“In an increasingly warmer and more populated world, mosquito-borne infections are becoming global diseases“, present even in parts of the planet that previously had at most imported cases. “If carbon emissions and population growth continue to increase at current rates, they will be at risk of malaria and Dengue 4 by 2100, 7 billion more people in the world”. The experts who will meet in Barcelona, Spain, from 27 to 30 April for the Congress of the European Society of Clinical Microbiology and Infectious Diseases (Escmid) are sounding the alarm. Global warming, they warn, it will also multiply the threat of antimicrobial resistance with a boom in antibiotic-resistant superbugs.
Two studies 'on display' at the Escmid meeting explain how theclimate change emergency is in fact a health emergency. The first will be presented by Rachel Lowe of Icrea in Barcelona, the Catalan Institute for Research and Advanced Studies. “The geographical map of vector-borne diseases has expanded rapidly in the last 80 years, with over half the world population at risk. But under the pressure of global warming and urbanization – infectious disease specialists predict – in the coming decades the epidemics of diseases carried by mosquitoes are destined to spread to areas of Europe, Asia, North America and Australia not yet affected by these infections.” Lowe states: “The harsh reality is that longer warm seasons will widen the time window for the spread of mosquito-borne infections, favoring increasingly frequent and increasingly complex epidemics to deal with”, especially in areas of the planet with “immunologically defenseless inhabitants and unprepared health systems”.
The data
Experts rattle off data. From 2000 onwards, they recall, the world has experienced 9 of the 10 hottest years for the spread of Dengue: the mosquitoes carrying the virus have invaded 13 European countries, with indigenous outbreaks also recorded in 2023 in France, Italy and Spain. Over the last 2 decades, the number of Dengue cases reported to the World Health Organization has increased 8 times, from 500 thousand in 2000 to over 5 million in 2019. The projections suggest two scenarios: “If the ambitious goal of containing global warming to 1°C, by 2100, compared to the period 1970-1999, we will have 2.4 billion more people in the world at risk of malaria and Dengue. But they will be double, something like 4.7 billion, if emissions and the planet's population will continue to grow following current trends.”
Analyzing extreme weather events in the Caribbean, Lowe found that periods of drought, followed 4-5 months later by excessive rainfall with warmer-than-usual temperatures, increase the likelihood of dengue outbreaks. “El Niño events”, the periodic climatic phenomenon associated with a strong warming of the surface waters of the central-southern and eastern Pacific Ocean, “which occur every 2-7 years – explains the researcher – make the climate warmer and humid, preparing the ideal conditions for epidemics of diseases borne by water and mosquitoes, with the proliferation of Aedes aegypti and Aedes albopictus species”, our 'tiger', “which spread the Zika and Dengue viruses”. For example, the Zika pandemic that hit Brazil in 2015, with 1.5 million people infected, is linked to El Niño. And fears grow considering that “the current El Niño is one of the strongest ever recorded”, a rare example of a “super El Niño”.
“With climate change looking so difficult to manage, we can expect to see more cases, and perhaps more deaths, from diseases such as Dengue and malaria across continental Europe,” Lowe predicts. “We must anticipate epidemics and intervene promptly to prevent them,” she urges. “Efforts must focus on strengthening surveillance, with early warning and response systems capable of more effectively directing available resources to the most at-risk areas, to control and prevent epidemics and save human lives.”
By combining weather forecasts and surveillance of insect vectors, science is developing methods to predict when and where epidemics could occur, so as to be able to concentrate preventive interventions in those areas. Lowe leads one of these projects: with the help of a powerful supercomputer and drones 'unleashed' to hunt for the most remote mosquito breeding sites, the goal is to anticipate epidemics in 12 countries. “We hope to give communities time to prepare and protect themselves. But the most effective way to reduce the risk of these diseases spreading to new areas – says the researcher – remains to drastically reduce emissions”.
There is also another way through which the climate emergency can impact infectious diseases. Moving on from superbugs: “Climate change is multiplying the threat caused by antimicrobial resistance, amplifying the growing risk through the increase in global temperatures, greenhouse gas emissions and rising sea levels”, the infectious disease specialists stated at the summit. The study on the topic will be presented by Sabiha Essack of the University of KwaZulu-Natal in Durban, South Africa.
“Climate change – he describes – compromises the ecological and environmental integrity of living systems and allows pathogens to cause more and more diseases”. In summary, “as temperatures increase” associated with global warming, “bacterial infection rates may increase and diseases may spread to higher altitudes and latitudes where they did not previously occur.” Some examples: “The increase in temperatures in water systems contributes to a better survival of Campylobacter, Salmonella and Vibrio”, bacterial species “which cause pathologies transmitted by water and food”. Again: “Candida auris”, the so-called 'killer fungus' which is also frightening in Italy, “has acquired tolerance to heat and salinity in wetland ecosystems. Escherichia coli and some of the Eskape bacteria” – an acronym which groups together Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter – already “grow optimally at 32-36°C” and are known to “escape antibiotics”.
“The increase in temperatures, incidence and prevalence of infectious diseases – Essack also observes – will increase the use of antimicrobial drugs and will consequently increase the selective pressure that favors the development of resistant species”. The researcher continues: “Climate change is then causing a shift in ocean currents, and with them the genes of antimicrobial resistance will also move. Even ballast water from ships is a possible vehicle of antimicrobial resistance across the seas.” What worries the expert above all are vibrios, marine bacteria that cause growing infections such as cholera: “An increase in sea surface temperature, due to climate change, can alter their abundance, distribution and infection patterns.” In short, “to face this threat – warns Essack – we need unequivocal political leadership and commitment, new evidence-based One Health strategies and targeted interventions to be adapted to national contexts”.
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