In an interview with Malaria No More, Tzu-Tung Chen “Sassa”, a doctoral student at the University of Gothenburg, discusses her recent thesis entitled, “Climate-associated human health effects: Lessons from pre-industrial Nordic countries.” In her research, Chen examined the impact of climate change on human health by analyzing church records and historical weather data between 1749 and 1859 to look at climate-associated impacts on malaria and mortality in the Nordic region. Her research concluded that the risk of dying from malaria was higher if the previous summer was a hot one – and that climate had a clear impact on both malaria transmission and mortality in Denmark, Sweden, and Finland.
Your new thesis focuses on malaria and climate; can you tell us about it and what it tells us about the impact of climate change on human health?
CHEN: I'm originally from Taiwan, but in Sweden my work focuses on malaria and health in Nordic countries, especially from Denmark, Sweden, and Finland. Malaria was prevalent in the Nordic countries up until the start of the 20th century. It is estimated that about 1–2 per cent of all deaths were caused by the mosquito-borne virus, often called ‘chills’ in church registers. We looked at historical malaria cases and deaths, and how climate infected malaria incidence. We found that a warm summer often led to more malaria cases in the Nordic countries, especially the preceding summer. So, when there is a warm summer, it's likely we will have more malaria cases in the next year, meaning there is also a risk of insect-borne diseases returning to areas from which they were previously eradicated.
Did your findings surprise you?
CHEN: We were surprised that precipitation wasn’t as significant a factor as temperature. Temperature is most important when it comes to regulating malaria mosquito population, in most cases. A warm summer in the previous year allowed more malaria-infected mosquitoes to hatch, which then started to bite people the following year.
Given the link you show between hot summers and the risks of malaria rising the following year, what does that tell us, if anything, about 2024 given this year was our hottest on record?
CHEN: I think the future implication is…that we know temperature, especially in the warmer climates, really affects mosquitoes’ populations, not only the past, but the future. Because of the past, we know temperatures, especially during the summer, will impact mosquitoes. We will probably see more cases - not of malaria - but from other mosquito borne diseases like dengue fever and the Zika virus. We are already seeing dengue fever, Zika virus and West Nile virus moving further north in Europe as the tiger mosquitoes that carry these diseases become established.
What compelled you to examine this topic of malaria and climate?
CHEN: We were trying to find out what health impacts are strongly associated with climate change, especially warming, to improve resilience in the future. We looked at different diseases, like tick borne disease, malaria or mosquito borne diseases. The thing is that other kinds of climate sensitive diseases don't have the same kind of long-term records as malaria. Although it's not a big concern now in the Nordic countries, it’s a good tool that we have. We take what we have. The church records enable you to get more details like the spatial patterns or the hotspot of the malaria cases.
As the climate grows warmer and the risks increase of insect-borne diseases returning to areas previously eradicated, what does your research conclude about improving resilience in the future?
CHEN: Building climate resilience is important in a changing climate. It’s better to prepare than not be prepared. I’m also looking at how when sea levels rise that this affects the coastal area. We know that some of the malaria mosquitoes prefer brackish water. In the future, many coastal areas could be flooded or invaded by water. Rising sea levels are very strongly related to climate change. This will be something that we need to pay attention to, particularly areas that could be quite vulnerable.