Metapopulation dynamics of infectious diseases
Grenfell, Bryan, and John Harwood. “(Meta) population dynamics of infectious diseases.” Trends in ecology & evolution 12, no. 10 (1997): 395-399.
At the time of this publication, the idea that metapopulation theory could apply to epidemiological systems was new. Ecologists made substantial advances in the theory of meta-populations but many of their theories lacked empirical validation. The gap in empirical validation was due to the need for high quality spatio-temporal data in systems where the underlying biology was well enough understood to produce metapopulation models. Whereas ecological data was seldom long enough or of high enough resolution, epidemiological data was longer and of high resolution due to required disease reporting, and additional variables could be deduced such as fade-outs and importations. Additionally, parallel information pertaining to demographics was often available. Due to these reasons, Grenfell & Harwood suggested that data on notifiable childhood infections were suitable for meta-population analysis.
The authors noted that metapopulation ecology and epidemiology have much in common. In the terms of metapopulation dynamics, susceptible hosts represent available ‘patch’ resources. The presence, absence, and history of infection determines if colonization can occur. If the density of susceptible hosts is high enough, the number of infected individuals can increase exponentially following colonization. As the epidemic progresses, the available patch resources are depleted and the density of infected individuals begins to decrease. Until there is enough build up of susceptible individuals through births, the system resembles a classic metapopulation. The Mean Viable Population (i.e., the population size necessary to survive a finite period with a given probably) is similar to the Critical Community Size (i.e., the population size below which a pathogen will die out) in epidemiology. Because of these similarities, and natural vaccination experiments, Grenfell & Harwood correctly predicted that synthesizing ecological and epidemiological approaches would be a fruitful area of research. They ended the paper by correctly forecasting the study of phylodynamics; a newer field which links genetics to population biology and often aims to describe movement between areas. The idea of linking scales of biological organization was present throughout this paper. Overall, it was interesting to read one of the first papers to bridge the connection between metapopulation ecology and epidemiology.