Cattle transport network predicts endemic and epidemic foot-and-mouth disease risk on farms in Turkey

Abstract

The structure of contact networks affects the likelihood of disease spread at the population scale and the risk of infection at any given node. Though this has been well characterized for both theoretical and empirical networks for the spread of epidemics on completely susceptible networks, the long-term impact of network structure on risk of infection with an endemic pathogen, where nodes can be infected more than once, has been less well characterized. Here, we analyze detailed records of the transportation of cattle among farms in Turkey to characterize the global and local attributes of the directed—weighted shipments network between 2007-2012. We then study the correlations between network properties and the likelihood of infection with, or exposure to, foot-and-mouth disease (FMD) over the same time period using recorded outbreaks. The shipments network shows a complex combination of features (local and global) that have not been previously reported in other networks of shipments; i.e. small-worldness, scale-freeness, modular structure, among others. We find that nodes that were either infected or at high risk of infection with FMD (within one link from an infected farm) had disproportionately higher degree, were more central (eigenvector centrality and coreness), and were more likely to be net recipients of shipments compared to those that were always more than 2 links away from an infected farm. High in-degree (i.e. many shipments received) was the best univariate predictor of infection. Low in-coreness (i.e. peripheral nodes) was the best univariate predictor of nodes always more than 2 links away from an infected farm. These results are robust across the three different serotypes of FMD observed in Turkey and during periods of low-endemic prevalence and high-prevalence outbreaks.

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“…a holding or a district, with other epidemiological units which have a similar attribute, e.g. number of trade links (degree assortativity) or location (district assortativity and federal state assortativity) 96,97 .…”

“…A shorter diameter means that the number of generations for a disease to spread throughout the network is reduced. 6,97 Global clustering coefficient (CC) Fraction of closed triplets, i.e. three nodes linked to each other and forming a closed triangle, among all possible triplets.…”

Assessing the impact of structural modifications in the construction of surveillance network for transboundary animal diseases: the role of backbone and sentinel nodes

“…The importance of eigenvalue centrality increased with an increase in transmission probability and became the most crucial factor for ρ = 0.75. As defined in (27), the eigenvalue centrality indicates the node's importance, which is expected since structural properties take the lead for ρ close to 1 and consistently maintain a high value across all transmission probabilities, indicating a robust influence of incoming connections.…”

Network analysis of pig movement data as an epidemiological tool: an Austrian case study

“…a holding or a district, with other epidemiological units which have a similar attribute, e.g. number of trade links (degree assortativity) or location (district assortativity and federal state assortativity) 99 , 100 . Average path length The average number of steps along the shortest paths for all possible pairs of nodes.…”

“… Longest geodesic distance between any pair of holdings in the network. A shorter diameter means that the number of generations for a disease to spread throughout the network is reduced 6 , 100 . Global clustering coefficient (CC) Fraction of closed triplets, i.e.…”