Norovirus contamination found in oysters worldwide

Abstract

Noroviruses (Norwalk-like viruses) are recognized as major causes of acute gastroenteritis worldwide. Outbreaks of norovirus gastroenteritis are often associated with consumption of oysters. In this study, oysters imported into Hong Kong from 11 countries over a 3-year period were screened by RT-PCR. Overall, 53 out of 507 (10.5%) samples were positive for norovirus-RNA, and a wide variety of strains were found. Two novel genetic clusters were detected, which could indicate novel human or animal norovirus strains. However, whether these two new clusters are of human or animal origin is not known. Thirteen outbreaks, in which oysters were implicated as the source of infection were investigated: Norovirus RNA sequences could be detected in oysters from six outbreaks, but only in one outbreak the strains isolated from patients and oysters matched (>98% homology). Therefore, RT-PCR was of use in detecting norovirus contamination of oysters implicated in an outbreak, but was less useful in demonstrating an actual molecular epidemiological link with human cases. It was shown that contamination by noroviruses could be demonstrated in oysters worldwide, and therefore oysters may serve as an important vehicle for introducing novel norovirus strains.

Binding of Virus-Like Particles of Norwalk Virus to Romaine Lettuce Veins

“…Therefore, the RE was treated by being boiled or with 3A). Binding of rNVLP to RE, however, was affected by both KIO 4 and by boiling RE by a small, but statistically significant, amount. KIO 4 treatment resulted in a minor increase in binding (8.9 Ϯ 4.0%) relative to untreated RE (P Ͻ 0.05).…”

“…The most common and best characterized route of infection is through the consumption of oysters (4), which are contaminated directly at the source of harvest. Histo-blood group antigens (HBGA), identified as receptors on human gastrointestinal cells to which NoV virions bind (10,11,19), are also present on the surfaces of oyster gastrointestinal cells (25).…”

Binding of Human GII.4 Norovirus Virus-Like Particles to Carbohydrates of Romaine Lettuce Leaf Cell Wall Materials

“…Recently, GII.4 NoVs have been found to bind to the digestive tracts of oysters through carbohydrate structures that are similar to the A-type HBGA (25,40). The specific binding allows the virus to concentrate inside the digestive tract and resist removal through depuration, which might explain why NoV outbreaks frequently occur in shellfish (9,26). A similar situation could potentially occur on cut edges of shredded or damaged lettuce leaves, since NoV VLPs not only adsorb or entrap inside open cuts but also could bind specifically to exposed cell wall carbohydrates, as we showed here.…”

Molecular Epidemiology of Oyster-Related Human Noroviruses and Their Global Genetic Diversity and Temporal-Geographical Distribution from 1983 to 2014

“…Furthermore, because oysters typically grow in coastal water potentially contaminated by human activities (18) and are often consumed half-cooked or raw (12,19), this food presents a high risk for viral infections and is frequently involved in NoV outbreaks (20,21). NoVs appear to be able to persist in oyster tissues for weeks and cannot be effectively removed during commercial depuration (22)(23)(24).…”