NIH Scientists’ Study Reveals Saliva as a Potential Transmission Route for Norovirus and Other “Stomach Viruses”

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Scientists from the National Institutes of Health have discovered that certain viruses can grow inside mice’s glands. One of these viruses is known to cause severe diarrheal diseases and spread through their saliva. Scientists from the National Institutes of Health discovered a new method of transmitting these viruses, which affect billions of people around the world each year.

This so-called “enteric virus” can be spread through saliva. Kissing, talking, sneezing, sharing food, or utensils, as well as sneezing, could all spread the virus. These findings must be tested on human beings.

The findings published in Nature may help diagnose and treat diseases, potentially saving lives. The National Heart, Lung, and Blood Institute, a part of NIH, conducted the study.

A mouse salivary gland epithelial cell infected with rotavirus. Nihal Altan-Bonnet (NIH/NHLBI)

Researchers have known for a long period of time that enteric viruses, such as noroviruses and rotaviruses, can be transmitted by eating or drinking food or liquids contaminated with fecal matter containing these virus. It was believed that the enteric virus bypassed salivary glands, and instead targeted the intestines. This theory is largely untested despite the suspicions of some scientists.

Researchers must now confirm if salivary transmission can occur among humans. If they confirm this, researchers said they may also discover that this route of transmission is even more common. This discovery could explain why fecal infection is not the only way to transmit the many enteric viruses infected every year.

It is a new field because previously it was believed that the viruses could only be found in the intestines. Nihal Altan-Bonnet, Ph.D. the head of the Laboratory of Host-Pathogen Dynamics of NHLBI said: “This territory is completely new.” “Salivary viral transmission is a layer of transmission we weren’t aware of.” This is an entirely new way of thinking about how viruses can spread, be detected, but most importantly, how they can be minimized.

Altan-Bonnet, who has studied enteric viruses for years, said that the discovery of this virus was completely accidental. Her team was performing experiments on infant mice when they discovered enteric viruses. The immaturity of their immune and digestive systems makes them ideal for studying these infections.

Researchers in the present study fed either noroviruses, or rotaviruses to a group of newborn mice younger than 10 day. The mice pups returned to their cages and allowed to nurse their virus-free mothers. Sourish Ghosh, Ph.D., was a researcher at the NHLBI and a co-author on this study. She was part of Altan-Bonnet’s team. After only one day, she noticed something odd. The mouse pups’ guts contained a high amount of IgA antigens. These components are essential in fighting disease. It was surprising to learn that immature immune system of mice pups were unable to produce antibodies.

Ghosh observed that the virus reproduction was high in the milk ducts of the mothers. Ghosh discovered that the IgA levels and timing in the milk collected from the mothers of the mice matched those in the pups’ guts. Researchers found that infection in the breasts of the mothers boosted the production of IgA antibody to fight viruses. This cleared infection from the puppies.

Researchers were interested in finding out how the virus entered the breast tissue. The researchers conducted further experiments to confirm the mice pups didn’t transmit the virus by leaving contaminated feces in the shared living space for their mothers to consume. Researchers then investigated whether viruses in mothers’ breast tissue could have been spread by saliva from puppies.

Ghosh tested his theory by collecting salivary glands from mice pups. He discovered that the glands produced viruses at high levels and released them in large quantities to the saliva. Further experiments confirmed that salivary transmission is the cause of viral transmission between mother and pup.

This article was funded by the Division of Intramural Research of NIH’s NHLBI. This research involved collaboration with two laboratories at the NIH National Institute of Dental and Craniofacial Research: the Adenoassociated Virus biology and utilization for gene transfer lab (ZIA DE000695) and the Neuronal and Progenitor/Stem Cell Function during Salivary Gland Development lab (ZIA DE00722).

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