Abstract
Hepatitis E virus (HEV) is a leading cause of acute hepatitis globally. Previously believed tobe a disease restricted to developing nations, HEV is in fact distributed globally and is responsible for both sporadic and large-scale outbreaks of viral hepatitis. In the United Kingdom, a steady increase in the number of cases of non-travel related hepatitis E virus (HEV) infection has been observed in recent years. In Scotland there has been a substantial increase in the number of laboratory reports of non-travel associated HEV infections (http://www.hps.scot.nhs.uk/ewr/article.aspx). Despite the increase in the number of cases of autochthonous hepatitis E infection in Scotland, there is a distinct lack of information regarding transmission routes. Foodborne transmission of HEV is a major route of infection in Europe with contaminated food products such as leafy green vegetables, sausages and soft fruits being potential sources of transmission. Consumption of shellfish has also been identified as a possible risk factor of foodborne transmission of HEV to humans. To date, no studies in Scotland (or the United Kingdom) have been undertaken to assess the presence of HEV in commercially harvested blue mussels and Pacific oysters at point of sale in retailers. The main focus of the research project was to determine whether HEV was present in Scottish bivalve molluscs that were available at point of sale. The study also aimed to identify a reliable and effective method for the isolation and extraction of HEV from shellfish tissues. Despite the wide range of methods that are available for HEV extraction and RNA purification from animals, food and environmental samples, no methods have been standardized or validated. Moreover, it is difficult to make direct comparisons between studies because of the use of various extraction and detection methods that have been used across different studies. The methods evaluated as part of this study included a proteinase K digestion method set out in the technical specification ISO/TS 15216-1, and a cetyltrimethyl ammonium bromide based mollusc-specific total RNA extraction kit. Although these have not been validated for HEV, it was demonstrated that both methods resulted in successful detection of HEVin mussels and oysters. Neither method (the ISO/TS15216-1 method or the commercial mollusc-specific extraction kit) was demonstrably superior for HEV isolation and extraction from mussels; both methods were comparable in terms of the HEV detection rates obtained. Overall, 3.3% of mussels processed by proteinase K digestion and 2.7% of mussels processed individually using the mollusc-specific kit tested positive for HEV RNA by nested RT-PCR whilst 10.3% of oyster RNA extracted by various methods tested positive for HEV RNA. One of the most significant findings to emerge from this study was that phylogenetic analysis of the HEV sequences isolated from commercial shellfish showed that all sequences belonged to genotype 3 HEV. This thesis documents for the first time, the presence of genotype 3 hepatitis E virus in commercially sold shellfish in Scotland.These findings may encourage further research that will help to address the gaps in the knowledge with respect to environmental contamination and foodborne transmission of HEV in Scotland and the rest of the United Kingdom. Hopefully the findings reported in this study will lead to larger studies exploring the extrinsic contamination of food by HEV, the risks posed by infected food handlers in the food supply chain and the effects of various cooking methods on HEV infectivity. These are areas of research that urgently need to be addressed.
| Date of Award | 2018 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Linda Scobie (Supervisor) & John Craft (Supervisor) |