The COVID-19 virus spreads via mucus once inside an infected airway, allowing it to reach into the lower lungs, according to a Northwestern Medicine study published in Nature Communications.

More than 770 million cases of COVID-19 have been reported to the World Health Organization since the onset of the pandemic in 2020.

While it's understood that the virus latches onto healthy cells in the nose and throat to copy itself, not much is known about the process by which it spreads once inside an infected airway.

To better understand how the virus proliferates, investigators in the laboratory of Thomas Hope, Ph.D., professor of Cell and Developmental Biology and of Obstetrics and Gynecology and senior author of the study, performed live imaging of human bronchial epithelium cells exposed to COVID-19.

In the study, investigators observed that the movement of mucus can spread the COVID-19 virus inside the respiratory tract, where it later forms aerosols that infect other people. Additionally, the virus travels on mucus to infect deeper into the lower lung.

"The virus goes where the mucus goes," said Mark Becker, a student in the Driskill Graduate Program in Life Sciences (DGP) and first author of the study.

Although mucus is generally thought to protect against infection by trapping and removing viruses and other particles, COVID-19 appears to exploit mucosal spread following an infection, Becker said.

As funding begins to dwindle for COVID-19 research, Hope said the discovery could prove useful in other viral diseases, such as HIV.

"Interestingly, the mucosal environment most similar to the lungs is the upper female reproductive tract," Hope said.

"The infrastructure at Feinberg really helped us build the facilities needed for this research," Hope said. "The university really supported us and that is a testament to what a great environment Feinberg is."