title: Breaking beta: deconstructing the parasite transmission function.
abstract: Transmission is a fundamental step in the life cycle of every parasite but it is also one of the most challenging processes to model and quantify. In most host-parasite models, the transmission process is encapsulated by a single parameterβMany different biological processes and interactions, acting on both hosts and infectious organisms, are subsumed in this single term. There are, however, at least two undesirable consequences of this high level of abstraction. First, nonlinearities and heterogeneities that can be critical to the dynamic behaviour of infections are poorly represented; second, estimating the transmission coefficientβfrom field data is often very difficult. In this paper, we present a conceptual model, which breaks the transmission process into its component parts. This deconstruction enables us to identify circumstances that generate nonlinearities in transmission, with potential implications for emergent transmission behaviour at individual and population scales. Such behaviour cannot be explained by the traditional linear transmission frameworks. The deconstruction also provides a clearer link to the empirical estimation of key components of transmission and enables the construction of flexible models that produce a unified understanding of the spread of both micro- and macro-parasite infectious disease agents.This article is part of the themed issue 'Opening the black box: re-examining the ecology and evolution of parasite transmission'.
authors.affiliation: Environmental Futures Research Institute, Griffith University, Nathan 4111, Queensland, Australia h.mccallum@griffith.edu.au.
authors.forename: Hamish
authors.initials: H
authors.lastname: McCallum
authors.affiliation: Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK.
authors.forename: Andy
authors.initials: A
authors.lastname: Fenton
authors.affiliation: Center for Infectious Disease Dynamics, Penn State University, University Park, PA 16802, USA.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Hudson
authors.affiliation: School of Natural Sciences, University of Stirling, Stirling FK9 4LA, UK.
authors.forename: Brian
authors.initials: B
authors.lastname: Lee
authors.affiliation: Institute of Integrative Biology, University of Liverpool, Liverpool L69 7ZB, UK.
authors.forename: Beth
authors.initials: B
authors.lastname: Levick
authors.affiliation: School of Natural Sciences, University of Stirling, Stirling FK9 4LA, UK.
authors.forename: Rachel
authors.initials: R
authors.lastname: Norman
authors.affiliation: School of Biosciences, Cardiff University, Museum Avenue, Cardiff CF10 3AX, UK.|Department of Biodiversity and Molecular Ecology, Research and Innovation Centre, Fondazione Edmund Mach, Via E. Mach 1, 38010 S. Michele all'Adige, Trentino, Italy.
authors.forename: Sarah E
authors.identifier: http://orcid.org/0000-0002-7457-2699
authors.initials: SE
authors.lastname: Perkins
authors.affiliation: School of Biological Sciences, University of Bristol, Tyndall Avenue, Bristol BS8 1TQ, UK.
authors.forename: Mark
authors.identifier: http://orcid.org/0000-0002-4857-1238
authors.initials: M
authors.lastname: Viney
authors.affiliation: Vector-borne Viral Diseases Programme, The Pirbright Institute, Ash Road, Pirbright, Woking GU24 0NF, UK.
authors.forename: Anthony J
authors.identifier: http://orcid.org/0000-0002-2000-2914
authors.initials: AJ
authors.lastname: Wilson
authors.affiliation: School of Biosciences, Cardiff University, Museum Avenue, Cardiff CF10 3AX, UK LelloJ@cardiff.ac.uk.|Department of Biodiversity and Molecular Ecology, Research and Innovation Centre, Fondazione Edmund Mach, Via E. Mach 1, 38010 S. Michele all'Adige, Trentino, Italy.
authors.forename: Joanne
authors.identifier: http://orcid.org/0000-0002-2640-1027
authors.initials: J
authors.lastname: Lello
mesh_terms: D000820:Animal Diseases / Q000635:transmission*; D000818:Animals; D006790:Host-Parasite Interactions; D008962:Models, Theoretical; D010271:Parasites / Q000502:physiology*; D011157:Population Dynamics
keywords: heterogeneity; infection; infectious disease; modelling; nonlinearities; transmission function