A planet supporting life

Published on August 1st, 2013 | by Emily Corbett

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Statistical models for wildlife contact networks – confronting theory with data

By Shrupa Shah, RMIT University

This student took part in the 2012/13 AMSI Vacation Research Scholarship program. For more information on this years program please click here

blog - Shah1

Mathematical models for infectious diseases typically use contact rates (e.g. the number of other people a person encounters per day) as one of their main elements in predicting the outcomes of an epidemic. The aim of my project is to investigate the importance of spatial constraints and individual heterogeneity on the rate of contact of wildlife using field voles (Microtus agrestis) as a case study. By spatial constraints, I mean the importance that spatial distance plays in the rate of contact. Furthermore by individual heterogeneity, I mean the importance of characteristics such as mass and sex in determining the rate of contact.

We intuitively know that the further apart two individuals/voles are from each other, the harder it would be for a pathogen to spread. But how far is far? Incorporating these spatial constraints into the rate of contact models would help us investigate this. Studying characteristics such as mass and sex would help us investigate the features of dominant hubs in the network.

I studied the contact networks of field voles to better understand the characteristics of dominant hubs. Contact networks were formed such that each vole trapped during a trapping session represented a node and since contacts were not directly observed they were inferred from trap sharing. In addition to that, each vole was assigned an x-coordinate and y-coordinate to help calculate the Euclidean distance between two voles. We used characteristics such as mass and sex to categorise the voles into three groups, Big Males, Females and Small Males, the last having mass less than 25 grams.

We found significant evidence that the Big Males formed the dominant hubs in the network. If we can target these dominant hubs for vaccination/ removal then an epidemic might be brought under control faster or an outbreak prevented.

1 – http://www.warrenphotographic.co.uk/photography/bigs/26631-Field-Vole-white-background.jpg

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