Spatio-temporal network analysis of pig trade to inform the design of risk-based disease surveillance.

Network analysis is a powerful tool to describe, estimate, and predict the role of pig trade in the spread of pathogens and generate essential patterns that can be used to understand, prevent, and mitigate possible outbreaks. This study aimed to describe the network between premises such as production herds, slaughterhouses, and traders of pig movements and identify heterogeneities in the connectivity of premises in the state of Santa Catarina, Brazil, using social network analysis (SNA). We used static and temporal network approaches to describe pig trade in the state by quantifying network attributes using SNA parameters, such as causal fidelity, loyalty, the proportion of node-loyalty, resilience of outgoing contact chains, and communities. Two indexes were implemented, the first one is a normalized index based on SNA-farm level measures and other index-based SNA-farm level measures considering the swineherd population size from all premises, both indexes were summarized by a municipality to target and rank surveillance activities. Within Santa Catarina, the southwest region played a key role in that 80 % of trade was concentrated in this region, and thus acted as a hub in the network. Besides, nine communities were found. The results also showed that premises were highly connected in the static network, with the network exhibiting low levels of fragmentation and loyalty. Also, just 11 % of the paths in the static network existed in the temporal network which accounted for the order in which edges occurred. Therefore, the use of time-respecting-paths was essential to not overestimate potential transmission pathways and outbreak sizes. Compared to static networks, the application of temporal network approaches was more suitable to capture the dynamics of pig trade and should be used to inform the design of riskbased disease surveillance.

Brucellosis in working equines of cattle farms from Minas Gerais State, Brazil.

The present survey aimed at estimating the seroprevalence of brucellosis in working equines of cattle farms from Minas Gerais State, Brazil, and investigating risk factors associated with the infection. Serum samples from 6439 animals, including 5292 horses, 1037 mules and 110 donkeys, were collected from 1936 herds, between September 2003 and March 2004, in 848 municipalities from the state of Minas Gerais, Brazil. The prevalence of antibodies against smooth Brucella spp. found in equines from Minas Gerais State was 1.37% (95% CI: 0.97-1.78), resulting in a prevalence of herds with infected animals of 4.28% (95% CI: 4.21-4.36). There were differences between regions but these were not of major epidemiological relevance nor were most of them statistically significant, given the considerable overlap of confidence intervals. Nevertheless, the point estimates suggest that the three northeastern regions have slightly higher prevalence than the rest of the state, both at the herd and animal levels. No association of Brucella spp. seropositivity with sex, age or host was observed. In conclusion, the present study showed a low but widespread prevalence of antibodies against smooth Brucella in equines kept in cattle farms in Minas Gerais, a state where bovine brucellosis is also widespread albeit with low prevalence.