Stability of human enteric viruses in seawater samples from mollusc depuration tanks coupled with ultraviolet irradiation

Role of Filter-Feeding Bivalves in the Bioaccumulation and Transmission of White Spot Syndrome Virus (WSSV) in Shrimp Aquaculture Systems

White spot syndrome virus (WSSV) poses a major risk to shrimp aquaculture, and filter-feeding bivalves on shrimp farms may contribute to its persistence and transmission. This study investigated the bioaccumulation and vector potential of WSSV in Pacific oysters (Crassostrea gigas), blue mussels (Mytilus edulis), and manila clams (Venerupis philippinarum) cohabiting with WSSV-infected shrimp. Sixty individuals of each species (average shell lengths: 11.87 cm, 6.97 cm, and 5.7 cm, respectively) cohabitated with WSSV-infected shrimp (Penaeus vannamei, average body weight: 16.4 g) for 48 h. In the experiments, bivalves accumulated WSSV particles in both the gill and digestive gland tissues, with the digestive glands exhibiting higher viral load (average viral load, 3.91 × 104 copies/mg), showing that the viral concentrations in bivalve tissues are directly influenced by seawater WSSV concentrations, reaching levels sufficient to induce infection and 100% mortality in healthy shrimp using tissue homogenates. After a 168 h release period in clean water, the WSSV levels in bivalve tissues decreased below the detection thresholds, indicating reduced transmission risk. These results highlight the role of bivalves as temporary reservoirs of WSSV in aquaculture settings, with the transmission risk dependent on the viral concentration and retention period. Our findings suggest that the management of bivalve exposure in WSSV-endemic environments could improve the biosecurity of shrimp farms.

Virus contamination and infectivity in beach environment: Focus on sand and stranded material

To assess the exposure of beachgoers to viruses, a study on seawater, sand, and beach-stranded material was carried out, searching for human viruses, fecal indicator organisms, and total fungi. Moreover, for the first time, the genome persistence and infectivity of two model viruses was studied in laboratory-spiked sand and seawater samples during a one-week experiment. Viral genome was detected in 13.6 % of the environmental samples, but it was not infectious (Human Adenovirus - HAdV, and enterovirus). Norovirus and SARS-CoV-2 were not detected. The most contaminated samples were from sand and close to riverine discharges. In lab-scale experiments, the infectivity of HAdV5 decreased by ~1.5-Log₁₀ in a week, the one of Human Coronavirus-229E disappeared in <3 h in sand. The genome of both viruses persisted throughout the experiment. Our results confirm viral contamination of the beach and suggest HAdV as an index pathogen for beach monitoring and quantitative risk assessment.

Viral uptake and stability in Crassostrea gigas oysters during depuration, storage and steaming

More stable than bacteria in environmental samples, enteric viruses are generally related to outbreaks of gastroenteritis caused by the consumption of contaminated oysters. This study evaluated: i) the dynamic processes of enteric viral models bioaccumulation by Crassostrea gigas oysters artificially contaminated; ii) the stability of these viruses in oysters in controlled temperature conditions and iii) the effect of UV light in inactivating these viruses in depurated oysters. Plaque assay (PA) was used to assess the infectivity of both viral models. Cell culture coupled with RT-qPCR (ICC-RT-qPCR) was used to measure infectious adenovirus type 2 (HAdV-2) genomes and qPCR to measure genome copies of murine norovirus (MNV-1). The virus uptake through bioaccumulation behave differently: HAdV-2 reached its peak of uptake faster than MNV-1. Both viruses showed high stability in oysters when maintained under 4 °C, but were completely inactivated in steamed oysters. The HAdV-2 was completely inactivated after 12 h of depuration with UV light and after 24 h without UV light. After 72 h of depuration, MNV-1 was still detected in both tanks, probably due to the stronger interaction of this virus with the oyster's tissues. This study demonstrated the importance of a secure depuration time in ensuring a clean and safe product, and that the steaming process is the safest way to prepare oysters for consumption.

Weekly Variation of Rotavirus A Concentrations in Sewage and Oysters in Japan, 2014-2016

Concentrations of rotavirus A, in sewage and oysters collected weekly from September 2014 to April 2016 in Japan, were investigated using RT-qPCR; results showed up to 6.5 log₁₀ copies/mL and 4.3 log₁₀ copies/g of digestive tissue (DT) in sewage and oysters, respectively. No correlation was found between rotavirus concentration in sewage and oysters and cases of rotavirus-associated gastroenteritis.

Decay of sewage-associated bacterial communities in fresh and marine environmental waters and sediment

Understanding the microbial quality of recreational waters is critical to effectively managing human health risks. In recent years, the development of new molecular methods has provided scientists with alternatives to the use of culture-based fecal indicator methods for investigating sewage contamination in recreational waters. Before these methods can be formalized into guidelines, however, we must investigate their utility, including strengths and weaknesses in different environmental media. In this study, we investigated the decay of sewage-associated bacterial communities in water and sediment from three recreational areas in Southeast Queensland, Australia. Outdoor mesocosms with water and sediment samples from two marine and one freshwater sites were inoculated with untreated sewage and sampled on days 0, 1, 4, 8, 14, 28, and 50. Amplicon sequencing was performed on the DNA extracted from water and sediment samples, and SourceTracker was used to determine the decay of sewage-associated bacterial communities and how they change following a contamination event. No sewage-associated operational taxonomic units (OTUs) were detected in water and sediment samples after day 4; however, the bacterial communities remained changed from their background measures, prior to sewage amendment. Following untreated sewage inoculation, the mesocosm that had the most diverse starting bacterial community recovered to about 60% of its initial community composition, whereas the least diverse bacterial community only recovered to about 30% of its initial community composition. This suggests that a more diverse bacterial community may play an important role in water quality outcomes after sewage contamination events. Further investigation into potential links between bacterial communities and measures of fecal indicators, pathogens, and microbial source tracking (MST) markers is warranted and may provide insight for recreational water decision-makers.

Presence of enteric viruses, bioaccumulation and stability in Anomalocardia brasiliana clams (Gmelin, 1791)

Bivalve mollusks are filter feeders and may accumulate human pathogens in their tissues. Many studies demonstrated human diseases associated with bivalve consumption, especially oysters. Anomalocardia brasiliana clams are distributed along the Brazilian coastal area and are an exotic ingredient for some typical dishes in Brazil. Even though there are several reports describing the contamination of oysters and mussels with human pathogens, there is a lack of studies reporting contamination of A. brasiliana with human pathogens. An evaluation of natural microbiological contamination in A. brasiliana samples over a period of 18months (November 2014 to April 2016) showed that the bacteria indices were in accordance with Brazilian regulations (E. coli<230MPN and Salmonella sp. absent in 25g of meat). However, the enteric viruses evaluated were detected throughout the analysis period, with the highest result for the hepatitis A virus (HAV); followed by Rotavirus-A (RVA); Human Adenovirus (HAdV) and Norovirus GI (NoV GI). The bioaccumulation of enteric viruses by A. brasiliana during a period of 24h was performed using NoV GI and GII, HAV, RVA and HAdV as models. Interestingly the mollusk demonstrated different uptake behaviors in relation to these viruses throughout the time period. NoV GI was the most adsorbed virus after 24h. HAV concentration was <1% at 3h, but it increased to <10% at 8h, remaining unchanged until 12h, and decreasing to <3% at 24h; HAdV reached its highest concentration at 12h, being released by the animals and lowering to <3% at 24h. RVA bioaccumulation was unstable over time, reaching its highest values after 24h (<5%); NoV GII bioaccumulation remained <1%. Thermal inactivation of HAdV-2 in A. brasiliana was also evaluated. After the usual gentle cooking procedure using different times (0, 1, 1.5, 3 and 5mins), viral infectivity was evaluated using ICC-et-RT-qPCR. The temperature inside the DT remained <80°C over time and after 5min of cooking the HAdV reached a decay of 90% (1 log₁₀). The results showed a real warn to the consumers that can be exposed to infectious human viruses if they eat these clams improperly cooked. HAV was the most detected virus in these animals, which may lead to outbreaks. A. brasiliana exhibited distinct behavior in NoV GI bioaccumulation and persistence, pointing to the need for further studies about the cellular ligands used by these viruses to become attached to these clams.

Thermal Inactivation of Enteric Viruses and Bioaccumulation of Enteric Foodborne Viruses in Live Oysters (Crassostrea virginica)

Human enteric viruses are among the main causative agents of shellfish-associated outbreaks. In this study, the kinetics of viral bioaccumulation in live oysters and the heat stabilities of the predominant enteric viruses were determined both in tissue culture and in oyster tissues. A human norovirus (HuNoV) GII.4 strain, HuNoV surrogates (murine norovirus [MNV-1], Tulane virus [TV]), hepatitis A virus (HAV), and human rotavirus (RV) bioaccumulated to high titers within oyster tissues, with different patterns of bioaccumulation for the different viruses. We tested the thermal stability of each virus at 62, 72, and 80°C in culture medium. The viruses can be ranked from the most heat resistant to the least stable as follows: HAV, RV, TV, MNV-1. In addition, we found that oyster tissues provided protection to the viruses during heat treatment. To decipher the mechanism underlying viral inactivation by heat, purified TV was treated at 80°C for increasing time intervals. It was found that the integrity of the viral capsid was disrupted, whereas viral genomic RNA remained intact. Interestingly, heat treatment leading to complete loss of TV infectivity was not sufficient to completely disrupt the receptor binding activity of TV, as determined by the porcine gastric mucin-magnetic bead binding assay. Similarly, HuNoV virus-like particles (VLPs) and a HuNoV GII.4 strain retained some receptor binding ability following heat treatment. Although foodborne viruses have variable heat stability, 80°C for >6 min was sufficient to completely inactivate enteric viruses in oysters, with the exception of HAV.

Effect of UV light on the inactivation of recombinant human adenovirus and murine norovirus seeded in seawater in shellfish depuration tanks

Shellfish depuration is a process that aims to eliminate pathogens from mollusk tissues. Seawater disinfection during the depuration process is important and ultraviolet (UV) light treatment is the most used method worldwide. Viral models are usually employed as surrogates of fastidious viruses in viability studies. The aim of this study was to employ methods based on green fluorescent protein (GFP) fluorescence and plaque forming units to detect, respectively, recombinant adenovirus (rAdV-GFP) and murine norovirus (MNV) artificially seeded in environmental matrices. These assays were applied to assess the inactivation of rAdV-GFP and MNV in seawater in recirculation shellfish depuration tanks with and without UV light treatment. Kinetics of rAdV GFP-expression was previously measured by UV-spectrophotometer. Flow cytometry (FC), fluorescence microscopy (FM), and plaque assay were used to determine virus titer and detection limits. The influence of the environmental matrix on the performance of the methods was prior determined using either drinking water or filtered seawater seeded with rAdV-GFP. Disinfection of seeded seawater was evaluated with and without UV treatment. The time of 24-h post-infection was established as ideal for fluorescence detection on rAdV-GFP infected cells. FC showed lower sensitivity, when compared to FM, which was similar to plaque assay. Seawater disinfection on depuration tanks was promising and rAdV-GFP declined 99.99 % after 24 and 48 h with and without UV treatment, respectively. MNV was completely inactivated after 24 h in both treatments. As conclusion, the depuration tanks were effective to inactivate rAdV-GFP and MNV and the UV disinfection treatment accelerated the process.