A class of viruses known to cause severe diarrhoeal diseases can grow in the salivary glands of mice and spread through their saliva, scientists have discovered.
The findings by a team at the US National Institutes of Health (NIH) show that a new route of transmission exists for these common viruses, such as norovirus, which afflict billions of people each year worldwide and can be deadly.
The transmission of these so-called enteric viruses through saliva suggests that coughing, talking, sneezing, sharing food and utensils, and even kissing all have the potential for spreading the viruses.
However, this still needs to be confirmed in human studies.
The findings, which appear in the journal Nature, could lead to better ways to prevent, diagnose, and treat diseases caused by these viruses, potentially saving lives.
“This is completely new territory because these viruses were thought to only grow in the intestines,” said senior author Nihal Altan-Bonnet, chief of the Laboratory of Host-Pathogen Dynamics at the National Heart, Lung, and Blood Institute (NHLBI), part of the NIH.
“Salivary transmission of enteric viruses is another layer of transmission we didn’t know about. It is an entirely new way of thinking about how these viruses can transmit, how they can be diagnosed, and, most importantly, how their spread might be mitigated,” Altan-Bonnet said.
Researchers have known for some time that enteric viruses, such as noroviruses and rotaviruses, can spread by eating food or drinking liquids contaminated with fecal matter containing these viruses.
Enteric viruses were thought to bypass the salivary gland and target the intestines, exiting later through feces.
For the study, the researchers fed a group of newborn mice that were less than 10 days old with either norovirus or rotavirus.
The mouse pups were then returned to cages and allowed to suckle their mothers, who were initially virus-free.
After just 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.
Further, the viruses were found 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 team found that instead of the conventional route –A contaminated feces in a shared living space, the viruses in the mothers’ breast tissue came from the saliva of the infected pups and spread during breastfeeding.