The index case is not enough: Variation among individuals, groups and social networks modify bacterial transmission dynamics

5 years ago

The index case is not enough: Variation among individuals, groups and social networks modify bacterial transmission dynamics

Krishna S. Kothamasu, Carl N. Keiser, Jonathan N. Pruitt, Noa Pinter-Wollman, Michael J. Ziemba

The traits of the index case of an infectious disease outbreak, and the circumstances for their aetiology, potentially influence the trajectory of transmission dynamics. However, these dynamics likely also depend on the traits of the individuals with whom the index case interacts. We used the social spider Stegodyphus dumicola to test how the traits of the index case, group phenotypic composition and group size interact to facilitate the transmission of a GFP-labelled cuticular bacterium. We also compared bacterial transmission across experimentally generated “daisy-chain” vs. “star” networks of social interactions. Finally, we compared social network structure across groups of different sizes. Groups of 10 spiders experienced more bacterial transmission events compared to groups of 30 spiders, regardless of groups’ behavioural composition. Groups containing only one bold spider experienced the lowest levels of bacterial transmission regardless of group size. We found no evidence for the traits of the index case influencing any transmission dynamics. In a second experiment, bacteria were transmitted to more individuals in experimentally induced star networks than in daisy-chains, on which transmission never exceeded three steps. In both experimental network types, transmission success depended jointly on the behavioural traits of the interacting individuals; however, the behavioural traits of the index case were only important for transmission on star networks. Larger social groups exhibited lower interaction density (i.e. had a low ratio of observed to possible connections) and were more modular, i.e. they had more connections between nodes within a subgroup and fewer connections across subgroups. Thus, larger groups may restrict transmission by forming fewer interactions and by isolating subgroups that interacted with the index case. These findings suggest that accounting for the traits of single exposed hosts has less power in predicting transmission dynamics compared to the larger scale factors of the social groups in which they reside. Factors like group size and phenotypic composition appear to alter social interaction patterns, which leads to differential transmission of microbes. The authors disentangle the effects of host traits, social context and social network structure on bacterial transmission dynamics. Using a fluorescence-tagged cuticular bacterium, they show that group size and phenotypic composition both influence bacterial transmission, and that transmission dynamics may be a product of the structure of group interaction networks.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1111/1365-2656.12729