Food borne virus detection
By Suzanne Jordan - 13th June 2014
Two major issues with foodborne virus detection are that viruses need a host cell in which to replicate (they do not grow on food), and that viral RNA or DNA, even if present, may or may not be infective. Over recent years there has been an increase in the level of food borne illness associated with food contaminated with viruses. Of significant importance are hepatits A (HAV) and norovirus (NoV). Virus related foodborne illness is becoming a major issue, as highlighted by the recent outbreaks of HAV in Italy and NoV in Germany. Epidemiological data show that NoV is a major cause of infectious intestinal disease in the UK (and the world). Over the last 10 years there has been a significant increase in the number of reported cases of NoV in England and Wales, with nearly 11,000 recorded in 2012. The route of NoV infection is known to be through one of two routes: person-to-person spread and the consumption of contaminated food, although the percentage contribution of these two vectors in outbreaks is not always known. Evidence has shown, however, that large outbreaks of NoV and HAV have occurred due to contaminated foods, so manufacturers may want to check that process controls that they have in place to control viruses are effective. An ACMSF report on food borne viruses in the food chain has been open for consultation recently and this document could influence what controls are deemed necessary.
One of the characterising features of viruses is that they require host cells for replication. This creates unique challenges for the detection of foodborne viruses which are reliant on molecular based techniques to provide sensitive analysis. An ISO technical standard has been published which details the method to be followed for the detection of HAV and NoV in food products. It uses a real time reverse transcription polymerase chain reaction (real time RT-PCR) assay for detection and the protocol has 3 distinct steps:
Matrix specific virus recovery is required to cope with the complexity of the matrices being analysed and the potential low level of contamination of
virus particles in the sample.
RNA extraction is required to reduce the potential impact of PCR inhibitors within the sample that may prevent the detection of virus particles. The extraction process involves the purification of the RNA using silica coated magnetic beads. At the end of the wash steps, the purified viral RNA is released from the beads into an elution buffer prior to PCR analysis.
Results generated using this method give an indication of the presence of virus particles in samples, although it cannot provide information on the potential for their infectivity. Further development is required to create assays that provide information on the presence of infective viruses in foods and food related environments. This assay could be used in conjunction with effective controls to monitor food safety in relation to virus contamination.
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