Tiem van der Deure: Predicting vector-borne disease risk under climate change – Impacts across Africa and Europe

BACKGROUND
Climate change is an accelerating threat to human well-being. Changes in temperature and rainfall patterns are changing the conditions for disease transmission. Diseases that are transmitted by vectors such as mosquitoes or snails are particularly affected by climate change, for instance when vectors can spread to new areas, or their biting patterns or population size changes.

PURPOSE
In my PhD project, I investigated the effects of climate change on three important vector-borne diseases: malaria, schistosomiasis, and fascioliasis. Malaria is transmitted by mosquitoes and causes over half a million deaths every year. Schistosomiasis is a chronic disease that is caused by a parasite transmitted by snails and affects over 150 million people. Fascioliasis is also caused by a snail-borne parasite, and affects both people and livestock around the world. 

I seek to understand how the risk of these diseases is affected by climate, and how disease risk will change under future climate change. I do so using ecological models, that combine data on where vectors and diseases are found, as well as experimentally measured traits that can tell us what climatic conditions are favorable for these pathogens.

RESULTS
In Chapter I, I used models to predict the future range of six important mosquito vector species of malaria in Africa. These models showed that three of these species will experience more favorable conditions under climate change. This shows species-specific responses to climate change of vector species, and suggests additional measures might be needed in the future to deal with increased suitability. 

In Chapter II, I investigated the schistosomiasis host snail Bulinus truncatus using two different models based either on occurrence records or experimental evidence. Both models showed B. truncatus might expand in Eastern Africa and Southern Europe, increasing risk for schistosomiasis in those regions. In the Sahel region, the models made opposing predictions, showing the uncertainty in climate impacts that comes  from model design.

In chapter III, I developed a risk index for two species of Fasciola liver fluke parasites that cause fascioliasis in both humans and livestock. The risk index was able to reproduce known patterns for both species, with high risk of tropical species F. gigantica in Africa and for the temperature species F. hepatica in Europe. Under climate change, risk for both species is predicted to decrease across most of the range, except for in northern Europe.

In the final chapter, I used abattoir registration of liver fluke in Danish beef cattle to show that wetter and colder summers are associated with increased transmission. This also suggest climate change might result in decreased liver fluke transmission risk in Denmark.

THE FUTURE
Overall, this thesis adds to the growing body of evidence of the impacts of climate change on disease transmission by showing how climate change might reshape the landscape of vector-borne disease risk. It also shows some of the gaps and uncertainties that remain. Different modelling approaches result in diverging predictions for the future, specifically in areas that will be extremely warm, such as the Sahel region. Resolving these conflicts will require careful analysis of modelling techniques and limitations, but also additional data generation.

This work also shows the interconnections between environmental, animal, and human health, which are increasingly recognized. Developing integrated approaches will be crucial to simultaneously safeguarding the health of ecosystems, livestock, and humans. As my work shows, this requires recognizing the importance of disease-transmitting vector species and their species-specific ecology.

As global warming continues to accelerate and is projected to well exceed 2 °C by the end of the century, the redistribution of vector-borne disease risk will affect hundreds of millions of people. While action to reduce greenhouse gas emissions can avert some of these changes, vector control and surveillance programs need to be adapted to deal with changing risk.

FOR MORE INFO: https://www.linkedin.com/posts/tiem-van-der-deure_last-friday-i-defended-my-phd-this-activity-7459978988401319937-rkZ4