Lung cell images show how intense a coronavirus infection can be

Microscopic views reveal virus particles coating the hairlike cilia of an airway cell

false-color microscope image of small virus particles on a lung cell

Coronavirus particles (red) overwhelm a human lung cell (blue and purple) in this artificially colored scanning electron micrograph. Mucus is highlighted in green.

Ehre Lab/UNC School of Medicine

New closeup views of lung cells show just how prolifically the coronavirus that causes COVID-19 can replicate once it infiltrates the respiratory tract. 

In the lab, pediatric pulmonologist Camille Ehre and colleagues at the University of North Carolina at Chapel Hill infected cells that line the airways in the lungs with SARS-CoV-2, waited 96 hours and then snapped scanning electron micrograph images of the virus-laden cells.

“Once a cell is infected, it is completely taken over by the virus, producing an astonishing number of viruses,” Ehre says. In a lab dish of about 1 million human cells, she says the viral load can skyrocket from about one thousand infectious viruses to 10 million in just two days. The new images were published September 3 in the New England Journal of Medicine.

Cells that line the respiratory tract and their hairlike protrusions called cilia help clear airways of inhaled particles and pathogens. These types of cells are also specifically targeted by the coronavirus. Once infected, they churn out “astronomical numbers” of viral particles, Ehre says, potentially propelling the particles deeper into the lungs, which can cause pneumonia, or out into the air where they can infect others.

“These images of airway cells jam-packed with viruses make a strong case for the use of masks to limit SARS-CoV-2 transmission whether an individual has symptoms or not,” Ehre says. Widespread mask wearing could help contain such explosive viral replication from spreading beyond a single individual.

black and white microscope images of round coronavirus particles coating the hairlike cilia of a lung cell
Coronavirus particles (small, spiky spheres) coat a human lung cell and its hairlike cilia in this scanning electron micrograph (left; higher-resolution view at right).C. Ehre/NEJM 2020

Jonathan Lambert is a former staff writer for biological sciences, covering everything from the origin of species to microbial ecology. He has a master’s degree in evolutionary biology from Cornell University.

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