Saliva Identified as a New Transmission Route for Enterovirus

Introduction: Enteroviruses, such as norovirus and rotavirus, can be spread by eating some foods or liquids that have been contaminated with feces containing the virus. But recently, some scientists have confirmed that this type of enterovirus also has a way of saliva transmission.
Scientists at the National Institutes of Health have discovered that a type of enterovirus that causes severe diarrheal disease can grow in the salivary glands of mice and spread through saliva. The findings suggest a new route of transmission for these deadly common viruses that afflict billions of people around the world each year.
The ability of these enteroviruses to spread through saliva suggests that coughing, talking, sneezing, sharing food and utensils, and even kissing have the potential to spread the virus. But this has yet to be confirmed in humans.
The research, led by the NIH-affiliated National Heart, Lung, and Blood Institute (NHLBI), may lead to better ways to prevent, diagnose and treat diseases caused by these viruses, and possibly even save a lot of lives. The findings were published in the journal Nature. https://www.nature.com/articles/s41586-022-04895-8
Researchers know that enteroviruses, such as norovirus and rotavirus, can be spread by eating some foods or liquids that have been contaminated with virus-containing feces. We used to think that enteroviruses skip the salivary glands, target only the gut, and are subsequently excreted in the feces. Although some scientists have suspected that there may be another transmission route, this theory has so far not been tested.
Now, researchers need to show that it is possible for enteroviruses to spread through saliva in humans. If confirmed, the researchers say, this route of transmission may also be found to be even more common than the traditional route of transmission.
Altan-Bonnet, who has studied enteroviruses for many years, said the discovery was entirely accidental. Her team has been experimenting with enteroviruses in young mice. The immature digestive and immune systems of young mice make them susceptible to infection, making them the animal model of choice for research.
In the experiment, the researchers fed a group of newborn mice less than 10 days old with norovirus and rotavirus. They then returned the pups to their cages and had them suck on breast milk from their virus-free mothers. Just one day later, team member Dr. Sourish Ghosh noticed something unusual: a surge in IgA antibodies, an important disease-fighting component, in the guts of young mice. This is rather surprising, since the immune systems of young mice are immature and cannot produce their own antibodies at this stage.
In addition, Ghosh noticed that the virus replicated abundantly in the mother’s breast tissue (the milk duct cells). When Ghosh collected breast milk from the udders of rat mothers, he found that the timing and levels of IgA surges in breast milk coincided with the timing and levels of IgA surges in the guts of pups. Infections in the mother’s breast appeared to boost the production of IgA antibodies in breast milk, which ultimately helped clear the infection in pups, the researchers said.
To understand how the virus initially entered the mother’s breast tissue, the researchers conducted an additional experiment and found that the mouse pups did not transmit the virus to their mothers by the traditional route — through contaminated feces Stay in a shared living space for their mother to ingest. They set out to investigate whether the virus in the mother’s breast tissue might have come from the pups’ saliva and somehow spread during lactation.
To test this conjecture, Ghosh collected saliva samples and salivary glands from young mice and found that the salivary glands replicated the viruses at very high levels and shed the virus in large quantities into their saliva. This additional experiment quickly confirmed the saliva theory: breastfeeding causes virus transmission between mother and baby.
Senior author Nihal Altan-Bonnet, Ph.D., director of NHLBI’s Laboratory of Host-Pathogen Dynamics, said: “This is an entirely new field because we previously thought these viruses could only grow in the gut. Saliva transmission of enteroviruses is something we didn’t know yet. Another level of transmission. We need to rethink how these viruses are transmitted and diagnosed, but most importantly, how to slow their spread.”