Virus transfer at the skin-liquid interface and its associated risks

Infectious diseases are a leading cause of death across the world. One of the primary causes of infectious diseases are viruses. Since liquids are highly important in the transmission of viruses, the aims of this work are to i) quantify the transfer of viruses at the interface between liquids and people, ii) understand the factors influencing this transfer, and iii) illustrate some of the risks associated with people's interaction with contaminated liquids. After a brief introduction, Chapter 2 introduces a method to quantify virus transfer at the skin-liquid interface and presents the results of a series of human subject studies performed using two non-enveloped (MS2 and Qβ) and one enveloped bacteriophage (Ί6) as pathogenic virus surrogates. Findings from these studies include models of liquid-to-skin and skin-to-liquid transfer. Briefly, the number of viruses transferred from liquid-to-skin per surface area is describable by a single model based on 1) the concentration of virus in the liquid, and 2) the film thickness of the liquid remaining on the skin. This model accounts for the viruses adsorbed on the skin and the viruses in the liquid retained on the skin. Factors such as contact time and liquid conditions (pH and ionic strength) had no influence on virus transfer. In Chapter 3, bacteriophage MS2 was used to test different skin surrogates by comparing virus transfer rates in a volunteer trial to those obtained using human cadaver skin and synthetic skin. MS2 transfer to volunteer skin was similar to cadaver skin but significantly different than to synthetic skin. Having found an appropriate skin surrogate, the transfer of two enteric pathogenic viruses (adenovirus and coxsackievirus) from liquid to cadaver skin was quantified and compared with the transfer of one bacteriophage (MS2). The amount of MS2 adsorbed on the skin was five times higher than adenovirus and four times higher than coxsackievirus. Therefore, quantification of pathogenic virus retention on the skin would thus be overestimated using MS2 adsorption data. Results obtained in Chapter 2 and 3 revealed the importance of the volume of liquid retained on the skin on the number of viruses transferred from liquid-to-skin. Therefore Chapter 4 describes the results of a series of human subject studies performed to quantify the volume of liquid retained on the skin after different activities. In these studies, factors such as the activity performed and the age category of the volunteers influenced the volume of liquid retained on the skin. Finally, Chapter 5 presents overall conclusions from the work, along with examples on the use of the data in risk assessments. Overall, the presented work offers estimates for the transfer of viruses at the interface between liquids and people, a methodology to obtain those estimates for other pathogens of human health concern, and examples on how the estimates have been applied in the past and how they can be applied in the future. Findings from this thesis are a small contribution to the microbial risk assessment field, which may aid in designing cost-effective interventions to control the spread of infectious diseases.