November 6, 2014 § Leave a comment
Now, in a paper in the journal Science, researchers describe a way to culture human norovirus. They also discovered that an intestinal bacterium helps the virus with the infection.
“Although the mouse noroviruses were easily cultured, the inability to culture human noroviruses has always been the major roadblock to studying this clinically important family of viruses,” explains Stephanie Karst at the University of Florida, who led the study.
Work in mice had shown that the virus infects B cells in the immune system. So Karst and colleagues decided to see if they could co-culture the human norovirus with human B cells.
The source of the virus was stool samples from patients with the infection. Researchers have always used stools teeming with the virus to collect the pathogen. But they usually filtered the samples to remove the bacteria with the view that the bacteria were contaminants in the viral prep.
This time, Karst’s team decided to skip the filtering step and directly add the stool samples to cultured human B cells. Then they carried out real-time PCR to detect the virus in the culture. They found that the virus was able to replicate in the culture, albeit modestly.
Work with the mouse norovirus also had hinted that the pathogen required a helping hand from another microorganism. Karst says they had noticed that the virus was less capable of replicating in mice whose gut flora was depleted.
“To test whether bacteria also enhanced human norovirus infection of cultured B cells, we applied either unfiltered stool from a virus-infected person, containing virus and intestinal bacteria, or filtered stool,” says Karst. “We observed that removal of bacteria reduced viral infection of B cells.”
Karst says that the human norovirus culture system is a major advance in the field. “This system can now be used to test the effectiveness of potential antiviral compounds in blocking norovirus replication and the ability of virus-specific antibodies to neutralize viral infection of B cells,” she notes. However, she points out that the culture system requires additional tinkering to improve the infection rate of the human B cells by the virus.
The investigators are also curious which bacteria in the human gut help the norovirus infect B cells and exactly how the bacteria provide the assistance during the infection.