Figure 2
A schematic illustration of backward- and forward contact-tracing, and the network measures degree and contact chains . The encircled farm, P, represents the starting point for the contact tracing, in EpiContactTrace defined as the root. The arrows represent livestock movements, where t represents the point in time when the movement occurred. The left side shows ingoing contacts to P (backward tracing) and the right side outgoing contacts from P (forward tracing). The in-degree, i.e. direct ingoing contacts will be 3 (K, N and O) and correspondingly the out-degree will be 3 (Q, T and O). Since the same farm can be both among ingoing and outgoing contacts, this is exemplified with farm O. The measures ingoing and outgoing contact chain takes temporal aspect into account, i.e. the order in which the movements occurred. Given that t1 and t2 occurred before t3 and moreover that t4 occurred before t5 and that t5 occurred before t6 or t7, the ingoing contact chain will be 7. Given that ta occurred before tb and tc and moreover that td occurred before te or tf, and that te or tf occurred before tg, the outgoing contact chain will be 7. The movement arrow with time tx illustrates the case where the same farm is included in different parts of the chain creating a cross-contact. Although appearing in different parts of the chain, a farm will only be counted once when indicating the measure contact chain.