Figure 2.

(a) Framework for capturing transient phase infection dynamics. The movement path of hosts and their infections (intensity/probability represented by darker shading of the arrow being higher intensity/probability) are categorized into three phases: departure, transience and arrival. During transience, infections are lost/reduced through background or disease-induced mortality of infected hosts, or as conditions during transience decrease exposure and/or cause deterioration of infections (i.e. recovery). Mechanisms that drive recovery include: (b–c) movement through habitats unsuitable for infections, which may occur with protozoal infections during monarch butterfly migrations [6] and with tick infections during ranging movements of livestock [41]; (d) enhancement of immune function during periods of movement, which may occur in migratory red knots [42]; and (e) dispersion of hosts that reduces contact, as evidenced by sea lice infections in migratory pink salmon [43]. Mechanisms that increase the force of infection during transience include: (g–f) movement through habitats with viable infective stages, which occurs with parasitic nematodes in migratory saiga [8] and dispersing pygmy blue tongue lizards [9]; (h) immunosuppression, such as the proliferation of latent bacterial infections in migratory redwing thrushes [44]; and (i) host aggregation, which occurs with avian influenza virus (AIV) infections during stopovers by migrating sandpipers [45]. (Online version in colour.)