Research Shows Norovirus, Other ‘Stomach Bugs,’ Can Spread Through Saliva

Enteric viruses, which cause severe diarrheal diseases, afflict billions of people each year worldwide and can be deadly. NIH scientists have discovered that this class of viruses can grow in the salivary glands of mice and spread through their saliva. The findings show that a new route of transmission exists for these common viruses that include noroviruses—famous for widespread outbreaks on cruise ships—and rotaviruses.

The transmission of enteric viruses through saliva suggests that coughing, talking, sneezing, sharing food and utensils and even kissing all have the potential for spreading the viruses. If the new findings are confirmed in human studies, they could lead to better ways to prevent, diagnose and treat enteric viruses, potentially saving lives. Results from the NHLBI-led study appear in Nature. 

Enteric viruses can spread by consuming food or liquids contaminated with fecal matter containing these viruses, exiting later through feces. 

“This is completely new territory because these viruses were thought to only grow in the intestines,” said Dr. Nihal Altan-Bonnet, chief of NHLBI’s Laboratory of Host-Pathogen Dynamics. 

The discovery was serendipitous. Altan-Bonnet’s team had been conducting experiments with enteric viruses in infant mice, who were fed either norovirus or rotavirus. The mouse pups were then allowed to suckle their mothers, who were initially virus-free. 

But after a day, the mouse pups showed a surge in IgA antibodies, important disease-fighting components, in their guts. This was surprising considering that the immune systems of the mouse pups were immature and not expected to make their own antibodies at this stage.

Additionally, the viruses were replicating in the mothers’ breast tissue (milk duct cells) at high levels. It seemed the infection in the mothers’ breasts had boosted the production of virus-fighting IgA antibodies in their breast milk, which ultimately helped clear the infection in their pups, the researchers said.

The researchers found that the mouse pups had not transmitted the viruses to their mothers through the conventional route—by leaving contaminated feces in a shared living space for their mothers to ingest. That’s when they began testing whether the virus somehow spread during breastfeeding. Further testing confirmed the mouse pups’ salivary glands were replicating these viruses at very high levels and that suckling had caused mother-to-pup and pup-to-mother viral transmission.