Network analysis of cattle movements in Chile: Implications for pathogen spread and control.

Livestock movement between herds is one of the main routes for a pathogen to spread between herds. Understanding the contact structure, patterns and importance of specific individuals and classes can help assess dissemination risk, control, and surveillance measures. In this study, the cattle herd's contact structure in southern Chile was characterized based on the study of movement within one of the most important geographical regions for livestock production. Using Social Network Analysis, network measures of centrality, network cohesion and contact chains were estimated to identify essential features that can influence disease transmission among premises. Static and disaggregated by season networks were built for the entire set of nodes and for the Los Rios region animal flow only. For all networks, it was found that most nodes had a few movements; meanwhile, a small number of them were highly connected. Livestock markets have a powerful influence over the networks, being the most connected and central nodes, appearing as candidates for surveillance because of their possible role as super spreaders. Nodes attributes were associated with the likelihood of having high contact chains measures, such as herd class, location, and presence of markets anywhere on the contact chain. This work is the first deep analysis in livestock flows in Chile and shows the importance of animal movement data interpretation to assess pathogen risk spread in the country.

Bovine Viral Diarrhea Virus within and herd prevalence on pasture-based dairy systems, in southern Chile dairy farms.

Bovine Viral Diarrhea (BVD) is a ubiquitous endemic disease in most bovine populations that causes a negative economic impact on cattle production systems. However, true herd and individual prevalence in Chile have not been estimated based on statistical and epidemiological considerations and uncertainty regarding the infection's extension at animal and herd levels. In addition, the risk factors that can influence how the infection has spread among the cattle premises have not been assessed yet. Therefore, the study aimed to estimate true herd and animal prevalence of active BVDV infection in pasture-based dairy herds and to evaluate risk factors potentially associated with the status of herds and the within-herd prevalence, using a Bayesian approach. A cross-sectional study was performed over a random stratified (proportional to herd size) sample of one-hundred and fifty dairy herds selected in Chile's two leading dairy regions (Region de Los Ríos and Region de Los Lagos). We obtained 12.311 blood samples from lactating cows, but 4.998 randomly selected samples were processed due to budget constraints. For estimating BVDV Herd Prevalence (HP), a herd was considered infected if at least one positive animal to Ag-ELISA was found. In addition, a survey was completed on each farm, aiming to collect information to assess the influence of some variables over the state of the herds; both estimations were obtained using a Bayesian approach. True herd prevalence and true individual prevalence of BVDV active infection were estimated at 77 % and 3.5 % respectively, no significant differences were found between characteristics like herd size, location, vaccination, etc. Open herds and herds that mix herd categories are more likely to have higher BVDV prevalence.