Viruses transmitted through the food chain: a review of the latest developments.

The emergence of severe acute respiratory syndrome (SARS), Nipah virus and H5N1 has sparked fears of food-borne dissemination of viruses, resulting in an increased focus on microbiological food safety. Norovirus (NoV) and hepatitis A virus (HAV) have been recognized as priorities based on their illness burden, and as models for prevention studies. In addition, hepatitis E virus is considered an emerging food-borne pathogen. Systematic surveillance for food-borne viral diseases, where present, has to deal with underreporting, with available data biased towards developed countries, making true estimates of the burden of illness challenging. Nevertheless, food-borne viral outbreaks are often reported, whereas current measures undertaken by food safety management organizations are focused primarily on bacterial contamination and are insufficient for viruses in food. There has been a shift towards molecular techniques for the diagnosis and detection of viruses in food, but a definite link to food is still hard to establish owing to the low levels of viruses in foods. Moreover, multiple strains may be involved in sewagecontaminated foods, with the risk of recombination and development of novel strains after ingestion. To enable monitoring of food and food safety, sensitive routine methods are needed, and methods for detection of NoV and HAV in risk foods (shellfish, soft fruit and leafy greens) are currently validated. Norovirus cannot be cultured, but the murine NoV may be a surrogate for studying NoV survival. In all, significant progress has been made in understanding food-borne viral infections, but clear data gaps still exist and should be the focus of future research.