Summary It has long been accepted that enteric viruses such as norovirus, rotavirus, and astrovirus spread in the population through fecal-oral transmission : viruses are shed in a host’s feces and enter the oral cavity of a host. another, bypassing the salivary glands (SG) and reaching the intestines to replicate, be eliminated in the feces and repeat the transmission cycle. However, there are viruses (for example, rabies ) that infect SGs, making the oral cavity a site of replication and saliva a conduit of transmission . Here we report that enteric viruses productively and persistently infect SGs, reaching titers comparable to those in the intestines. We demonstrate that enteric viruses are released in saliva , identifying a second route of viral transmission. This is particularly significant for infected infants, whose saliva directly transmits enteric viruses to their mothers’ mammary glands through reflux during breastfeeding. This bypasses the conventional gut-mammary axis pathway and leads to a rapid increase in breast milk secretory IgA antibodies . Finally, we show that SG-derived spheroids and cell lines can replicate and propagate enteric viruses , generating a scalable and manageable production system. Taken together, our research uncovers a new transmission route for enteric viruses with implications for therapy, diagnosis and, most importantly, sanitation measures to prevent spread through saliva. |
Saliva forms the first line of defense against many pathogens that enter orally and can reflect the clinical status of an individual. Saliva tests are commonly used to diagnose several viruses that infect SGs, such as Epstein-Barr virus, rabies virus, herpes simplex virus, and severe acute respiratory syndrome coronaviruses 1 and 2. Genomic RNA from norovirus, rotavirus, and astrovirus has been frequently detected in the saliva of symptomatic and asymptomatic individuals.
These observations were interpreted as intestinal contaminants because these viruses are believed to be transmitted primarily through the fecal-oral route through ingestion of contaminated food and water and replicate productively in the intestines.
Breastfeeding transmits enteric viruses to mothers
Newborn mouse pups (less than 10 days old) are excellent models for studying enteric infections because their immature digestive tracts and immune systems make them susceptible to viruses. Indeed, intestinal enteric infections were easily detectable when pups were orally inoculated with murine norovirus 1 (MNV-1) or rotavirus (epizootic diarrhea of lactating mice (EDIM)) and replication was measured by the median infectious dose of the tissue culture (TCID 50) (MNV-1) or quantitative PCR (qPCR) (EDIM). Robust intestinal replication of MNV-1 and EDIM was observed in intestines of pups with both viruses peaking between 3 and 5 days postinoculation (dpi) and clearing between 7 and 10 dpi. Similar findings were also obtained in adult mice.
Implications
Annually, noroviruses, rotaviruses, and astroviruses combined infect approximately millions of people in developed and developing countries, causing significant morbidity and mortality. The various sanitation practices do not allow the fecal-oral route as the only route of transmission.
We have shown that the salivary glands (SG) are significant replication sites for these viruses on par with the intestines; Saliva transmits the infection to other people, including nursing mothers.
Additionally, SGs can act as reservoirs , whereby they continue to spread enteric viruses through saliva in the absence of diarrhea. Our results focus on enteric viral infection of SGs and saliva as a potentially more significant transmission route through talking, coughing, sneezing, and kissing compared to the accepted mode of transmission, fecal contamination.
Comments (NIH)
A class of viruses known to cause severe diarrheal illness , including the one famous for widespread outbreaks on cruise ships, can grow in the salivary glands of mice and spread through their saliva, scientists at the National Institutes of Medicine have found. Health. The findings show that there is a new transmission route for these common viruses, which affect billions of people each year around the world 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 have the potential to spread viruses. The new findings still need 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, which could save lives. The study was led by the National Heart, Lung, and Blood Institute (NHLBI), part of the NIH.
Researchers have known for some time that enteric viruses, such as noroviruses and rotaviruses , can be spread by eating food or drinking liquids contaminated with fecal matter containing these viruses. Enteric viruses were thought to bypass the salivary gland and travel to the intestines, later exiting through feces. Although some scientists have suspected that there may be another route of transmission, this theory remained largely unproven until now.
Now researchers must confirm that salivary transmission of enteric viruses is possible in humans . If they find that it is, the researchers said, they may also find that this route of transmission is even more common than the conventional route. A finding like that could help explain, they said, why the large number of enteric virus infections each year around the world fails to adequately explain fecal contamination as the only route of transmission.
"This is completely new territory because these viruses were thought to only grow in the intestines," said lead author Nihal Altan-Bonnet, Ph.D., head of the Host-Pathogen Dynamics Laboratory at the NHLBI. “Salivary transmission of enteric viruses is another layer of transmission that we did not know about. “It’s a whole new way of thinking about how these viruses can be transmitted, how they can be diagnosed, and most importantly, how their spread can be mitigated.”
Altan-Bonnet, who has studied enteric viruses for years, said the discovery was completely fortuitous . His team had been conducting experiments with enteric viruses in baby mice, which are the animal models of choice for studying these infections because their immature digestive and immune systems make them susceptible to infections.
For the current study, the researchers fed a group of newborn mice that were less than 10 days old with norovirus or rotavirus. The mouse pups were then returned to the cages and allowed to nurse from their mothers, who were initially virus-free. After just one day, one of Altan-Bonnet’s team members, NHLBI researcher and study co-author, Sourish Ghosh, Ph.D., noticed something unusual. The mouse pups showed an increase in IgA antibodies , important disease-fighting components, in their intestines. This was surprising considering that the mouse pups’ immune systems were immature and were not expected to produce their own antibodies at this stage.
Ghosh also noticed other unusual things: The viruses were replicating in the mothers’ breast tissue (milk duct cells) at high levels. When Ghosh collected milk from the breasts of mouse mothers, he discovered that the timing and levels of the IgA increase in their breast milk mirrored the timing and levels of the IgA increase in their pups’ intestines. It appeared that infection in the mothers’ breasts had increased 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 entered 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 home for their mothers to eat. That’s when researchers decided to see if the viruses in the mothers’ mammary tissue could come from the saliva of infected puppies and somehow spread during nursing.
To test the theory, Ghosh collected samples of saliva and salivary glands from mouse pups and found that the salivary glands were replicating these viruses at very high levels and shedding the viruses into the saliva in large quantities . Additional experiments quickly confirmed the salivary theory: breastfeeding had caused viral transmission from both mother to calf and calf to mother.
The research reported in this study was funded by the NHLBI Division of Intramural Research, part of the NIH. Additionally, the research involved collaboration with two laboratories at the NIH’s National Institute of Dental and Craniofacial Research: the Biology and Utilization of Adeno-Associated Viruses for Gene Transfer Laboratory (ZIA-DE000695) and Stem/Progenitor/Stem Cell Function. neurons during the development of salivary glands laboratory (ZIA-DE00722).
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