per decade — during the past century.
Other studies have established the link between rising temperatures and the expansion of malaria epidemics to higher altitudes during particularly warm years and those associated with El Niño.
Areas at the edges of malaria’s current reach, such as those at higher altitudes, are the places where climate change and variability are having the largest impact, said Mercedes Pascual, a biology professor at New York University who studies the ecology and evolution of infectious disease. Some of those areas, Pascual noted, are highly populated regions in the highlands of East Africa.
Marrufo and her colleagues are studying whether the higher-altitude outbreaks they are seeing in Mozambique might be linked to this global trend. She noted that malaria has always been present in these areas, which are not nearly as high as more mountainous regions in Africa, but she still suspects the rising case counts could be a product of climate change.
The district of Mandimba in northwestern Mozambique is one of the higher-altitude jurisdictions in that part of the country. Since 2017, Mandimba has seen a 20 percent increase in malaria case rates, government data shows.
Lucia Eduardo, 36, a community health worker in Mandimba, said that malaria was less of a problem when she was a girl, even though her remote community knew less about combating the disease. Already this year, she said, two of her children had fallen ill with malaria. She and others here said they suspected that part of the reason was that the weather has gotten hotter.
In winters past, Mandimba residents would typically be layered in sweaters, but in recent years, they are comfortable at times in T-shirts, Eduardo said. And during the hot season, people now sometimes sleep outside, introducing an additional risk of contracting malaria.
Since 2014, Eduardo has worked with a community group to spread awareness about the disease. The group is run by a local nonprofit and funded by USAID’s President’s Malaria Initiative, which along with the Global Fund provides the vast majority of Mozambique’s funding for malaria prevention.
Wearing a skirt bearing the words “Zero malaria starts with you,” Eduardo said she goes door-knocking every few weeks, explaining how to prevent the disease from spreading. She said she wishes those efforts were paying off better.
“It is a permanent challenge,” she said, looking up, her eyes bright. “And when there is such a challenge, I will do everything I can to save my community.”
About this story
Design and development by Hailey Haymond and Emily Sabens. Additional development by Yutao Chen. Editing by Alan Sipress, Anu Narayanswamy, Olivier Laurent, Monica Ulmanu, Juliet Eilperin, Joe Moore, Emily Morman, Tom Justice and Jay Wang.
The Washington Post analyzed data on malaria counts and deaths on a global scale and in particular for the country of Mozambique. The global modeled data projects which areas of the world will be most suitable for malaria-carrying mosquitoes based on various climate and emissions scenarios and how many people in those areas will be at risk of contracting the disease in the future.
The climatic suitability and population-at-risk data came from a set of three peer-reviewed models that eight scientists from European medical and research institutions published in the journal the Lancet Planetary Health. The models each accounted for different sets of variables, such as temperature, precipitation, humidity, local hydrology, mosquito populations and the potential immunity to malaria that had built up in the human population in an area. Using these variables, the scientists determined which areas of the planet might be suitable for mosquito and parasite reproduction and for how many months during the year. That measurement is called length of malaria transmission season.
To analyze malaria case trends in Mozambique, The Post acquired detailed monthly counts by district from the country’s National Malaria Control Program. The data range from January 2017 through August 2023.
Global malaria case and death counts come from the World Health Organization’s World Malaria Report and cover 2000 through 2021.
How we are projecting the length of malaria transmission seasons in 2040 and 2070
The modeled data were produced for the entire globe on a 35-square-mile grid. For each square, the scientists calculated the number of months per year that area would be suitable for malaria transmission as well as the number of people at risk for contracting malaria. They produced the data in 30-year slices from 2010 to 2100. The Post used the slices ranging in years from 2010 to 2039 and 2040 to 2069. The models measure the changes and transmission season and population at risk relative to a base period of 1970 to 1999.
The Post averaged the data produced by the three different models for a specific scenario for future greenhouse gas emissions — RCP 4.5 — which is deemed a middle-of-the-road approach. The Post then aggregated the data by country to determine which specific places could be most at risk by 2070.
Adrian Tompkins and Cyril Caminade, scientists at the International Centre for Theoretical Physics in Trieste, Italy, who helped develop two of the malaria models and ran the simulations, guided reporters on how to analyze the data and interpret results.