By Dr. Joseph D. Lim
A class of viruses known to cause severe diarrhea can grow in the salivary glands of mice and spread through their saliva.
This was discovered by scientists at the U.S. National Institutes of Health (NIH).
Their findings show that a new route of transmission exists for these common viruses, which afflict billions of people each year worldwide and can be deadly.
Coughing, talking, sneezing, sharing food and utensils — and even kissing all have the potential for spreading viruses.
That is, through saliva, according to new findings published in the journal Nature that still need to be confirmed in human studies.
The findings about the enteric (intestinal) viruses could lead to better ways to prevent, diagnose and treat diseases caused by these viruses, potentially saving lives, according to the NIH.
The study was led by the National Heart, Lung and Blood Institute (NHLBI), a part of NIH.
And here we quote the NIH:
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. Although some scientists have suspected there may be another route of transmission, this theory remained largely untested until now.
Researchers will need to confirm that salivary transmission of enteric viruses is possible in humans. If they find that it is, the researchers said, they may also discover that this route of transmission is even more common than the conventional route.
A finding such as that could help explain, they said, why the high number of enteric virus infections each year worldwide fails to adequately account for fecal contamination as the sole transmission route.
“This is completely new territory because these viruses were thought to only grow in the intestines,” said senior author Nihal Altan-Bonnet, Ph.D., Chief of the Laboratory of Host-Pathogen Dynamics at the NHLBI.
“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,” she said.
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, one of Dr. Altan-Bonnet’s team members, NHLBI researcher and study co-author Sourish Ghosh, Ph.D., noticed something unusual.
The guts of the mouse pups showed a surge in IgA antibodies — important disease-fighting components. 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.
Dr. Ghosh also noticed other unusual things: The viruses were replicating in the mothers’ breast tissue (milk duct cells) at high levels.
When Dr. Ghosh collected milk from the breasts of the mouse mothers, he found that the timing and levels of the IgA surge in the mothers’ milk mirrored the timing and levels of the IgA surge in the guts of their pups.
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.
Eager to know how the viruses got into the mothers’ breast tissue in the first place, the researchers conducted additional experiments and 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 the researchers decided to see whether the viruses in the mothers’ breast tissue might have come from the saliva of the infected pups and somehow spread during breastfeeding.
They found that the salivary glands from the mouse pups were replicating these viruses at very high levels and shedding the viruses into the saliva in large amounts.
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Dr. Joseph D. Lim, Ed. D., is the former Associate Dean of the College of Dentistry, University of the East; former Dean, College of Dentistry, National University; Past President and Honorary Fellow of the Asian Oral Implant Academy; Honorary Fellow of the Japan College of Oral Implantologists; Honorary Life Member of the Thai Association of Dental Implantology; and Founding Chairman of the Philippine College of Oral Implantologists. For questions on dental health, e-mail jdlim2008@gmail.com or text 0917-8591515.
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Dr. Kenneth Lester Lim, BS-MMG, DDM, MSc-OI, graduated Doctor of Dental Medicine, University of the Philippines, College of Dentistry, Manila, 2011; Bachelor of Science in Marketing Management, De La Salle University, Manila, 2002; and Master of Science (MSc.) in Oral Implantology, Goethe University, Frankfurt, Germany, 2019. He is an Associate Professor; Fellow, International Congress of Oral Implantologists; Member, American Academy of Implant Dentistry and Fellow, Philippine College of Oral Implantologists. For questions on dental health, e-mail limdentalcenter@gmail.com./WDJ