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Figure 1 | Veterinary Research

Figure 1

From: Bridge hosts, a missing link for disease ecology in multi-host systems

Figure 1

Definition of different target-bridge-maintenance systems (adapted from Haydon et al. [ 10 ]). A represents the simplest maintenance-bridge-target system. In A’, the maintenance and target populations are less connected (frequency/intensity of infectious contacts) than between the maintenance-bridge-target populations. In B, mitigation strategies aimed at one bridge host cannot fully control pathogen transmission to the target host because of the alternative bridge host’s pathway. If both maintenance populations were in contact with both bridge hosts (i.e. if dashed arrows exist), controlling contacts between the target population and bridge hosts should be simpler than other control options. In B’, according to our definition, Z is not considered as a bridge population as it belongs to the maintenance community. In C, stopping contacts between the maintenance population and the target population by acting on one of the two bridge hosts would not be enough to stop transmission, which can still occur through the second bridge host. D is a special case of B, understanding the complexity of the maintenance community is not necessary to control the pathogen transmission risk to the target population, which can be achieved through the control of arrows connecting the bridge host. In E, none of the host populations can sustain the infection by itself and according to our definition, u is not considered as a bridge population as it belongs to the maintenance community. In F, the bridge host connects the target population with another maintenance host creating a system with a maintenance meta-population, which could change the epidemiological dynamics of the system and the probability of success of intervention strategies (e.g. vaccination coverage to achieve control of the infection in the target population). G is a special case where two bridge hosts are necessary to achieve the transmission function. Good knowledge of the ecological interactions in the ecosystem will be necessary to identify such complex interactions between bridge hosts.

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