Abstract
The objectives of this research were to describe the contact structure of transportation vehicles and swine facilities in an Ontario swine production system, and to assess their potential contribution to possible disease transmission over different time periods. A years’ worth of data (2015) was obtained from a large swine production and data management company located in Ontario, Canada. There was a total of 155 different transportation vehicles, and 220 different farms within the study population. Two-mode networks were constructed for 1-,3-, and 7-day time periods over the entire year and were analyzed. Trends in the size of the maximum weak component and outgoing contact chain over discrete time periods were investigated using linear regression. Additionally, the number of different types of facilities with betweenness >0 and in/out degree>0 were analyzed using Poisson regression. Maximum weekly outgoing contact chain (MOCCw) contained between 2.1% and 7.1% of the study population. This suggests a potential maximum of disease spread within this population if the disease was detected within one week. Frequency of node types within MOCCw showed considerable variability; although nursery sites were relatively most frequent. The regression analysis of several node and network level statistics indicated a potential peak time of connectivity during the summer months and warrants further confirmation and investigation. The inclusion of transportation vehicles contributed to the linear increase in the maximum weekly weak component (MWCw) size over time. This finding in combination with constant population dynamics, may have been driven by the differential utilization of trucks over time. Despite known limitations of maximum weak components as an estimator of possible outbreaks, this finding suggests that transportation vehicles should be included, when possible and relevant, in the evaluation of contacts between farms.
Highlights
Network analysis as a tool for epidemiologists has been around at least since the 1980s [1]
Company External was used to describe entities that, over a period of the entire year, served as source of animals for nodes within the production system, but could be destination for animals from nodes within the production system [4]. This resulted in the network that consisted of 375 unique facilities, in which truck license plates were added to the swine production related sites
2 nodes were classified as Company Internal (CI), 9 nodes as CE and 4 nodes as Company Export (CEX) which all together accounted for ~4% of the facilities
Summary
Network analysis as a tool for epidemiologists has been around at least since the 1980s [1] It has become a frequently utilized approach within veterinary epidemiology to help expand our understanding of disease transmission for production animal research [2,3,4,5,6,7,8]. Knowledge about the movement of animals is essential for understanding the potential for diseases to spread [9]. In swine populations, this movement is frequent in areas where strict age segregation and external sources of replacement animals are common practices. Transportation vehicles involved in animal movement can provide a means for disease spread
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