New images capture startlingly high SARS-CoV-2 viral loads

By Angela Betsaida B. Laguipo, BSNSep 16 2020

The global health crisis, caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has now topped 29.47 million cases worldwide. The pandemic is still spreading rapidly, with many countries reporting surging cases and deaths.

Early in the pandemic, scientists revealed what the coronavirus looked like, spherical with spike proteins protruding from their surface. These spike proteins latch onto human cells and bind to the angiotensin-converting enzyme 2 (ACE2) receptors found in healthy cells, which act as the cellular gateway for the virus to enter and infect the cell to be copied, producing more viruses.

Now, a team of scientists from the University of North Carolina at Chapel Hill School of Medicine produced striking images in respiratory tract cultures of the infectious form of the SARS-CoV-2 produced by infected epithelial cells.

SARS-CoV-2 virions (red). (Ehre Lab, UNC School of Medicine)

Images of infected cells

The images, which are featured in the New England Journal of Medicine’s Images in Clinical Medicine, showed images of infected cells taken by scientists, which may provide new information on how the virus invades healthy cells. The team captured the images to illustrate how intense the infection of SARS-CoV-2 of the airways can be in clear and easily understood images.

To capture the images, the team inoculated the SARS-CoV-2 into human bronchial epithelial cells, which was done in a biosafety level 3 facility. The scientists examined the cells for 96 hours after infection, utilizing a scanning electron microscopy.

The images were re-colorized by a medical student in UNC and showed infected ciliated cells with strands of mucus, colored yellow, attached to the cilia tips, which were colored blue. Cilia are small hair-like structures on the surface of airway epithelial cells. These structures aid the transport mucus and trapped viruses from the lungs.

A higher power magnification image shows the structure and density of SARS-CoV-2 virions (red) produced by human airway epithelia. (Ehre Lab, UNC School of Medicine)

A high number of virions

Apart from the two previous colors, the team added red to show the SARS-CoV-2 virions, which was revealed using a higher power magnification image. Virions are the complete and infectious form of the virus, consisting of an outer protein shell called a capsid, and an inner core of nucleic acid, which is the RNA. The core is responsible for its infectivity, while the capsid provides specificity to the virus.

“An en face image shows an infected ciliated cell with strands of mucus attached to the cilia tips. At higher magnification, an image shows the structure and density of SARS-CoV-2 virions produced by human airway epithelial cells. Virus production was approximately 3×106 plaque-forming units per culture, a finding that is consistent with a high number of virions produced and released per cell,” the researchers wrote in the paper.

The imaging study also illustrated the markedly high number of virions produced and released per cell inside the respiratory tract, which can show how infectious SARS-CoV-2 is, the virus that causes the coronavirus disease (COVID-19).

Further, the images can show how potent the virus is and how many virions are present in a single cell, which can invade and infect other cells in the body. The study shows that the sizeable viral burden may be the culprit of the infection spread to multiple organs of an infected person. It may also explain why the virus is highly infectious, with skyrocketing numbers of cases each day. The team reiterates that the findings support the use of masks by infected and uninfected people to stem the spread of the novel coronavirus, which has now killed nearly a million people across the globe.

Several countries report surging COVID-19 cases, with the United States as the nation with the highest number of cases, surpassing 6.55 million. India follows with a staggering 4.84 million confirmed cases, while Brazil and Russia report 4.33 million and 1.06 million cases, respectively.

The U.S. reports more than 194,000 deaths tied to COVID-19, followed by Brazil and India, with more than 131,000 and 79,000 deaths, respectively.