Norovirus and other “stomach bugs” can spread throughout saliva

A class of viruses known to cause severe diarrheal disease, including the virus known for its widespread outbreaks on cruise ships, can grow in the salivary glands of mice and spread through saliva. Discovered by scientists at the National Institutes of Health. Research results show that there are new transmission routes for these common viruses that can be fatal and afflict billions of people around the world each year.

The transmission of these so-called intestinal viruses through saliva suggests that coughing, talking, sneezing, sharing food and tools, and even kissing can all spread the virus. New discoveries still need to be confirmed in human studies.

Findings published in Nature may lead to better ways to prevent, diagnose, and treat diseases caused by these viruses, which can save lives. This study was led by the National Heart, Lung and Blood Institute (NHLBI), which is part of the NIH.

Researchers have long known that intestinal viruses such as norovirus and rotavirus can spread by eating foods and liquids contaminated with feces containing these viruses. The intestinal virus was thought to bypass the salivary glands, target the intestine, and later be excreted from the faeces. This theory has been rarely tested, although some scientists suspect that there may be another pathway of transmission.

Now, researchers need to confirm that salivary infections of the intestinal virus are possible in humans. Researchers said that if they found out, they might find that this route of transmission is even more common than the traditional route. They said such findings may help explain why numerous intestinal viral infections worldwide each year cannot adequately explain fecal contamination as the only route of transmission.

“This is a completely new area because these viruses were thought to grow only in the gut,” said senior author Dr. Nihal Altan-Bonnet, head of the NHLBI’s Host-pathogen Interaction Laboratory. .. “Saliva infections of intestinal viruses are another layer of infection that we did not know about. This is how these viruses are transmitted, how they are diagnosed, and most importantly, how. It’s a whole new way of thinking about how the spread will be mitigated. ”

Altan-Bonnet, who has been studying intestinal viruses for many years, said the discovery was entirely coincidental. Her team was experimenting with intestinal virus in infant mice. These animal models are the best animal models for studying these infectious diseases because of the immature digestive and immune systems.

In the current study, researchers fed a group of newborn mice <10 days old with either norovirus or rotavirus. The mouse pups were then returned to their cages to feed their mother, who was initially virus-free. Only a day later, NHLBI researcher and research co-author Sourish Ghosh, Ph.D., one of the Altan-Bonnet team members, noticed something changed. Mouse puppies showed a surge in IgA antibodies (a component that fights important diseases) in the intestine. This was surprising given that the immune system of the mouse offspring was immature and was not expected to produce their own antibodies at this stage.

Gauche also noticed another anomaly. The virus replicated at high levels in the mother’s breast tissue (ductal cells). When Gauche collected milk from the mother’s milk in mice, it was found that the timing and level of IgA surge in the mother’s milk reflected the timing and level of IgA surge in the puppy’s intestine. The mother’s breast infection appeared to have stimulated the production of IgA antibodies that fight the virus in breast milk, which ultimately helped clear the puppy’s infection, the researchers said.

Researchers who wanted to know how the virus invaded the mother’s breast tissue in the first place conducted additional experiments and found that mouse puppies traditionally left contaminated feces in a shared life. It turns out that the route did not infect the mother with the virus. Space for mothers to ingest. At that time, the researchers suspected that the virus in the mother’s breast tissue originated in the saliva of the infected puppy and somehow spread during lactation.

To test the theory, Ghosh collected saliva samples and salivary glands from mouse puppies and found that the salivary glands replicate these viruses at very high levels and excrete large amounts of the virus into saliva. .. Additional experiments quickly confirmed saliva theory. Breastfeeding caused both mother-to-child and child-to-mother viral transmissions.

reference: Ghosh S, Kumar M, Santiana M, and other intestinal viruses replicate in the salivary glands and are transmitted through saliva. Nature.. Published online June 29, 2022, 1-6. Doi:10.1038 / s41586-022-04895-8

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