Modelling the spread of Sphaerothecum destruens, a generalist fungal pathogen.

Humans have altered the global landscape with agriculture, urban development and international trade, and the incidence of emerging infectious diseases (EIDs) has increased as a result. Pathogens can emerge in new areas as a direct result of global transport trade or indirectly due to climate–mediated shifts in parasite geographic range. These pathogens can cause considerable ecological and economic damage, as they accelerate biodiversity loss and threaten global food security. Furthermore, the inherent characteristics of pathogens allow their rapid evolution, intensifying their potential threat. Fungi and fungal-like pathogens are an increasing component of EIDs with highly opportunistic features. One group of these pathogens on the animal-fungal boundary is the Mesomycetozoea, a group which has raised ecological concerns for a range of susceptible host species including birds, amphibians and mammals. To be able to mitigate the impacts of these pathogens effectively, their dynamics and drivers must be better understood. Using the only Mesomycetozoea fungal species that has been cultured to date, the generalist pathogen Sphaerothecum destruens, empirical data on infectivity and pathogen life cycle were used in several epidemiological models to explore how a fungal-like generalist is transmitted within different host communities. First, a single host system was created using the available empirical data. This demonstrated that multiple saturation functions were needed to parameterise the model accurately, and identified incubation and recovery rates as drivers of epidemics. The parameter values obtained from the single-host models enabled the characterisation of mathematical relationships between different parameters, a task which can be difficult in epidemiology. Following this, a multi-host model was used to examine pathogen establishment in different communities. The roles of community structure and composition were explored, including the influence of competitive interactions between host species. Host density, proximity between communities, the competitive interactions between species, and the persistence of free-living pathogen propagules were identified as important factors in disease emergence and community survival. Environmental transmission was a key pathway for pathogen establishment. Finally, the evolution of S. destruens’ virulence was explored in different conditions and for various transmission strategies. Direct contact and environmental uptake rates were key determinants of pathogen evolutionary stable strategy. Host eradication and selective restocking were evaluated as disease management techniques, examining the advantages and possible repercussions of each approach in light of the pathogen’s ecological and evolutionary dynamics. Mathematical models have been crucial in expanding ecological and epidemiological knowledge in other pathogens, allowing the exploration of diverse conditions and hypotheses about disease dynamics. The reliability of the results and their applicability were greatly enhanced by the inclusion of empirical data, giving this research substantial advantage in the robustness of model outputs. This work provided new insights on how fungal and fungal-like pathogens are transmitted and the risks of establishment in different populations, and can be applied to similar emerging pathogens, especially those that are fungi and fungal-like.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

Bournemouth University

Year dc:date.issued

2016

Author dc:creator

• Al-Shorbaji, Farah N.

Language dc:language

en