Microbiology: Transmission of gastrointestinal viruses in saliva

Gastrointestinal viruses such as norovirus and rotavirus may be transmitted through saliva, suggests a study of mice published in Nature. The findings uncover a previously unknown route of transmission for this group of viruses, which may mean that measures to contain viral spread need improved sanitation techniques.

Gastrointestinal (also called enteric) viruses cause stomach pains, vomiting and diarrhea, and are widely accepted to spread via the faecal–oral route: viruses in the faeces of one host enter another (through contaminated food, for example), replicate in the gut and then shed in the faeces, and the replication cycle continues. Although genomic RNA from enteric viruses has been detected in the saliva of infected individuals, such observations have been attributed to gut contaminants. However, Nihal Altan-Bonnet and colleagues present evidence that enteric viruses infect the salivary glands of mice and that saliva can transmit infection to others.

The authors observed that a few days after mouse pups were inoculated with murine norovirus or rotavirus, their mothers also showed signs of infection. Genomic RNA from murine norovirus or rotavirus was found in the mothers’ mammary glands, indicating that this may be the site of enteric virus replication and therefore suggesting that the pups suckling milk may have been the route of transmission. In adult mice, some (but not all) strains of murine norovirus or rotavirus were shown to replicate in salivary glands, and inoculating pups with saliva from infected adults led to infection.

The discovery that enteric viruses replicate in the salivary glands may have implications for the study of viruses and potential treatments. Mini saliva glands — organoids derived from mouse or human salivary gland cells — could be used to cultivate mouse and human noroviruses, respectively, the authors demonstrate. These systems might be a cheaper and simpler alternative to ‘mini gut’ organoid systems currently used to replicate norovirus for research purposes.