Understanding monkey to human malaria transmission
In this blog post, Paddy Brock discusses his co-authored review ‘Plasmodium knowlesi transmission: integrating quantitative approaches from epidemiology and ecology to understand malaria as a zoonosis’, which is the Parasitology article of the month. In it he reflects on how quantitative models are not just a means to understand disease transmission, but can also provide a platform for researchers from across disciplines to work together effectively.
Plasmodium knowlesi, a form of malaria that usually infects macaques and that had received relatively little research attention until 12 years ago, is now considered a threat to human health in South East Asia. In the 1930s P. knowlesi was traded by doctors experimenting with malaria-induced fever as a cure for syphilis, and in the 1960s an American caught it after a stint of night-time activity in the forests of Peninsula Malaysia. At the time it was assumed that this single instance of transmission from monkeys to humans was anomalous. However, in 2004 several malaria cases in Malaysian Borneo were found to be caused by zoonotic P. knowlesi rather than human P. malariae. As more sensitive tests were introduced, more and more human P. knowlesi cases were diagnosed, many of them severe and some of them fatal.
In our review we discuss research on P. knowlesi in the context of understanding its transmission, with a view to best preventing human infection. We explore whether all human infections are caused by mosquitoes that have been infected by macaques (spillover), or whether mosquitoes might pass infection from human to human. We also consider the relationship between land use change and P. knowlesi risk. Even after accounting for increased awareness of P. knowlesi, the number of cases reported each year appears to be rising, and this is thought to be due to human modification of the environment in which the macaques and mosquitoes that transmit the parasite live.
To unravel the complexities of zoonotic P. knowlesi transmission, future research will need to draw on methods from both epidemiology and ecology, both of which use mathematical models of systems as research tools. Mathematical models abstract networks of interactions and the mechanisms that define them so that phenomena – such as zoonotic transmission – can be studied in a whole-system context. This holistic perspective means that models also act as natural frameworks for the integration of varied data from multiple sources, and provide focus for the collaborative exploration of ideas, which can generate new insight and make transdisciplinary communication more effective.
Over the last two years, I’ve been taking part in a science-art project (Silent Signal) that has made me think about the value of models as frameworks for intellectual exchange. Silent Signal paired scientists with artists, and in response to our conversations, the artists boredomresearch created an artwork (AfterGlow), a generative digital animation that explores malaria transmission aesthetically. At the beginning, our perspectives and motivations were so different it seemed we would never see eye-to-eye about one another’s work. However, the model (the algorithm that generates the live artwork, which superficially resembles the mathematical models we use for our research on P. knowlesi) proved to be a valuable central plank for our discussions, and gave us hope that it was worth continuing to bang our heads together! And it was. The experience helped me shift my perspective on scientific disciplines away from islands between which to build (interdisciplinary) bridges towards a more connected landscape in which walls even at their most formidable are like hedgerows – porous and diverse.
Understanding and interrupting Plasmodium knowlesi transmission is the type of complex problem that would not only benefit from transdisciplinary integration (across primatology, clinical science, entomology, geography and social science) but that requires it, which is one of the points we make in our review. A proposed route to this kind of integration is to nurture the career development of T-shaped scientists, who are experts in their field and have the skills to work across many others. What working with boredomresearch on Silent Signal taught me, is that the transition to constructive dialogue need not take the length of a career. With our models as a central focus for discussion, the desire to achieve mutual understanding as our shared mission, and the support of progressive institutions, we made the journey to T during the course of a single project. If models can catalyse this process across subjects as different as contemporary art and malaria research, perhaps they could be used more widely in science to facilitate constructive transdisciplinary dialogue.
Paddy Brock is a researcher at the Institute of Biodiversity Animal Health and Comparative Medicine at the University of Glasgow. This research was funded by the Medical Research Council, Natural Environment Research Council, Economic and Social Research Council, and Biotechnology and Biosciences Research Council through the Environmental and Social Ecology of Human Infectious Diseases Initiative (grant number G1100796). Silent Signal was produced by Animate Projects with support from a Wellcome Trust Large Arts Award.