Waterborne, abiotic and other indirectly transmitted (W.A.I.T.) infections are defined by the dynamics of free-living pathogens and environmental reservoirs

Miles D. Miller-Dickson; Victor A. Meszaros; Francis Baffour-Awuah; Salvador Almagro-Moreno; C. Brandon Ogbunugafor

In this study, we develop the "waterborne, abiotic and other indirectly transmitted" (W.A.I.T. or WAIT) paradigm, a generalized framework for understanding "sit and wait" pathogens that are indirectly transmitted through an environmental reservoir intermediate. As the WAIT perspective specifically focuses on the peculiar dynamics of environmental compartments, we argue that it is imbued with more features and applies to a broader set of examples than prior treatments. To demonstrate its novelty and range of application, we fully examine its common relevance to two otherwise disparate modern diseases: cholera and hepatitis C virus. The study proceeds in stages: (1) we first introduce a purely theoretical iteration of WAIT using a standard epidemiological model, explaining how to conceptualize an infection in terms of the WAIT framework, and deriving the reproductive number (R 0 ) using analytical methods. (2) We apply the WAIT perspective to a waterborne disease that has been the object of several modeling exercises: the transmission of Vibrio cholerae in a densely populated setting with limited access to clean drinking water. (3) We then apply the WAIT perspective to a completely different, less-explored disease case: an HCV epidemic among injection drug users (IDU) in a modern urban setting. These constitute different epidemics in terms of pathogen type (Vibrio cholerae is a Gram-negative bacterium, HCV a single-stranded RNA virus) and setting. Nonetheless, we conceptualize and model each epidemic scenario, highlighting mathematical features that are unique to the WAIT framework. We discuss how this lens provides new perspective on cholera outbreaks and especially the modern HCV epidemic.