Climate change is aggravating the spread of infectious diseases

By - Integrated Care Journal

Climate change is aggravating the spread of infectious diseases

ICJ Editor Francesco Tamilia spoke with several infectious diseases experts to understand how climate change impacts the transmission of infectious diseases and what can be done to minimise and mitigate their impact on people’s health.

“When doctors transferred me to another room, alongside patients in a terminal condition, that’s when I accepted I was going to die. I could see the fear in the faces of the people around me, doctors just kept doing more and more tests on me. I remembered thinking: ‘I am only 17, am I dying? ’”

When Ana first became sick with a high fever, she did not give it too much importance, it was nothing new to her. Then, her temperature rose higher and higher, she became weaker and did not have enough energy to eat or walk.

“I remember trying to walk to the kitchen when I suddenly fainted. That was the moment my mother realised that there was something wrong with me,” Ana recalls.

From the moment she was brought to the hospital, doctors realised she needed treatment. However, due to her young age, doctors were initially not sure what was causing the deterioration of her health.

Ana regained consciousness but her platelets were plummeting at an alarming rate – so fast that she was transferred to a secure room to avoid possible in-site infections that could turn out to be fatal for her while she was is such fragile state. After an initial wrong diagnosis of leptospirosis, doctors identified her illness as the mosquito-borne viral disease dengue.

Climate change and infectious diseases

Dengue is just one of the many infectious diseases that have proliferated in recent years due to climate change. Several recent studies have shown how a changing climate is aggravating the negative health impacts of several infectious diseases by broadening the range of vectors that spread them.

The Lancet Countdown 2020 annual report found that “changing climatic conditions are increasingly suitable for the transmission of numerous infectious diseases”. The report revealed that the global climate suitability for the transmission of dengue increased significantly between 1950 and 2018.

According to the World Health Organization (WHO), there are an estimated 100-400 million dengue infections each year and about half of the world's population is now at risk. The 2020 UN report Preventing the next pandemic, has also defined climate change as a “major factor” in disease emergence, arguing that “the survival, reproduction, abundance and distribution of pathogens, vectors and hosts can be influenced by climatic parameters affected by climate change. ”


The situation in continental Europe is no exception to the increasing suitability of infectious diseases. Various infectious disease outbreaks have been reported in different countries including an outbreak of chikungunya fever in Italy in 2007, West Nile fever in Greece and Romania in 2010, and the first local transmission of dengue fever in France and Croatia in 2010. In 2019, the European Centre for Disease Prevention and Control (ECDC), which now ranks climate among the biggest drivers of infectious disease, reported a total of 4,363 cases of dengue in the EU/EEA.

In 2012, Jan Semenza, Head of the Health Determinants Programme at ECDC, worked on a paper trying to assess which infectious diseases are impacted by climate change.

The results indicated that some infectious diseases are strongly associated with climate. Jan tells Integrated Care journal that: “Once we found links between certain infectious diseases and climate change, we then established a risk assessment which gave us a feeling for which diseases are of concern if they're associated with climate change and if the impact on society is significant. The diseases that we identified to be at elevated risk were Lyme borreliosis, dengue fever, tick-borne encephalitis, Rift Valley fever, chikungunya fever, Vibrio and leishmaniasis."


Aedes albopictus, also known as the Asian tiger mosquito, can transmit dengue, chikungunya and Zika. The world’s most invasive mosquito, it became established in Italy in 1990 and subsequentlyspread to several other EU and neighbouring countries.


The research, which identified climate change as one of the main drivers in making Europe a “hot spot” for emerging infectious diseases, called for changes in the monitoring system. Since the paper was published, many of the climate-sensitive infectious diseases found to be a risk in the EU were put under surveillance.

There are also some predictions that climate change is going to make some areas inhospitable for some vectors or the transmission of the pathogens, thus resulting in a decline in risk.

“We know that there are some new risks appearing in some places and some risks may be disappearing in others. But what we don't know now is the net balance of those increases and decreases in risk,” says Kris Murray, an Associate Professor of Environment and Health at Imperial College London.



Inequalities and awareness of climate-sensitive infectious diseases

Like many other public health issues, it is expected that climate-related changes in the distribution of infectious diseases will represent a greater burden for those who are already suffering from other public health issues.

Research shows that the health problems associated with climate change are amplified by the lack or limited access to healthcare, especially in poor communities. This was also confirmed by Murray: “We would expect the new risks, the novel risks that are being presented by climate change to be magnified in those areas where the existing risks are already concentrated and in countries that have a weaker health infrastructure”.

A global survey published in 2020 by PLOS One, which assessed the perception and knowledge of the effect of climate change on infectious diseases within the general public, found clear evidence that the public is not fully aware of the role of climate change on infectious diseases.

Nearly 50 per cent of the respondents in the study did not understand the link between climate change and infectious diseases. However, some countries have already started working on raising awareness of the impacts of climate change on infectious diseases. Canada is one of them.

“There are many initiatives starting up in Canada around climate change and infectious diseases. One of the goals of the Public Health Agency of Canada's Infectious Disease and Climate Change Fund is to help healthcare providers learn how to deal with infectious diseases that they may never have seen before.

“The Canadian Association of Schools of Nursing has recently put together an online learning module around zoonotic, and climate-driven infectious diseases and how nurses can identify them, learn, advocate for their patients and do the treatment,” says Gillian Pritchard, Project Officer of the Canadian Public Health Association.


“It is unequivocal that humans have changed the climate, and it is unequivocal that that is now changing life on Earth as we know. It is changing animal distributions and it is contributing to biodiversity loss. And this is changing the landscape of infections. ”

– Kris Murray, an Associate Professor of Environment and Health at Imperial College London


Canada’s work on raising awareness goes beyond health professionals. They have also organised initiatives to aimed to fill the knowledge gap within the general public. Among those, the Canadian Public Health Association has organised a poster contest for children to help them “learn more about climate-sensitive infectious diseases, and share awareness and prevention information with their friends, family and communities. ”

“We really wanted to raise awareness around the effects of climate change on infectious disease for people across Canada and make it relevant for them no matter where they live in the country,” says Pritchard. “At that age, they're learning enough about science to grasp those connections between the climate change and health and how it can affect them. A poster contest is fun and arty, and a really good way to get them involved and start putting together those concepts,” she adds.

Looking for solutions

Climate change is clearly having an impact on some infectious diseases and consequently on people’s health. But what can be done to minimise and mitigate these dangerous effects?

According to Semenza, increasing disease monitoring in what he called “21st-century surveillance” can play a crucial role. “We are trying to come up with a paradigm shift instead of looking at the disease per se. We want to look at epidemic and climate precursors of disease. Is it possible for us to detect a signal in the environment or in the climate that can predict an increase in the disease? ” Semenza wonders.


“Climate change is already here. And I believe very strongly that it is here to stay. We need to learn to minimise those public health impacts by acting proactively, trying to reduce those risks. ” 

– Jan Semenza, Head of the Health Determinants Programme at ECDC


This approach was successful in the surveillance of Vibrio, water- and food-borne bacteria that have a case fatality similar to Ebola. 50 per cent of people that get septicaemia or wound infections are at risk of dying. According to a research by the University of Bath, these pathogens grow in warm, brackish waters, and climate-change driven alterations in seawater temperature and salinity alter its abundance, distribution, and patterns of infection. Once a sea surface temperature passed the 15 degrees threshold, they start to multiply and proliferate, resulting in lots of people getting infected.

To minimise those health impacts of Vibrio, Semenza and his team went on and developed a system that monitors the sea surface temperature and salinity in any ocean throughout the world with satellites.

“We can see a five-day forecast and, if certain conditions are met, we send out alerts to the local health officials to make them aware of the potential risk in this area. Local officials can then take public health actions such as closing the beach and leting the physicians know that they should look out for infections. This kind of an early warning system allows us to intervene before we see the impacts,” says Semenza.

To tackle the climate crisis, including the impacts of infectious disease on people’s health, we need a very coordinated multi-sectoral approach, as opposed to addressing “one crisis” at the time, in Murry’s mind . “In that action of reducing emissions, as an example, we also have co-beneficial outcomes for human health,” he says.



A health crisis

Fortunately, Ana was able to recover from the infection and was discharged from hospital after those terrible moments that, in her own words, “left a mark in her life”. However, dengue remains very common in the region where she grew up in Colombia. In the past year, Covid-19 and dengue outbreaks have left the region on its knees.

According to the policy report: Responding to the health risks of climate change in Europe, dengue is the most rapidly spreading vector-borne disease with steady growth in incidence at a global scale. “Epidemics of dengue not only result in human suffering and lives lost but also translate into unexpected challenges to health services, as well as significant economic losses from both increased healthcare demand and loss in labour,” the report says.

Ana now works as Events Manager for a restaurant in London. When confronted with the expert reports that predict increases in dengue infections in Europe due to climate change, she warns to be very scared. What’s most worrying to her is the lack of awareness of this disease among European people, as opposed to in Colombia where people have been living with the disease for years and are more aware.

Although the risk of dengue remains real in Europe, Semenza believes that we will not see massive dengue outbreaks as they have seen in other parts of the world such as in Asia and Sri Lanka.

The Covid-19 crisis and the development of world-saving vaccines in record time have shown humanity’s strength and ability to overcome a common enemy. However, this may not be enough compared to another, and perhaps greatest threat to humanity: the climate crisis. Scientists tell us that if we reach the point of no return, climate change will most likely trigger an 'ocean of crisis'.

Rather than playing Russian Roulette with our future, it is clear the only solution we have is to work proactively. An essential first move, alongside dramatically reducing global CO2 emissions, would be to recognise the climate crisis as a health crisis around the world, and act accordingly.

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Featured image: Globe temperature from 1850 to 2019 by Professor Ed Hawkins.