Scientists at the National Institutes of Health have found that a group of viruses that are known to cause severe diarrheal disorders, including the one famous for big outbreaks on cruise ships, may thrive in mice’s salivary glands and spread through their saliva.
The results demonstrate that these widespread viruses, which can be fatal and affect billions of people annually throughout the world, have a novel pathway of transmission.
The fact that these so-called enteric viruses are shared by saliva means that other methods of transmission, such as coughing, talking, sneezing, sharing food and utensils, and even kissing, may also be effective.
Studies on humans are still required to confirm the new findings.
The research, which was published in the journal Nature, may help doctors better predict, identify, and treat illnesses brought on by these viruses, potentially saving lives.
The National Heart, Lung, and Blood Institute (NHLBI), a division of NIH, was in charge of the investigation.
It has long been understood by researchers that enteric viruses, such as noroviruses and rotaviruses, can spread through consumption of contaminated food or beverages.
It was believed that enteric viruses attack the intestines instead of the salivary gland and then leave the body through feces.
Even though some researchers hypothesized there might be another method of transmission, this hypothesis has mostly gone untested up to this point.
Now, scientists must establish if enteric viruses may spread through saliva in humans.
The researchers claimed that if they determine that it is, they may also find that this method of transmission is even more widespread than the traditional method.
A discovery like that, they suggested, would help explain why the large number of enteric virus infections each year reported globally do not sufficiently take into account fecal contamination as the exclusive route of transmission.
Since it was believed that these viruses could only flourish in the intestines, senior author Nihal Altan-Bonnet, Ph.D., director of the Laboratory of Host-Pathogen Dynamics at the NHLBI, called this “totally new ground.”
“An additional layer of transmission we were unaware of is salivary transmission of enteric viruses. It is a completely different way of thinking about how these viruses can spread, how to diagnose them, and most critically, how to perhaps stop their transmission.
Altan-Bonnet, who has long studied enteric viruses, claimed that the discovery was entirely accidental. Infant mice are the ideal animal models for researching these diseases because of their undeveloped digestive and immune systems, which leave them prone to infections.
Her team has been performing investigations with enteric viruses in these mice.
For the current investigation, the researchers administered either norovirus or rotavirus to a group of newborn mice that were less than 10 days old.
Then, the virus-free mothers of the mouse pups were put back in their cages where they could nurse them. One of Altan-team Bonnet’s colleagues, Sourish Ghosh, Ph.D., an NHLBI researcher and study co-author, noticed something peculiar after only one day.
The mouse pups’ stomachs had an increase in IgA antibodies, which are crucial elements in battling disease.
Given the immaturity of the mouse pups’ immune systems and the fact that it was not anticipated that they would be producing their own antibodies at this time, this was surprising.
Other strange occurrences were also noted by Ghosh, including the moms’ milk duct cells’ high viral replication rates.
Ghosh discovered that the time and intensity of the IgA rise in the mouse mothers’ milk coincided with those in the pups’ stomachs when he took milk samples from their breasts.
According to the researchers, it appeared that the moms’ breast infections had increased the production of virus-fighting IgA antibodies in their breast milk, which ultimately assisted in the pups’ recovery from illness.
The researchers carried out additional studies in an effort to determine how the viruses entered the mothers’ breast tissue in the first place.
They discovered that the mouse pups did not infect their moms by depositing contaminated excrement in a communal living area for the mothers to consume.
At that point, the scientists made the decision to investigate the possibility that the viruses in the mothers’ breast tissue might have originated from the saliva of the sick puppies and then spread through breastfeeding.
Ghosh gathered saliva samples and salivary glands from the mouse pups to test the notion, and he discovered that the salivary glands were highly efficient at replicating these viruses and heavily exuding them into the saliva.
Additional research immediately supported the salivary explanation, showing that nursing had triggered viral transmission from mother to pup and pup to mother.