Zoonotic Disease Transmission May Be Linked to Host Co-Occurrence Network Topology.

Most human pathogens are zoonotic, transmitted from vertebrate hosts to humans. However, it is still unclear how the topology of host co-occurrence networks may contribute to disease transmission. To address this uncertainty, we examined the host co-occurrence networks of 22 zoonotic pathogens from six continents (70 networks). First, we distinguished two major gradients of variability in host network topology-size (numbers of nodes and edges) and connectance/modularity. Larger networks with high connectance but low modularity have a greater potential for zoonotic disease transmission. These networks encompassed the hosts of 10 pathogens that cause emerging, re-emerging, and/or genetically diversifying diseases: St. Louis encephalitis virus, influenza A virus, West Nile virus, Toxoplasma gondii, Eastern equine encephalitis virus, Avian orthoavulavirus 1, Japanese encephalitis virus, Usutu virus, Sindbis virus, and Coxiella burnetii. Second, we identified the top 87 hosts with the most connections to other hosts across networks, for example, Columba livia (rock pigeon), Passer domesticus (house sparrow), Hirundo rustica (barn swallow), Sturnus vulgaris (European starling), Anas platyrhynchos (mallard), and Gallinula chloropus (common moorhen). These species were highly connected in 7-27 networks of 2-11 pathogens. Notably, 50 of the 87 hosts were migratory, urban, or semi-urban, highlighting the risk of zoonotic spread in developed areas.