The occurrence of enteric viruses in shellfish
A review of: Suffredini, E., Corrain, C., Arcangeli, G., Fasolato, L., Manfrin, A., Rossetti, E., Biazzi, E., (2008), Occurrence of enteric viruses in shellfish and relation to climatic-environmental factors, Applied Microbiology, 47(5):467-474
Shellfish are considered to be potential vectors of foodborne diseases, due to their accumulation of pathogenic microorganisms through filter-feeding. Norovirus (NoV) is an enteric virus that has been linked to shellfish-associated disease outbreaks and is responsible for 60-80% of human gastroenteritis outbreaks. Similarly, shellfish are linked to the transmission of hepatitis A virus (HAV), and its consumption has been reported in 69% of HAV infected patients. In Italy, there have been numerous cases of these diseases related to seafood consumption registered in several cities.
It has been established that climate has direct and indirect effects on the occurrence of enteric viruses. For example, high precipitation can cause flooding and sewage runoff which are key factors in contamination of coastal water and shellfish harvesting areas.
The aim of this study was to assess the prevalence of HAV and NoV in shellfish harvested in a specific national production area, the deltic area of the river Po (North Italy). They also looked at the effect that environmental factors have on viral contamination in the production area.
A survey was carried out for 1 year on samples of shellfish (mussels and clams), taken every 15days from two areas, A (sea area) and B (lagoon area). Environmental parameters such as temperature, pH and salinity were noted as well as bacteriological analysis (for E.coli and Salmonella) and virological analysis (for NoV and HAV), using various PCR methods.
The results showed no significant differences in environmental paramaters in the two areas, with some predictable fluctuations due to seasonal variations. No Salmonella was detected and E.coli numbers were always below legislation limits. There was also no HAV found in both areas but NoV was detected in 10 of the 120 samples, all from area B. NoV was also present in samples ranging throughout the sampling period, with the majority of positive samples in spring and summer. This led the researchers to conclude that a definite association between NoV clinical cases arising during the winter period and shellfish cannot be established.
They also noted that the increase in viral contamination could be in relation to the flow of the tributary river, which could transport further viruses into the harvesting areas and moreover mixes and lifts the sediment at the bottom of the lagoon where viruses can deposit and survive for long periods.
The study highlights the importance of accurate classification of harvesting areas in assuring the safety of shellfish for direct consumption and is useful in helping to establish suitable prevention techniques, especially after meteorological events.
4 comments:
Whilst posting this, I noticed the title said, the occurrence in relation to environmental and climatic effects. They've noted the affects of the river flow, however their sampling method did not allow them to make any links between rain fall and contamination. Perhaps more focus should be put on this next time as heavy rainfall and other events could have big impacts on the spread of viruses and bacteria in the water column. They should establish whether these two areas are particularly at risk of the affects of heavy rainfall, as it would impact on the contamination of the shellfish.
Hi Jelena,
Nice post, I have been interested in shellfish poisoning but I always think about the link with harmful algal blooms, I can imagine this being of great concern to the shellfish farmers as they will also suffer economically, maybe more stringent analysis of river tributaries around stormy/ bad weather could help prevent cases getting as far as affecting humans directly from consumption.
Hey Jelena,
Interesting review. You mentioned the NoV and HaV virus infection of shellfish arises from flooding and sewage run offs etc. Does this mean this infection is terrestrial in origin and is a zoonotic disease in reverse? I think they call it an anthroponosis or reverse zoonosis.
Hi Dan,
yes I agree, monitoring of weather events and the river tributaries would help to understand the spread of the virus and how it could be prevented or avoided from the production areas. Mario, in answer to your question, from what I understand it is transmitted through food or water that is contaminated by human faeces, so yes I believe it is reverse zoonoses, however I am unable to find much about its origin, so it could well be of zoonotic origin that has been transmitted to humans and then spread from human to human transmission.
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