Bad news: Raw oysters harbor and spread the norovirus

 

This is some bad news for people who like to eat raw oysters: The mollusks have a knack for harboring and spreading the stomach bug known as the norovirus.

According to a new study published in Applied and Environmental Microbiology, researchers found that oysters contain the norovirus, and a genetic analysis revealed norovirus outbreaks can be traced back to the coastal regions where oysters are cultivated.

“More than 80 percent of human norovirus genotypes were detected in oyster samples or oyster-related outbreaks,” study author Yongjie Wang, from Shanghai Ocean University, said in a news release. “The results highlight oysters’ important role in the persistence of norovirus in the environment, and its transmission to humans, and they demonstrate the need for surveillance of human norovirus in oyster samples.”

In the study, the researchers obtained all oyster-related norovirus genetic sequences entered into the National Center for Biotechnology’s GenBank data repository and the Noronet outbreak repository from 1983 through 2014. The team then executed genotyping and phylogenic analyses, and traced the norovirus’ genetic diversity and geographic circulation over time.

In previous study, the researchers discovered that 90 percent of human norovirus sequences in China originated from coastal regions. The current study exhibited the same pattern all over the world, with the exception of tropical locations, from which sequences are missing.

The discovery that oysters are vectors and reservoirs for norovirus spread is likely due to their presence in coastal waters, which are regularly toxified by human waste, according to Wang. Previous studies have indicated that noroviruses can persevere for weeks in oyster tissues, and commercial attempts to expunge them are typically ineffective.

So can I still eat oysters?

Norovirus brings about stomach discomfort, diarrhea, queasiness, and vomiting. The virus is highly contagious, and infects greater than 6 percent of the US population each year, causing around 20 million cases, 56,000 to 71,000 hospitalizations, and 570 to 800 deaths, based on Centers for Disease Control and Prevention data. Just touching a contaminated surface can lead to the virus being contracted.

Wang said people who consume shellfish should consume them fully cooked, rather than raw. He also advised advancement of a dependable method for finding noroviruses in oysters, and a global oyster-related norovirus outbreak surveillance network.

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