For the first time researchers have grown a human norovirus in a cell culture dish, taking a step toward developing medications to treat the stomach bug that strikes millions of people every year in schools, hotels, and cruise ships.
Noroviruses are intestinal viruses that cause violent vomiting and diarrhea. In the U.S. alone, human noroviruses cause 19 million to 21 million cases of illness every year, and contribute to up to 71,000 hospitalizations. Noroviruses are also usually resistant to many common disinfectants, so a surface may still contain enough virus to infect a person even after it is cleaned.
Since it was discovered in 1972, the biggest hurdle in doing norovirus research has been the inability to culture the human viruses in a cell culture dish, said Stephanie Karst, associate professor in the molecular genetics and microbiology department at University of Florida College of Medicine.
“That complicates every aspect of research. We can’t study how it replicates, we can’t test therapeutics, and we can’t generate live virus vaccines,” she added.
All that, however, is in the process of changing as new research demonstrates that the virus targets B cells, a type of white blood cell common in the intestine. Previous research had speculated that noroviruses primarily target intestinal epithelial cells, which line the intestine and protect it from pathogens.
“That’s a big surprise,” Karst said. “You would think that any virus that’s going to target the intestine would instead target the intestinal epithelial cells because that’s the first cell the virus is going to encounter.”
Researchers were also surprised to find that bacteria present in the body’s gut flora, also known as commensal bacteria, helped the human norovirus infect B cells. Scientists have long known that noroviruses need a particular kind of carbohydrate to infect cells, but this was the first time they were able to pinpoint anything in particular.
“What we’ve shown is that noroviruses attach to that carbohydrate expressed on commensal bacteria, and that this interaction stimulates viral infection of the B cell,” Karst says. “This is a really exciting, emerging theme. A variety of intestinal viruses seem to exploit the bacteria that are present in our intestines all the time. These viral infections are enhanced by the presence of bacteria in the gut.”
“Ultimately,” she continued, “this system should open up new avenues for norovirus vaccine and antiviral drug development.”
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