The Transmission of Enteric Viruses through the Aquatic Environment in the UK

Abstract

Hepatitis E virus (HEV) and norovirus are known enteric pathogens which can cause a wide range of symptoms. Norovirus is estimated to cause 3 million cases in the UK annually, and whilst HEV cases are reported at much lower levels, it is considered to be an emerging pathogen within more economically developed countries and may be an underestimated health risk. However, the routes of transmission for HEV have not yet been fully elucidated. This PhD endeavours to identify whether the aquatic environment plays a significant role in the transmission of HEV, using norovirus for comparison of prevalence and risk. The studies within this PhD identified HEV and norovirus within sewage and shellfish samples and identified HEV within cetacean liver samples. Sequencing of these samples confirmed norovirus presence within sewage and confirmed HEV presence in sewage and shellfish samples. Additionally, a HEV sequence within a shellfish sample may be classified as a new subtype of genotype 3 and the norovirus genotypes identified within sewage suggest that wastewater monitoring of norovirus may be beneficial for identifying circulating norovirus genotypes. A risk assessment of norovirus and HEV presence in sewage and shellfish samples showed that the risk of norovirus illness from recreational water activities and shellfish consumption may be high, but that risk of HEV illness was very low in comparison. Overall, HEV is present within the aquatic environment in the UK, however the prevalence and levels of HEV in sewage and shellfish suggest that its presence provides little risk to public health. On the other hand, contamination of norovirus within the aquatic environment is a systemic problem in the UK, which is not without public health risk, and must be addressed through limiting release of raw sewage into the environment, standardisation of wastewater treatment practices to make them more effective for removal of viruses.