With the Earth warming and the range of tropical sicknesses transmitted by mosquitoes expanding, the U.N. health agency finds scientific studies often fail to assess the full impacts of human-induced climate change on malaria, dengue, trachoma and other tropical vector-borne diseases.
A review by experts for the World Health Organization and Reaching the Last Mile of more than a decade of published research on how climate affects malaria and neglected tropical diseases, or NTDs, points out a concerning bias. The review finds the research focuses on wealthier countries with low disease rates and high access to quality health care.
"It is difficult to have immersed ourselves in this literature as we have without acquiring a deepened sense of foreboding over the adverse influence that we as a species are visiting on our planet and its most vulnerable people," lead author Petra Klepac of Oxford University's Big Data Institute and 69 co-authors conclude in an article published this month in Transactions of The Royal Society of Tropical Medicine and Hygiene.
"Women, children, older people, Indigenous groups and ethnic minorities, migrants and the very poor have contributed least but are likely to experience most of the effects of the climate crisis, notably including through any increase in the burden of malaria or NTDs," they wrote.
NTDs are a group of 20 conditions caused by a variety of pathogens, including viruses, bacteria, parasites, fungi and toxins. Many of them are vector-borne and are associated with complex life cycles, WHO says.
Globally, they still affect 1.6 billion people, mostly poor, marginalized populations, though efforts to eliminate several diseases, such as dracunculiasis (Guinea-worm disease), onchocerciasis (river blindness), lymphatic filariasis (elephantiasis), and trachoma, are paying off. They are considered “neglected” because they receive less attention and funding compared to HIV/AIDS, tuberculosis and malaria.
Medications and treatments for NTDs and the means of prevention are readily available in most of the world, but lower-income nations lack equal access. The authors note, however, "an emerging opportunity to correct this inequity arises through financial commitments to NTD control and elimination" that nations pledged at the U.N. climate summit in Dec. 2023.
"Allocation of these resources should be guided by informed scenario analyses of current and future disease burden," they wrote. "The work described in this review is a start; convening stakeholders globally to advance the research agenda must be our next collective move."
Linking climate and disease
Vectors – typically bloodsucking insects such as mosquitoes, ticks and fleas – are living organisms that can transmit infectious pathogens between humans or from animals to humans. Rising temperatures and changing weather patterns alter the spread of vector-borne diseases, significantly affecting human health and further straining health care systems.
The review by WHO and RLM, a global health initiative aimed at eliminating preventable diseases and funded by Sheikh Mohamed bin Zayed Al Nahyan, president of the United Arab Emirates, scoured peer-reviewed papers published between Jan. 2010 to Oct. 2023 for data on national disease burdens, access to health care, and climate vulnerability.
The available research tends to focus on malaria, dengue, and chikungunya, which are among the most common mosquito-borne diseases worldwide, while leaving other NTDs significantly underrepresented, their review found. It also revealed a lack of understanding of how human-induced changes to climate patterns impact malaria and NTDs – causing the range of diseases to expand.
“The findings presented in this major review highlight the need for more comprehensive, collaborative, and standardized modelling, so that we can better understand and predict the effects of climate change on malaria and NTDs, both directly and indirectly,” said Dr. Ibrahima Socé Fall, head of WHO’s NTD program and leader of the study.
"Malaria transmission is likely to shift both polewards and to higher altitude, while the mosquito vector responsible for transmission of dengue and chikungunya is predicted to continue to expand its range," he said. "If we are to protect and build upon the hard-won victories of the past two decades, the time to mobilize is now.”
Poorer nations are the most impacted
With the Earth's warming making conditions more favorable for disease-carrying pests, vector-borne diseases account for more than 17% of all infectious diseases and cause more than 700,000 deaths a year, according to WHO.
In East Africa, for example, malaria is being reported in highland areas of Kenya, Ethiopia, and Uganda, regions that historically had low incidences due to their cooler climates.
Parts of South America’s Amazon basin also are seeing a resurgence of malaria as deforestation, combined with higher temperatures and changing rain patterns, create ideal breeding grounds for mosquitoes.
Similarly, in South and Southeast Asia, increased temperatures and altered rainfall patterns are extending the transmission season and expanding the range of malaria into previously unaffected areas.
Northern climates, such as those in Europe and the United States, are not immune, with warmer weather creating conditions that could facilitate the re-emergence of malaria where it had been largely eradicated. Cases of locally transmitted malaria already have been reported in Greece and Italy and in the U.S. states of Texas and Florida.
“We have recently seen the consequences of extreme weather events on malaria, and they are only predicted to become more commonplace,” said Dr. Daniel Ngamije Madandi, head of the WHO’s Global Malaria Program and a former Rwandan health minister.
“As the impact of climate change is likely to be disproportionately borne by the poorest people, who are also disproportionately affected by malaria and NTDs," he said, "a more equitable, comprehensive and sustainable response is needed."
Vector-borne disease at a glance:
