Work needs to be organized from the outset in a manner that both recognizes and respects individual disciplinary approaches, but that also cuts across them in a truly interdisciplinary manner in order to deliver genuine integration, both between disciplines and across localities. Although frequently ignored in the natural sciences, we propose a clear interdisciplinary conceptual framework (as is more common in interdisciplinary social science work, such as development studies) to capture the integration across all scales that is required (). Our framework integrates dynamic interactions between bats, viruses, intermediate livestock hosts and people in a local system, influenced by wider environmental, social and politico-economic drivers. is inspired by a range of research fields, drawing together perspectives from medical and veterinary (virology, epidemiology, public health), environmental (ecology, biodiversity) and social (anthropology, politics, science–policy studies) sciences. Each key element of the framework comprises a potential research theme within which specific questions can be investigated; importantly, novel insights and policy impacts should be derived from their integration.
A conceptual framework for the study of wildlife derived zoonoses, focused on bat infections.
Thus, in , the central rectangle portrays the inter-linked spectrum of dynamics involved in zoonotic spillover and disease emergence: bat population dynamics, their effects on viral pathogen dynamics, the dynamics of human exposure [45
], including the involvement of domesticated species and the effects of the pathogens on human health and wellbeing.
The dynamics of individual spillover events are based around the concept of the pyramid (triangle here) of pathogen emergence first proposed by Antia [26
] and developed further by others, including Lloyd-Smith et al.
]. It is proposed that humans are constantly challenged by animal-derived pathogens (the so-called pathogen, or viral, ‘chatter’), but that only a small proportion manage to invade individual humans. Of those invading, most will be controlled by innate immunity and not replicate efficiently. Of those (proportionally) few that manage to replicate within the new host, most will not be able to transmit between individuals, or will do so only very poorly. As reviewed [27
], the major determinant of whether these replicating pathogens will then invade human populations is the rate at which they can transmit between humans.
Our framework also captures how intermediate hosts, such as livestock, can play key bridging roles in such spillover events. Bridging species have been particularly important for many of the most serious bat-derived human pathogens, including the horse for Hendra virus [12
], the pig for the initial emergence of Nipah virus [49
], non-human primates in the case of Ebola [50
] and the palm civet in the case of SARS-coronavirus [52
]. The disease impact on bridging species can have severe human wellbeing implications in its own right, as exemplified by the decimation of the pig industry in Malaysia as a consequence of Nipah virus emergence [53
Spillover dynamics are subject to a range of local influences and practices, both social and environmental, including environmental influences1
on viral pathogen dynamics, such as interactions with susceptible sympatric species. Land use, wildlife management and conservation practices
can shape bat ecology and populations. The interactions between bats and ecosystems are manifold; through seed dispersal and pollination, bat populations also influence ecological structure and functioning. Infection dynamics are shaped by (and can, in turn, feed back to shape) bat ecology
and related ecosystem processes; in turn, infection dynamics influence spillover dynamics. Human–bat interactions
, including livelihood and ritual practices, bring different people into contact with bats and potentially expose them to disease. The public perception of bats and bat diseases can trigger eradication efforts that may then increase spillover risks. Public health impacts and detection
, including disease surveillance and diagnostics for known pathogens (and capacity to detect previously unrecognized pathogens through newly evolving ‘pathogen discovery’ techniques [21
]) and health-seeking practices, shape whether human infections with bat-derived pathogens are recognized. Such local system dynamics are shaped by wider drivers
of change (environmental, social, political and economic), operating across different geographical scales. Importantly, our framework integrates a focus on political, cultural and policy framings
, examining how different people in communities and in national and international agencies understand and represent spillover dynamics, public health threats and influences, and how these framings shape policy responses. Finally, we attend to how local system dynamics are shaped by wider drivers of change—environmental, economic, demographic, social—operating across local, regional, national and global scales. Taken together, bats provide a model for these framework elements, which should provide the evidence required to inform a series of ‘one health’ interventions and policy impacts, and assist the building of new interdisciplinary capabilities for research, policy engagement and disease mitigation while also enabling the conservation of biodiversity.