High-Powered Microscopic Images Reveal Startlingly High SARS-CoV-2 Viral Loads on Human Respiratory Surfaces

Researchers from the University of North Carolina (UNC) School of Medicine (Chapel Hill, NC, USA) have produced striking images in respiratory tract cultures of the infectious form of the SARS-CoV-2 virus produced by infected respiratory epithelial cells. The researchers captured these images to illustrate how intense the SARS-CoV-2 infection of the airways can be in very graphic and easily understood images.

In a laboratory setting, the researchers inoculated the SARS-Co-V-2 virus into human bronchial epithelial cells, which were then examined 96 hours later using scanning electron microscopy. The images which were re-colorized show infected ciliated cells with strands of mucus (yellow) attached to cilia tips (blue). Cilia are the hair-like structures on the surface of airway epithelial cells that transport mucus (and trapped viruses) from the lung. A higher power magnification image shows the structure and density of SARS-CoV-2 virions (red) produced by human airway epithelia. Virions are the complete, infectious form of the virus released onto respiratory surfaces by infected host cells.


The imaging research has illustrated the incredibly high number of virions produced and released per cell inside the human respiratory system. The large viral burden is a source for spread of infection to multiple organs of an infected individual and likely mediates the high frequency of COVID-19 transmission to others. According to the researchers, the images make a strong case for the use of masks by infected and uninfected individuals to limit SARS-CoV-2 transmission.

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University of North Carolina (UNC) School of Medicine