Understanding patient mobility patterns to tackle dengue transmission
The mosquito species that can transmit dengue tend to remain close to their breeding sites and have low mobility - comparatively, the impact of human mobility in the transmission of this disease is substantial, in particular given that these mosquitoes are prone to establishing themselves in densely populated urban areas. In dengue patients, the symptoms of the illness have a strong impact on the mobility choices of infectious individuals. Recent research has looked at the daily human mobility patterns of dengue patients in Iquitos, Peru, to improve the understanding of the complex relationship between symptom severity, infectiousness, and human mobility in order to improve surveillance strategies. In this Infectious Thoughts interview, we speak to Dr. Gonzalo Vazquez Prokopec, Associate Professor in the Department of Environmental Sciences at Emory University, about the methodology of this approach, the challenges posed by asymptomatic dengue cases and the opportunities to improve disease control offered by this type of approach.
Your research is one of the few to collect and analyze human mobility data in order to better understand disease transmission patterns - what were your reasons for undertaking this type of analysis and why did you focus on dengue fever?
We’ve been researching the impact of human mobility on dengue exposure for about 10 years. Previous research has shown that daytime mobility influences where people may get exposed to dengue-infected mosquitoes. What’s relevant in this study is that we are now looking at how disease-driven mobility change may influence where viremic individuals may be spreading the virus next. Our primary goal, thanks to funding from NIH, was to understand the association between dengue illness and human mobility throughout the period of symptomatic illness.
What were the main differences in movement and visits of individuals who contracted dengue fever, based on the interviews of your cohort of dengue patients?
People infected with dengue stopped or significantly reduced the number of locations they visited during the illness period, with such reduction being more marked in the first 3 days of illness. Because they did not move much, they spent most of that daytime at home. As such, our study points to the relevance of the home environment for onwards transmission, for those individuals with dengue illness.
How can this improve disease surveillance strategies and which policy recommendations have come from your approach? What is the impact of asymptomatic cases?
Understanding how dengue viruses are transmitted is strongly dependent on our understanding of how symptomatic and asymptomatic carriers contribute to transmission. Our study shows that, for symptomatic individuals, the home environment may be an important place for onwards transmission, if Aedes aegypti mosquitoes are found there.
Conversely, we can argue that asymptomatic individuals do not change their mobility behavior due to illness. As such, asymptomatic carriers may have a larger role in spreading the virus to locations other than their house in comparison to symptomatic dengue infections.
Current vector control interventions primarily focus on reactive vector control to reported symptomatic cases. We see a lot of value in our findings because they may indicate that responding to symptomatic reported cases may miss a significant proportion of transmission driven by those who do not change their mobility and are able to infect a large number of Aedes aegypti mosquitoes.
In which other ways would you be interested to further develop your approach? Can this be applied to different settings and diseases? Are there further products or partnerships which you would like to see developed in order to facilitate your next steps?
There is a desperate need to better understand how disease influences transmission dynamics. Confirming our findings in our settings would be the first step.
Further, this knowledge proposes a change in how trials evaluating epidemiological endpoints are designed. We need to account for behavior (and disease-driven mobility) in order to understand the impact of vector control interventions.
Dengue illness impacts daily human mobility patterns in Iquitos, Peru
Kathryn L. Schaber, Valerie A. Paz-Soldan, Amy C. Morrison, William H. D. Elson, Alan L. Rothman, Christopher N. Mores, Helvio Astete-Vega, Thomas W. Scott, Lance A. Waller, Uriel Kitron, John P. Elder, Christopher M. Barker, T. Alex Perkins, Gonzalo M. Vazquez-Prokopec
Published: September 23, 2019