title: Serological investigations of emerging viral zoonoses: Crimean-Congo haemorrhagic fever virus in Tanzania and severe acute respiratory syndrome coronavirus 2 in Scotland
Creators: name: Hughes, Ellen Clare
Publisher: name: University of Glasgow
Year: 2022

description: Emerging viral zoonoses are a significant global health concern, brought into sharp focus in recent times by the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the subsequent global pandemic. Other emerging and re-emerging zoonotic viruses also continue to present significant threats to public health, including Crimean-Congo haemorrhagic fever virus (CCHFV), a tick-borne virus that can cause severe disease and high case fatality rates in people, but with a complex ecology that remains poorly understood in many areas of the world, particularly in Africa. Serological tools are vital for understanding emerging zoonotic viruses both at a population- and individual-level. Population-level surveillance of animal and human populations can shed light on patterns of viral circulation and aid in identification of risk factors associated with infection, while individual-level serological investigations help to characterise the immune response to infection, providing insights into the nature of protective immunity, possible vaccine targets and improving methods of disease detection. The initial focus of this thesis was the development of a diagnostic enzyme-linked immunosorbent assay (ELISA) for detection of CCHFV, and its subsequent use to explore the epidemiology of the virus in livestock and people in northern Tanzania. However, the start of the coronavirus disease 19 (COVID-19) pandemic part way through this research resulted in an additional set of research questions relating to SARS-CoV-2 diagnostic assay performance and epidemiology during the first wave of the pandemic in Glasgow, UK. This thesis therefore explores diagnostics assay development and epidemiology of CCHFV and SARS-CoV-2. Firstly, an indirect ELISA for detection of anti-CCHFV antibodies in livestock was developed and optimised. It showed good potential for use as an in-house assay for detection of CCHFV exposure in animals. Secondly, the performance of two indirect ELISA assays against the S1 subunit of the SARS-CoV-2 spike protein (S1) and the receptor binding domain (RBD) was investigated, establishing a cut-off value for interpretation of these assays, determining sensitivity and specificity, and exploring measures of assay precision. Both assays showed good ability to distinguish between positive or negative serum samples for anti-SARS-CoV-2 IgG antibodies. These ELISAs were then used to investigate levels of SARS-CoV-2 exposure in a patient population in Glasgow during the first wave of the COVID-19 pandemic, demonstrating that overall seroprevalence remained low throughout this period. Additionally, ELISA responses were compared against levels of neutralising antibodies (NAbs), measured using HIV(SARS-CoV-2) pseudotype virus neutralisation assays (PVNAs), demonstrating heterogeneity in IgG and NAb responses, and highlighting an association between disease severity and higher levels of IgG and neutralising antibodies. The epidemiology of CCHFV in northern Tanzania was explored through analysis of a large cross-sectional study of livestock and people in linked households, using a commercially produced species-independent ELISA. This study demonstrated for the first time that CCHFV is circulating in northern Tanzania. High levels of exposure were found in cattle (n = 1530/3098, 49.4%), goats (n = 823/2475, 33.3%), and sheep (n = 582/2124, 27.4%) across the region, and an overall seroprevalence of 15.1% (n = 53/351) was observed in people, despite an absence of confirmed clinical disease in the country (Temur et al., 2021). Substantial heterogeneities were observed in levels of exposure between study sites for both livestock and people, indicating that local context is important for determining exposure to CCHFV. However, patterns of village-level exposure varied between people and livestock, possibly suggesting different drivers of exposure. Risk factors associated with CCHFV seropositivity were also investigated in livestock, and demonstrated that increasing age, and extensive, pastoral agro-ecological settings were associated with higher levels of exposure. Additionally, a novel association was identified between pig keeping and higher exposure in cattle. The work presented in this thesis demonstrates the application of serological methods for investigation of two important emerging and re-emerging zoonotic viruses, SARS-CoV-2 and CCHFV. This research adds substantially to our knowledge of CCHFV epidemiology in northern Tanzania, demonstrating high levels of exposure to the virus in livestock populations and highlighting its potential as a public health concern in the country, while the work on SARS-CoV-2 provided important information on population-level immunity and the nature of the immune response during the early phases of the global pandemic.