Extreme Weather Helped Fuel Surge in Malaria Cases Last Year

Jahi Chikwendiu/The Washington Post
Doctors and medics-in-training discuss a malaria case in the severe malaria ward of the Nametil Health Center in Nametil, Mozambique, on Aug. 9.

The number of malaria cases worldwide surged by millions last year, the World Health Organization said Thursday – a change driven by extreme weather events such as catastrophic flooding in Pakistan, as well as other conflicts and humanitarian crises that allowed the deadly disease to proliferate.

The WHO said the spike came after a two-decade stretch beginning in 2000 that saw global cases of malaria fall from 243 million to 233 million, despite population booms in many parts of the developing world.

But in recent years, the agency said, the global case count “was significantly higher than before the pandemic.” There were an additional 11 million recorded cases in 2020, followed by no change in 2021, then an increase of 5 million cases in 2022, the most recent year for which data are available – resulting in about 249 million cases worldwide.

“Malaria is not a disease where you can keep a steady path. You’re either winning against it, or you’re losing,” said Peter Sands, the Executive Director of The Global Fund. “At the moment we’re at a crux where we’re certainly not winning as much as we would like to be.”

According to the WHO, the wave of additional cases logged between 2021 and 2022 were concentrated largely across five countries.

Pakistan, where hundreds of people died and millions were displaced by unprecedented flooding, saw the largest rise in malaria, with 2.1 million cases during that time. The case incidence jumped fivefold there, health officials said, from 2.2 to 11.5 cases per 1,000 people at risk in the country. Ethiopia and Nigeria each saw an increase of about 1.3 million cases over the same time period, followed by Uganda and Papua New Guinea.

Malaria deaths worldwide decreased to 608,000 in 2022 from a recent high of 631,000 in 2020, but they still hovered above pre-pandemic totals. Most malaria deaths are in children under the age of 5.

“What we and our partner countries see every day, right now, are concrete changes that are affecting our work programmatically and putting more people at risk,” David Walton, the U.S. global malaria coordinator for the U.S. Agency for International Development, said in a statement.

“It is a painful reality that the communities least responsible for climate change are the ones most vulnerable to its impacts,” he said.

Thursday’s report makes clear that many factors can shape the rise or fall of malaria, a potentially fatal disease caused by a parasite that commonly infects a certain type of mosquito that feeds on humans. They include political unrest and conflict, humanitarian crises, lack of funding and resistance to front-line medications. The lingering impacts of the coronavirus pandemic and the interruptions it caused in health care access also played a role.

But, the WHO underscored, Earth’s warming climate is likely to have profound effects, both directly and indirectly, on malaria transmission.

While data on the long-term impact of climate change on the spread of malaria is “sparse,” the agency said, there is reason to believe that a hotter world will only fuel the spread of such diseases.

Scientists have detailed how extreme weather disasters are becoming more intense and common. In Pakistan during 2022, for instance, warming caused glaciers to melt and rivers to surge in the north of the country. Heating of the Indian Ocean contributed to torrential rainfall in the south.

Extreme floods drive people from their homes, exposing them to the elements and mosquitoes. The standing water left behind creates an ideal mosquito breeding ground for months. The water also damages health care facilities and cuts off transportation, leaving sick people without means of treatment.

“The places that are most affected are the places that have the least infrastructure to respond to these sorts of events,” said Ross Boyce, an assistant professor of medicine and epidemiology at the University of North Carolina School of Medicine. “I do think it’s going to become an increasing contributor to global malaria burden.”

Extreme weather events are merely one example of the type of challenges that could lie ahead.

“Climate change threatens the complex relationship between natural and human systems and undermines many of the social determinants of good health – such as livelihoods, nutrition, security and access to quality health services,” Thursday’s WHO report states. “It is a both singular threat to health and a ‘threat multiplier.'”

A recent Washington Post analysis found that climate change and demographic growth could put more than 5 billion people at risk for malaria by 2040, imperiling decades of global progress against the disease.

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 Post analysis of climate modeling data and reporting from the southern African country of Mozambique.

Health data obtained and analyzed by The Washington Post detailed how dire the situation is becoming in particularly vulnerable places. In Mozambique, cases are on pace this year to reach their highest level since 2017, when the government began its current process for counting cases.

The Post analysis details which countries and regions face the most acute 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 2070.

“Efforts to fight malaria are at this crossroads and have been seriously challenged by climate change,” Sherwin Charles, the co-founder of Goodbye Malaria, which has been working to end malaria in southern Africa, told The Post this year. “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.”

In the United States, warming temperatures and increased rainfall are projected to lengthen malaria transmission seasons across the South. In June, five locally transmitted cases were discovered in Texas and Florida; they were the first cases acquired in the United States in two decades. Once endemic, malaria was eliminated in North America and Europe in the mid-1900s as officials gained a better understanding of how to control it.

The disease has remained widespread in sub-Saharan Africa, but did experience notable declines in incidence and mortality rates in the 2000s following a multibillion-dollar health campaign led by Western governments and international nonprofits. Those efforts prompted the widespread use of insecticide-treated bed nets, quick tests and more readily available treatments.

Some of the gains in Africa have been reversed since 2017, and experts say this trend is likely to continue, although advances such as improvements to the malaria vaccine could brighten the outlook in years ahead. Researchers and government officials attribute some of the ongoing challenges not simply 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.

While scientists continue trying to better understand how climate affects malaria transmission, they know that the parasites and the mosquitoes that transport them tend to thrive in warm, humid and rainy conditions. The insects do best when temperatures are around 80 degrees Fahrenheit.

And in a steadily warming world, more places are becoming suitable for the disease and the vector that spreads it.

The combination of extreme weather disasters, scarce resources, political strife, biological threats and inadequate access to health care have left the aspiration of a malaria-free world “still far from reach,” the WHO said Thursday.