title: Structural and Practical Identifiability Issues of Immuno-Epidemiological Vector-Host Models with Application to Rift Valley Fever.
abstract: In this article, we discuss the structural and practical identifiability of a nested immuno-epidemiological model of arbovirus diseases, where host-vector transmission rate, host recovery, and disease-induced death rates are governed by the within-host immune system. We incorporate the newest ideas and the most up-to-date features of numerical methods to fit multi-scale models to multi-scale data. For an immunological model, we use Rift Valley Fever Virus (RVFV) time-series data obtained from livestock under laboratory experiments, and for an epidemiological model we incorporate a human compartment to the nested model and use the number of human RVFV cases reported by the CDC during the 2006-2007 Kenya outbreak. We show that the immunological model is not structurally identifiable for the measurements of time-series viremia concentrations in the host. Thus, we study the non-dimensionalized and scaled versions of the immunological model and prove that both are structurally globally identifiable. After fixing estimated parameter values for the immunological model derived from the scaled model, we develop a numerical method to fit observable RVFV epidemiological data to the nested model for the remaining parameter values of the multi-scale system. For the given (CDC) data set, Monte Carlo simulations indicate that only three parameters of the epidemiological model are practically identifiable when the immune model parameters are fixed. Alternatively, we fit the multi-scale data to the multi-scale model simultaneously. Monte Carlo simulations for the simultaneous fitting suggest that the parameters of the immunological model and the parameters of the immuno-epidemiological model are practically identifiable. We suggest that analytic approaches for studying the structural identifiability of nested models are a necessity, so that identifiable parameter combinations can be derived to reparameterize the nested model to obtain an identifiable one. This is a crucial step in developing multi-scale models which explain multi-scale data.
authors.affiliation: Department of Mathematical Sciences, Florida Atlantic University, Science Building, Room 234, 777 Glades Road, Boca Raton, FL, 33431, USA. ntuncer@fau.edu.
authors.forename: Necibe
authors.initials: N
authors.lastname: Tuncer
authors.affiliation: School of Biology and School of Mathematics, Georgia Institute of Technology, 310 Ferst Dr., Atlanta, GA, 30332, USA.
authors.forename: Hayriye
authors.initials: H
authors.lastname: Gulbudak
authors.affiliation: Department of Biology, University of Florida, 220 Bartram Hall, PO Box 118525, Gainesville, FL, 32611-8525, USA.
authors.forename: Vincent L
authors.initials: VL
authors.lastname: Cannataro
authors.affiliation: Department of Mathematics, University of Florida, 358 Little Hall, PO Box 118105, Gainesville, FL, 32611-8105, USA.
authors.forename: Maia
authors.initials: M
authors.lastname: Martcheva
mesh_terms: D000818:Animals; D001179:Arthropod Vectors / Q000821:virology; D004196:Disease Outbreaks; D054884:Host-Pathogen Interactions / Q000276:immunology*; D006801:Humans; D058751:Livestock; D055641:Mathematical Concepts; D018448:Models, Immunological; D012295:Rift Valley Fever / Q000453:epidemiology* / Q000276:immunology* / Q000635:transmission; D012296:Rift Valley fever virus / Q000276:immunology / Q000472:pathogenicity
keywords: Arbovirus diseases; Immune dynamics; Immuno-epidemiological modeling; Parameter estimation; Rift Valley fever; Structural and practical identifiability analysis