Dr. Paaijmans: Recent years have seen a (re)emergence of vector-borne disease in southern Europe

Dr. Krijn Paaijmans won one of the two ISGlobal Emerging Leaders positions and has recently joined CRESIB, ISGlobal's research centre, as an Assistant Research Professor.

Dr. Paaijmans holds a degree in Biology (2002, Wageningen University) and did his Ph.D. studies in Medical Entomology (2008) at the Laboratory of Entomology & the Department of Meteorology and Air Quality at Wageningen University. He has worked on his post-doc at the Department of Entomology and the Center for Infectious Diseases Dynamics at Pennsylvania State University. At CRESIB, he will initiate new research in ecology of vector-borne diseases.

Climate change is one of the big global issues of our time. What does it mean for vector-borne diseases?

Arthropod vectors and the pathogens they carry (such as mosquitoes transmitting malaria and dengue, fleas transmitting plague, and ticks transmitting Lyme disease) are small and ectothermic. This means that the temperature of their direct surroundings influences their behaviour, physiology, and development. Although the dynamics and distribution of vector-borne diseases are expected to be extremely sensitive to climate change, the nature and extent of their response remain highly controversial. This is the result of a poor understanding of the mechanistic link between environmental variables and disease risk. But, in addition, there are several other intrinsic and extrinsic drivers of disease (e.g. rainfall, socio-economics, drug and insecticide resistance, intervention strategies, etc.). The interplay of these intrinsic and extrinsic factors ultimately determines disease risk. So there is not one right answer to this question. It depends on where you are on our planet.

The idea that climate change will bring malaria and other vector-borne diseases to our door turns out to be an extremely controversial one. Is South Europe becoming a "hotspot" for infections typically confined to tropical climates?

Recent years have seen a (re)emergence of vector-borne disease in southern Europe. To give a few examples: autochthonous cases of malaria in Greece (2009) and Spain (2010), of Chikungunya in Italy (2007) and of dengue in Portugal (2012) have been reported. To what extent climate change plays a role here is difficult to tell. It is important to realize that susceptible and competent mosquito vectors have either always been present or have recently established successfully in Europe (e.g. the ‘famous' tiger mosquito, a big nuisance mosquito, but also a potential vector of West Nile, Chikungunya and dengue). So how can climate change affect epidemics? Warmer summers may results in faster mosquito population growth, faster pathogen development, increased biting frequency (increasing transmission potential), etc. Longer periods of suitable temperatures can lead to more mosquito generations per year, and milder winters will benefit mosquito survival. These could all increase the probability that a mosquito will pick up a disease from an imported case and subsequently transmit it to another person.

How is your research related to these issues?

Before we can start predicting the impact of future climates, there is a need to focus on the present and get a better grip on the basic biology and ecology of vectors and pathogens. The main aim of my research is to quantify how climatic conditions influence disease transmission. I combine empirical work (laboratory experiments with mosquitoes and malaria) with theoretical work, thereby focussing on largely ignored, but ecologically relevant environmental parameters. Temperature-based malaria transmission is generally incorporated into epidemiological models using mean monthly temperatures, derived from local weather stations. My research shows that daily temperature fluctuation can substantially alter parasite infection, the rate of parasite development, and the essential elements of mosquito biology, and hence malaria transmission limits and intensity. In addition, standard estimates of environmental temperature derived from local weather stations do not necessarily provide realistic measures of temperatures within actual transmission environments. These and other studies show again and again that greater effort should be directed at determining the climate actually experienced by mosquitoes and parasites in local transmission environments. I hope that my research will improve the accuracy of current epidemiological models.

At present, eradication of malaria still remains beyond our grasp but it is back on the global health agenda as a long-term target. How do you think your research can contribute to this goal?

By better understanding the biology and ecology of mosquitoes and parasites, I hope to gain novel insights into the factors that contribute to the current dynamics and distribution of disease, and how these may change in the future. Although many scientists would argue that the role of climate can be neglected, there is no denying that climate does affect the basic biology of mosquitoes and parasites. Whether it is a main driver of disease risk depends on other factors, as I highlighted above. Climate will be a main driver in poor areas, where factors such as a good health infrastructure and proper interventions are lacking. But climate may soon start to play a more important role again in areas where malaria control is currently successful. Unfortunately, mosquitoes are becoming resistant to insecticides used in bed nets and sprays, and malaria parasites are becoming resistant to front line drugs. Combined with question marks over long-term donor commitment to fund control programmes, accurately quantifying (baseline) disease risk remains a necessity.

Last but not least, what moved you to apply for a position at the Barcelona Institute for Global Health? What do you think you can contribute to this centre and viceversa?

When the job ad was posted, the first thing I did was to visit CRESIB's website. As soon as I saw the organisation matrix, listing all the research ‘programs' and ‘areas', I realised there were many opportunities for collaborations for an entomologist like me. At ISGlobal I hope to continue my current research but also to translate my research to other areas (e.g. neglected tropical diseases such as Chagas), and to initiate new studies (e.g. contribute to ongoing malaria intervention trails by monitoring parasite prevalence in local mosquito populations). In addition, the collaborations between CRESIB and strategic research collaborators abroad open up possibilities to test whether laboratory results can be translated to field situations. And last but not least, setting up a malaria mosquito colony ranks high on my wish list. Apart from enabling myself to do various malaria infection and transmission experiments, I believe that such a mosquito facility can benefit various other projects here at the institute and will open new research avenues. In summary, enough ideas, possibilities and opportunities that will keep me buzzing with excitement for many years to come!