Quantifying host species contributions to pathogen transmission in a multihost community: the case of chytrid fungus in amphibian communities

Lead Research Organisation: Zoological Soc London Inst of Zoology
Department Name: Institute of Zoology


Many pathogens of global health and conservation concern infect multiple host species. Ebola is a classic example, circulating naturally within a 'reservoir' host community, and with the potential to jump across to another host species with devastating effect. Clearly it is vital to understand how such pathogens are maintained in their host communities, and which species play a major role in spreading those pathogens. However, obtaining that understanding is notoriously hard. We have recently developed a mathematical approach to measure a host community's ability to maintain a pathogen, and identify 'key hosts' that drive pathogen spread. Importantly, unlike previous methods, this approach can be parameterised using relatively coarse-grained, easily-collected data (standard measures of host abundance and infection occurrence). We will provide the first rigorous test of this model, applying it to a natural 'multihost'-pathogen system of major conservation concern: chytrid fungus ('Bd') in amphibian communities. Bd is a major cause of amphibian declines worldwide, but we don't understand how it spreads through or is maintained by amphibian communities. We will apply our mathematical approach to historical and new data, and use it to identify those key hosts, and predict the effect of removing them. Crucially, we will then directly test those predictions by carrying out species removal experiments. Overall this will provide a rigorous test of our mathematical tool, show how host communities affect pathogen spread in general, and provide specific guidelines for the management of Bd in particular.

Planned Impact

Chytridiomycosis affects wildlife communities globally and has devastated amphibian communities on four continents. There are major efforts to prevent its spread and manage its impact, but in every case the focus is on single host species conservation. This is clearly inadequate, as in every system where conservation efforts are underway the single host exists within a host community where potential reservoir species have been identified. By developing the analytical tool that allows the identification of key reservoir species and predicts the impact of removal, we hope to shift efforts to conserve single species threatened by chytridiomycosis to efforts to manage amphibian communities so that they may coexist with infection. Many relevant amphibian communities are found in structured habitats where management strategies that our method would recommend are possible. For example, across Europe and in North America threatened host populations are predominantly within high elevation communities where breeding habitat is spatially segregated and reproduction is broadly temporally predictable for component species. The fact that our study site is the index site where the first case of Bd was recorded in Europe - and where it is still continuing to circulate - is an example of this and makes our study particularly relevant, and important, for those working on the management of this disease. This group of stakeholders is not restricted to academics: field management of amphibian communities falls under the remit of government agencies, park managers, private landowners and NGOs committed to wildlife conservation. As well, current efforts to conserve amphibians threatened by chytridiomycosis overwhelmingly include a captive assurance component, where species threatened with extinction due to Bd are kept and bred in captivity until such time the threat has been mitigated. Because of limited infrastructure to support these efforts, amphibians are housed in mixed species facilities, where despite the best efforts at maintaining biosecurity, outbreaks of disease do occur. Our analytical approach can be applied to these settings, and can be used to guide how the various stakeholder facilities share responsibilities for captive assurance and structure their collections to minimize the possibility of outbreaks.
More broadly, our work will also be highly relevant to policy makers and those involved in the practical management of multihost diseases in general. Given that most emerging diseases involve multiple host species, it is clearly vital to understand the processes by which diseases circulate within and impact upon natural host communities. The majority of infectious diseases that are affecting livestock, crops and humans spill over from wildlife hosts and are maintained in wildlife communities. Host species responsible for spill over events are frequently identified but unlikely to be eliminated from contacts with susceptible spill over hosts (eg camels and MERS). What is instead needed is a toolkit that allows the identification of host community structures that pose the greatest risk for propagating spill over events. By using our system to develop and validate our generalised theoretical framework, this study has the potential to produce an invaluable tool for quantifying host contributions to transmission that can easily be applied by managers to other contexts and communities. As such, our study should influence the efforts of those who work to mitigate a wide range of multi-host diseases, by providing a validated framework with which to quantify the processes that underpin pathogen circulation and impact within natural communities.


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Description Our key finding is that amphibian communities we focused on are actual subject to the impacts of multiple pathogens, typically in sequence. in response, we have redirected some of our efforts into examining how multiple pathogens (chytrid fungi and ranaviruses) circulate in amphibian host communities and have developed experimental system to investigate this. We have expanded this programme to integrate the findings of two other NERC-funded projects, where we determined amphibian skin microbiomes are interacting with each of these pathogen types.
Exploitation Route To soon to say
Sectors Environment

Description ACCE NERC DTP
Amount £90,000 (GBP)
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 09/2017 
End 10/2021
Description Departmental lecture at North West University, RSA 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact Lecture to the post-graduate students and conservation course on assessing local, regional and global risk of chytridiomycosis in amphibian communities. The audience included students on the conservation course, attendees of a workshop on ethics and welfare, post-graduate students and some faculty. Delivery of lecture is part of my responsibilities as an extraordinary professor at the university, a post I was awarded largely due to my long-standing and NERC-funded research programme on chytridiomycosis
Year(s) Of Engagement Activity 2018
Description Mitigating single pathogen and co-infections that threaten amphibian biodiversity 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact First major scientific event examining how to mitigate single and multiple pathogens in amphibian populations threatened by infectious diseases. Conveners include PIs from 3 NERC standard grants. 2 day symposium involving researchers from across Europe, the Americas and Australasia, and 2 single day workshops, 1 on microbiomes and 1 doing a mock disease intervention. One publication from 2nd workshop. Attendees report overwhelmingly as to quality and reach of event, new collaborations formed and suggestion this become a once every few years event.
Year(s) Of Engagement Activity 2019
Description Training on IoZ contribution to training on the London DTP and the Oxford DTP 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Postgraduate students
Results and Impact I contributed to our annual event hosting PhD candidates on two NERC-funded DTPs. The core content of my presentation was constructed around current research on my NERC-funded projects, and providing PhD candidates the opportunity to become aware of the opportunities and support that could be provided to them through existing NERC projects. Some of the participants contacted me for further information about methods, contacts and the possibility of involvement in the research programmes
Year(s) Of Engagement Activity 2017