Hepatitis C virus modelled as an indirectly transmitted infection highlights the centrality of injection drug equipment in disease dynamics

Abstract

<jats:p>The hepatitis C virus (HCV) epidemic often occurs through the persistence of injection drug use. Mathematical models have been useful in understanding various aspects of the HCV epidemic, and especially, the importance of new treatment measures. Until now, however, few models have attempted to understand HCV in terms of an interaction between the various actors in an HCV outbreak—hosts, viruses and the needle injection equipment. In this study, we apply perspectives from the ecology of infectious diseases to model the transmission of HCV among a population of injection drug users. The products of our model suggest that modelling HCV as an indirectly transmitted infection—where the injection equipment serves as an environmental reservoir for infection—facilitates a more nuanced understanding of disease dynamics, by animating the underappreciated actors and interactions that frame disease. This lens may allow us to understand how certain public health interventions (e.g. needle exchange programmes) influence HCV epidemics. Lastly, we argue that this model is of particular importance in the light of the modern opioid epidemic, which has already been associated with outbreaks of viral diseases.</jats:p>

The Epidemiological Signature of Pathogen Populations That Vary in the Relationship between Free-Living Parasite Survival and Virulence

“…The model is implemented via a set of ordinary differential equations, defined by Equations (1)–(6). It implements viral free-living survival via the “Waterborne Abiotic or other Indirect Transmission (WAIT)” modelling framework, coupling individuals and the pathogen within the environment [ 23 , 24 ].…”

Variation in microparasite free-living survival and indirect transmission can modulate the intensity of emerging outbreaks

“…This model is derived from a previously developed framework called “WAIT”—which stands for Waterborne, Abiotic, and other Indirectly Transmitted —that incorporates an environmental reservoir where a pathogen remains in the environment and “waits” for hosts to interact with it 11 , 12 . The supplementary information contains a much more rigorous discussion of the modeling details.…”

“…This is useful in the case of emerging diseases, where it may be challenging to fully resolve all of the features of an epidemic, including the influence of different routes of transmission on key features of an epidemic. That is, even though there is a large general literature on environmental transmission (or "fomite" transmission) [1][2][3][4][5][6][7][8][9][10][11][12][13] , relatively few studies have explored how particular aspects of indirect or environmental transmission can influence disease dynamics. Lack of clarity regarding how variation in environmental transmission (e.g.…”

The epidemiological signature of pathogen populations that vary in the relationship between free-living survival and virulence

“…The model is implemented via a set of ordinary differential equations, defined by Equations 1.1 -1.6. It implements viral free-living survival via the "Waterborne Abiotic or other Indirect Transmission (WAIT)" modelling framework, coupling individuals and the pathogen within the environment [27,28].…”