Updated on 06/30/2022 at 08:07
- Gut bacteria such as norovirus or rotavirus cause gastrointestinal infections and can cause diarrhea and vomiting.
- Until now, scientists assumed that pathogens are transmitted mainly via faecal residues.
- However, they have now found out that infection is also possible through saliva.
Noroviruses and rotaviruses, which cause gastrointestinal infections, can also be transmitted through saliva. This has been shown in a study in mice and human salivary gland cells.
Until now, doctors had generally assumed that infection with these viruses was almost exclusively via the faecal-oral route: small amounts of faeces, for example from contaminated food or drinking water, enter the mouth. The group led by Nihal Altan-Bonnet of the National Institutes of Health in Bethesda (Maryland, USA) describes the newly discovered pathway of infection in the journal Nature.
Until now, virus particles in saliva have not been considered contagious
‘Our results highlight salivary gland infection with intestinal viruses and saliva as a potentially more significant route of transmission through coughing, sneezing and kissing compared to the accepted route of transmission, faecal contamination,’ the researchers write. The results indicate that hygiene measures, in addition to those that prevent the spread of feces, may be needed to prevent the transmission of intestinal viruses to the community.
Noro- and rotaviruses multiply in the intestinal wall and cause abdominal pain, nausea, vomiting and diarrhea in those infected. According to the 2018 Global Burden of Disease study, approximately 300 million children are infected with these viruses each year, and around 200,000 children die.
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In recent years, the media has repeatedly reported outbreaks of disease from these intestinal viruses in nursing homes or on cruise ships. Although virus particles were already found in the saliva of infected people, they were thought to be a byproduct of an intestinal infection and were not contagious.
Infection during breastfeeding possible in both directions
A study by Altan-Bonnet and colleagues now shows that viruses infect the salivary glands and can be transmitted through saliva.
Scientists infected healthy infant mice with norovirus and rotavirus and were able to show that they transferred the virus to the mother while suckling. The mother infected in this way passed the virus along with the mother’s milk to other healthy offspring of mice. When breastfeeding, infection is possible in both directions: from baby to mother and from mother to baby. This suggested that the infection spread from infant to mother through the baby’s saliva.
This was evidenced by an experiment in which the saliva of infected mice was administered to healthy children of mice that became ill. Scientists also investigated whether the viruses can multiply in the cells of the salivary glands. After infecting mice with the different strains of virus, the amount of virus in the salivary glands was 10,000 times higher after five days compared to six hours after infection. In the case of the norovirus strains MNV-3, MNV-4 and WU23, the extent and duration of viral replication was comparable to that of the central gut. On the other hand, CR6 norovirus was unable to reproduce in the salivary glands.
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Scientists point to the possibility of conducting medical research
Finally, scientists cultivated human salivary gland cells in the laboratory and were able to show that noroviruses reproduce in large numbers in them.
Elizabeth Kennedy and Megan Baldridge of Washington University School of Medicine in St. Louis (Missouri, USA) in the comment “Nature” point to the possibility of conducting medical research: When certain strains of norovirus multiply in the salivary glands as well as in the gut, then they could be easier to study: “3D cultures of human intestinal cells, known as miniguts have been developed to grow human noroviruses, but working with them can be costly and difficult. ‘ Instead, simpler “mini salivary gland” models can now be used. (ff / dpa)
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