Illustration of Different Disease Transmission Routes in a Pig Trade Network by Monopartite and Bipartite Representation

Abstract

Besides the direct transport of animals, also indirect transmission routes, e.g., contact via contaminated vehicles, have to be considered. In this study, the transmission routes of a German pig trade network were illustrated as a monopartite animal movements network and two bipartite networks including information of the transport company and the feed producer which were projected on farm level (n = 866) to enable a comparison. The networks were investigated with the help of network analysis and formed the basis for epidemiological models to evaluate the impact of different transmission routes on network structure as well as on potential epidemic sizes. The number of edges increased immensely from the monopartite animal movements network to both projected networks. The median centrality parameters revealed clear differences between the three representations. Furthermore, moderate correlation coefficients ranging from 0.55 to 0.68 between the centrality values of the animal movements network and the projected transportation network were obtained. The epidemiological models revealed significantly more infected farms for both projected networks (70% to 100%) compared to the animal movements network (1%). The inclusion of indirect transmission routes had an immense impact on the outcome of centrality parameters as well as on the results of the epidemiological models.

Modelling and assessing additional transmission routes for porcine reproductive and respiratory syndrome virus: vehicle movements and feed ingredients

“…A recent study developed a new mathematical model to reconstruct the between-farm PRRSV dynamics, revealed the role of between-farm pig movements, indirect contacts by farm-to-farm proximity, and the continued circulation of PRRSV within infected sites (re-break) (Galvis et al, 2021). Despite the promising results, the study did not fully consider indirect contacts formed by the between-farm transportation vehicles networks, which has been previously described as one the major modes of the between-farm transmission of disease in swine (Büttner and Krieter, 2020; Porphyre et al, 2020; Niederwerder, 2021), and also in other systems such as cattle (Yang et al, 2020).…”

“…Detailed data about the flux of transportation vehicles coming in and out premises can be difficult to obtain, which indeed explain lack of mathematical models considering this transmission pathway (Bernini et al, 2019; EFSA Panel on Animal Health and Welfare (AHAW) et al, 2021). Yet, previous studies have approached indirect transmission by transportation vehicles, such as the studies by Thakur et al, 2015 and Wiltshire, 2018, using probabilities to define indirect contact between farms (Thakur, Sanchez et al, 2015; Wiltshire, 2018), or the study by Buttner, 2020 that used observed truck movements between pig farms in Germany (Büttner and Krieter, 2020). The networks formed by transportation vehicles have been also described earlier as potential transmission routes of PRRSV (Dee et al, 2002; Dee et al, 2004; Pitkin et al, 2009; Thakur, Sanchez et al, 2015).…”

“…On the other hand, dry condition and or low pH between5 and 7 (Benfield et al, 1992), and iodine, quaternary ammonium compounds or chlorine used in vehicle disinfection were successful in inactivating PRRSV (Shirai et al, 2000). Thus, if the environmental conditions favor PRRSV survivability, under a poor vehicle disinfection scenario and highly connected vehicle networks (Büttner and Krieter, 2020), it has the potential to propagate pathogens to a large number of farms.…”

“…Despite the promising results, the study did not fully consider indirect contacts through between-farm transportation vehicles (e.g. vehicles transporting pigs, feed or farm personnel) contact networks, which has been previously described as one of the major modes of between-farm transmission of diseases in swine (Büttner and Krieter, 2020; Porphyre et al, 2020; Niederwerder, 2021), such as PRRS (Dee et al, 2002, 2004; Pitkin et al, 2009; Thakur, Sanchez et al, 2015) and African swine fever (ASF) (Gao et al, 2021; Gebhardt et al, 2021).…”

“…In addition, dry conditions, low pH ranging between 5 and 7 (Benfield et al, 1992), iodine, quaternary ammonium or chlorine compounds used in vehicle disinfection were successful in inactivating PRRSV (Shirai et al, 2000). Thus, if environmental conditions favor PRRSV survivability and the vehicles are poorly cleaned and disinfected, the potential for pathogens to disseminate within highly connected networks could indeed play a major role in disease spread (Büttner and Krieter, 2020; Gebhardt et al, 2021).…”