You’ve probably heard the term viral shedding at some point during the covid-19 pandemic. Here’s what it actually looks like and what it means.
This incredible image was captured by Elizabeth Fischer, head of Rocky Mountain Laboratories, a National Institutes of Health research lab in Hamilton, Montana. Fischer has imaged all sorts of viruses over the past 25 years, but this image taken with a scanning electron microscope (SEM), shows a virus we’re all too familiar with: SARS-CoV-2, the pathogen responsible for covid-19.
Writing in his director’s blog at the National Institutes of Health, physician-geneticist Francis Collins explains the image:
The orange-brown folds and protrusions are part of the surface of a single cell that’s been infected with SARS-CoV-2. This particular cell comes from a commonly studied primate kidney epithelial cell line. The small, blue spheres emerging from the cell surface are SARS-CoV-2 particles.
This picture is quite literally a snapshot of viral shedding, a process in which viral particles are released from a dying cell. This image gives us a window into how devastatingly effective SARS-CoV-2 appears to be at co-opting a host’s cellular machinery: just one infected cell is capable of releasing thousands of new virus particles that can, in turn, be transmitted to others.
Capturing an image like this is not a straightforward process. Fischer had to carefully time the shot to capture the virus particles emerging from the infected cell. And yes, this is exactly what viruses do: They hijack cells, converting them into factories that produce more virus. Nasty stuff.
And indeed, SARS-CoV-2 seems to be proficient at replicating itself and spreading not just to new cells but also to new hosts.
Covid-19 has an estimated basic reproduction number (R0) between 2.2 and 3.9. Pronounced “R-nought,” this value describes the average number of people that an infected person will go on to infect, and it gives epidemiologists a rough idea of a virus’s ability to spread through a population. That said, R0 describes an idealised scenario, in which immunity, physical distancing measures, and other factors, such as vaccines, are not present.
By comparison, influenza has an R0 rating between 0.9 to 2.1, while measles has an astounding R0 between 12 and 18. Yikes.
The new microscopic image and others like it are important because they could tell us new things about the novel coronavirus, like how it infiltrates and moves inside of cells and emerges to infect other cells nearby. Pictures like this are also important because they turn an invisible threat into something tangible, providing us with a snapshot of our common enemy.
We literally see you, SARS-CoV-2—and we’re coming for you.