Climate change is an invisible killer. A family that lived in a hill station in India, an area known for its colder climate, took their sick child to the hospital. Nobody thought of dengue until a diagnosis confirmed it. Warmer temperatures in India and elsewhere make conditions more favourable for mosquitoes.
"Nobody is immune [to climate change] whether you are poor or rich," said Dr Naveen Rao, senior vice-president of the Health Initiative at The Rockefeller Foundation, of his cousin's child in an interview at the regional office in Bangkok. "Climate change affects everybody."
In India, dengue simmered and then broke out in 1996. It has increased dramatically over the past decade. A study published in Nature last year found that climate change has worsened infectious diseases. Rising temperatures are making environments more suitable for vectors, including mosquitoes which can spread dengue and malaria.
Dr Rao joined the Prince Mahidol Award Conference on the theme of climate change, biodiversity loss and pollution last month. After a 25-year career with Merck, he joined the Rockefeller Foundation where he is working to ensure equitable access to Covid-19 tests and vaccines, science-based tools, and data for the prevention of future outbreaks.
Founded by American industrialist and philanthropist John D. Rockefeller, the organisation has worked in Asia for more than a century. Its presence in Thailand dates back to the eradication of hookworm in 1914 and the development of the health ministry. On a larger scale, the Rockefeller Foundation helps countries around the world tackle public health issues.
Speaking on the impact of climate change on human health, Dr Rao said floods, swamps or any source of stagnant water, including a container at home, can provide a breeding ground for mosquitoes. For example, when they bite those infected with dengue, they pick up the virus and spread it to other people, which usually takes around 10 days.
"But in a warmer climate, the virus can duplicate faster [in mosquitoes] in 2-3 days," he said.
According to the World Health Organization, 390 million dengue infections occur every year, 96 million of which have clinical manifestations. A study published in Nature in 2019 predicted that dengue will impact over 6.1 billion people or 60% of the world's population by 2080.
Still, there is no warning system for climate-sensitive infectious diseases.
Dr Rao stressed the need for unified data collection to monitor and prevent future outbreaks. Once basic rules are put in place to ensure data governance, the system will work by enabling users to share and access real-time on-ground information. It will alert those involved to any outbreak and assess its gravity, for example diarrhoea.
"People aren't eager to share bad health data," he said. "It is a utopia in that everybody shares what everybody does. We need to go there because we are all sinking. Climate change is not affecting only one country. More spillovers, more pandemics and more infections from animals to humans. All of it is happening."
Dr Rao said data collection requires an investment in basic infrastructure. In his view, Thailand is a good example of a resilient public health system, connectivity and social capital. In the face of Covid-19, people were more willing to follow measures like wearing face masks, social distancing and contact tracing.
"When the pandemic hit, America was one of the worst in terms of community trust. There was no contact tracing in America because nobody wanted to give information. There was no community trust or community health workers. America did not do well," he said. "[Thai] culture is more about community, not about me. I am not saying it is good or bad. It is different."
Dr Rao said no matter how important data is, it takes political will to act on it.
Recalling his personal experience, he said authorities treated infectious diseases in a medical way because they were unaware of the social determinants of health. But even nowadays, there is still climate change denial.
"We have so much [research] on climate change over the past 20 years. I don't know if you have seen the photo of the polar bear on a small piece of ice. If you see that photo, I don't know if you need any more data. But there are people who deny it. Data by itself is not going to do it. You need leadership and political will," he said.
Last year, the UN confirmed that there is "no credible pathway" to limit global warming to the threshold of 1.5°C, which will have dangerous impacts on people all over the world. Policies currently in place point to a 2.8°C temperature rise by the end of the century. Implementation of pledges will only reduce this to a 2.4-2.6°C.
"What kind of life your grandchild will enjoy is based on what you are doing today," he added.
Summary of the impact of climate change on dengue Climate hazards exacerbate the impact of dengue fever, according to the Rockefeller Foundation.
In terms of biology, higher temperatures can affect the reproductive capacity of mosquitoes, stimulating egg hatching and accelerating the growth of larvae, thus decreasing the time to maturity. At higher temperatures, mosquitoes bite more frequently. Heat enhances dengue virus replication inside mosquito hosts.
Climate change, excess precipitation, storms, flooding and rising sea level can increase the number of mosquitoes by providing the stagnant pool of water they need to reproduce. Meanwhile, drought can increase their population because people save water in containers that can provide a breeding ground for larvae.
Urbanisation or deforestation can increase the risk of dengue fever by initiating contact with vectors that had been more isolated from inhabited areas.
As land becomes unliveable or unfarmable, people may have to migrate into new areas and carry diseases, including dengue, with them, or they may be newly exposed to endemic diseases to which they have little resistance.
