Critical Review on the Public Health Impact of Norovirus Contamination in Shellfish and the Environment: A UK Perspective

Abstract

We review the risk of norovirus (NoV) infection to the human population from consumption of contaminated shellfish. From a UK perspective, risk is apportioned for different vectors of NoV infection within the population. NoV spreads mainly by person-to-person contact or via unsanitary food handling. NoV also enters the coastal zone via wastewater discharges resulting in contamination of shellfish waters. Typically, NoV persists in the marine environment for several days, with its presence strongly linked to human population density, wastewater discharge rate, and efficacy of wastewater treatment. Shellfish bioaccumulate NoV and current post-harvest depuration is inefficient in its removal. While NoV can be inactivated by cooking (e.g. mussels), consumption of contaminated raw shellfish (e.g. oysters) represents a risk to human health. Consumption of contaminated food accounts for 3–11% of NoV cases in the UK (~74,000 cases/year), of which 16% are attributable to oyster consumption (11,800 cases/year). However, environmental and human factors influencing NoV infectivity remain poorly understood. Lack of standard methods for accurate quantification of infective and non-infective (damaged) NoV particles represent a major barrier, hampering identification of an appropriate lower NoV contamination limit for shellfish. Future management strategies may include shellfish quality assessment (at point of harvest or at point of supply) or harvesting controls. However, poor understanding of NoV inactivation in shellfish and the environment currently limits accurate apportionment and risk assessment for NoV and hence the identification of appropriate shellfish or environmental quality standards.

F-Specific RNA Bacteriophages, Especially Members of Subgroup II, Should Be Reconsidered as Good Indicators of Viral Pollution of Oysters

“…Hence, the first phase could be associated with the elimination of viral particles, while the second phase could just be the result of the degradation of residual genomes present in shellfish, leading to concentrations close to the LOD, as determined using the ISO 15216-1 standard (18) (i.e., 40 gc/g of HP in the best case), and, thus, amounts hardly quantifiable in such samples. Taking into account the striking persistence of genomes compared to that of viral particles, the 28-day minimum closure period for shellfish production areas, established following a significant pollution incident or a known NoV outbreak, may need to be discussed (30,65).…”

“…It can be 10 to 100 times higher because of the small volume analyzed by reverse transcription (RT)-PCR, the low recovery rate during genome extraction, and the presence of (RT-)PCR inhibitors. Thus, except in some specific cases (i.e., in cases with very high levels of pollution or artificial contamination) (26,27), the number of genome copies of NoV in oysters is usually close to the limit of detection (16,(28)(29)(30)(31), and all these considerations highlight the difficulties in interpreting a positive or a negative result when using such an approach.…”

Detection of Infectious Noroviruses from Wastewater and Seawater Using PEMAXTM Treatment Combined with RT-qPCR

“…Irrespective of wastewater treatment type, enteric viruses including noroviruses are likely to be present at concentrations up to 5 log 10 genome copies in non-disinfected wastewater effluents. When virus-contaminated effluent is released into receiving environmental waters there are associated human health risks through environmental transmission [19,24]. Demonstration of virus infectivity in these waters is required to assess risk.…”

A global review of the ecosystem services provided by bivalve aquaculture

“…Bivalves are filter feeders, and in areas of lower water quality can bioaccumulate bacteria, protozoa and viruses that are harmful to human health (Roslev et al 2009;Clements et al 2013). Oysters, mussels, clams and cockles are able to concentrate environmental elements and sewage related microbes within their tissues, (Alexander 1976;Daskin et al 2008;Fukumori et al 2008;Kovacs et al 2010;Hassard et al 2017). This causes potential trade-offs with human consumption.…”