The contagious norovirus is the most common cause of acute gastroenteritis in the US. At present, there is no form of medicine able to treat it, due to scientists being unable to cultivate the virus in human cells in order to test medications. Information in a new study could change this, however.
Researchers from the University of Florida Health have identified the cells that the virus targets in the intestine, along with a stimulatory factor in norovirus infection.
The discovery, published in the journal Science, should enable them to grow the virus in human cells.
“The biggest hurdle to doing norovirus research for its entire history – it was discovered in 1972 – has been that we can’t culture the human viruses in a cell culture dish,” says study author Stephanie Karst. “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.”
As well as causing acute gastroenteritis, norovirus is also the most common cause of foodborne-disease outbreaks in the US. The virus can be easily transmitted through contact with contaminated food and water, contaminated surfaces or other infected people.
The Centers for Disease Control and Prevention (CDC) report that norovirus is responsible for around 19-21 million illnesses and is a contributing factor to 56,000-71,000 hospitalizations and 570-800 deaths every year.
Unfortunately, noroviruses are resistant to many common disinfectants, and as minimal contact can be enough to spread the virus, a contaminated surface that has been cleaned is still capable of spreading infection. Diligent hygiene is essential to prevent the transmission of the virus.
Researchers had previously thought that noroviruses would primarily target the protective cells lining the intestine – the epithelial cells – as these would be the first cells that the virus would come into contact with.
- Hands should be washed carefully with soap and water, particularly after using the toilet or before food preparation
- Fruits and vegetables should be rinsed, and shellfish should be cooked thoroughly before consumption
- After diarrhea or vomiting, contaminated surfaces should be cleaned and disinfected immediately.
However, previous research from Karst involving mice led the researchers to examine B cells – a common form of blood cell – and in the new study, they were found to be the primary targets of the virus. Karst describes the finding as “a big surprise.”
The study authors also discovered that the bacteria present in the gut, referred to as commensal bacteria, assisted in the norovirus’ infection of the B cells. Scientists have been aware that noroviruses require a form of carbohydrate in order to infect cells, but Karst and the team were surprised to find it was a carbohydrate in the gut bacteria to which the virus attached.
When oral antibiotics were used to deplete the levels of commensal bacteria in mice with norovirus, norovirus replication was also found to reduce.
“This is a really exciting, emerging theme,” says Karst. “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.”
It is likely that previous attempts to culture human noroviruses failed due to the absence of these stimulatory carbohydrate molecules, write the authors. “Ultimately, this system should open up new avenues for norovirus vaccine and antiviral drug development,” says Karst.
Recently, Medical News Today reported on a trial drug being tested against Ebola and influenza that had been found to successfully treat norovirus in mice by speeding up mutation.