Oysters Are Norovirus Factories, Say Experts

Norovirus is an infamous illness. Ruining cruises and restaurant outings alike, norovirus infections are responsible for more than 20 percent of all reported "food poisoning" cases worldwide. Now, new research has determined that raw oysters not only transmit the virus, but also harbor it.

That's at least according to a study recently published in the journal Applied and Environmental Microbiology.

The study details how "more than 80 percent of human norovirus genotypes were detected in oyster samples or oyster-related outbreaks," Yongjie Wang, a professor in the College of Food Science and Technology, Shanghai Ocean University, Shanghai, China, explained in an emailed statement.

Specifically, Wang and his colleagues closely examined all oyster-related norovirus sequences archived between 1983-2014 in a pair of international health and outbreak databases. Earlier studies had found that 90 percent of human norovirus sequences in China came from coastal regions, but this new work shows that this holds true across the world, with oysters largely to blame. (Scroll to read on...)

It's no secret that you risk an upset stomach when eating raw or undercooked oysters, but the exact cause had always been hazy. Wang's work found that oysters not only serve a vectors for norovirus, transferring it to humans, but also can serve as virus reservoirs, allowing the infectious disease to build and mature into a virulent strain.

What's more, oysters are commonly contaminated by human waste, meaning the virus often finds refuge once again in oyster tissue after being unceremoniously 'expelled' by a human victim's body. Previous research suggests that noroviruses can persist for weeks in oyster tissues, and commercial depuration fails to expunge them.

Knowing this, Wang advises that seafood lovers should eschew eating raw oysters in favor of cooked varieties, such as found in many popular pasta dishes. The hope now, is that with a better understanding of how norovirus finds refuge in oysters, a "worldwide oyster-related norovirus outbreak surveillance network" can be developed to keep consumers safe.

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