Network analysis of host–virus communities in bats and rodents reveals determinants of cross-species transmission

Luis, Angela D.; O'Shea, Thomas J.; Hayman, David T. S.; Wood, James L. N.; Cunningham, Andrew A.; Gilbert, Amy T.; Mills, James N.; Webb, Colleen T.

The most important host characteristics associated with degree in bats were gregariousness and sympatry. These characteristics have been hypothesised as important mechanisms for viral maintenance and spread (Calisher et al. 2006; Luis et al. 2013 )bat species with distributions that overlap with a greater number of other bat species, and particularly those which are gregarious, will have greater interspecific contacts and chance for cross-species transmission. At some roosting sites, bat densities can be as high as 3000 bats per square metre, and some roosts house diverse assemblages of species (Constantine 1967; Kunz 1982) . High densities can lead to high contact rates, facilitating pathogen transmission and persistence. These dense roosting sites are often caves, therefore we had hypothesised that propensity to roost in caves would be an important predictor of viral sharing in bats. However, colony size (gregariousness) was more important than where the colony roosts. Large colony sizes do not occur on the same scale in rodents and may have led to the higher mean degree and connectance in bats compared to rodents. Species with high betweenness might not have or share the most viruses, but could play a key role in disseminating viruses because they can connect disparate regions of the network. Migration was the most important host trait associated with betweenness in bats. Long-distance animal movement has been hypothesised to enhance geographic spread of infectious disease, however, evidence in most cases is lacking (Altizer et al. 2011 ). In the bat network, many of the shortest network paths went through regional migrants (moving 100-500 km annually), which were more important than long-distance migrants (> 500 km). This is consistent with the idea of 'migratory culling' (Bradley & Altizer 2005) in which the physiological stress of long-distance migration can increase mortality of infected individuals.