COVID-19 Up Close

What am I looking at?

This is an electron microscopy image showing particles of the coronavirus SARS-CoV-2 covering the surface of a single cell that’s exhibiting signs of apoptosis, or programmed cell death. This sample of the virus was isolated from a human subject infected with SARS-CoV-2. You can see the virions in green (1) and the cell they’re infecting in pinkish-brown (2).

Click on the right arrow to see more views of SARS-CoV-2 virions (which are colored orange or red in the subsequent images) on the surface of cells from the respiratory system.

Biology in the background

COVID-19 is the disease that caused the global pandemic from 2020 through 2023. This disease – which is still a threat, though no longer at pandemic levels – is caused by a coronavirus known as SARS-CoV-2. The virus, which was originally referred to as “the novel coronavirus” because it wasn’t identified in humans until 2020, primarily affects the respiratory system. It spreads when an infected individual exhales, coughs, or sneezes tiny fluid particles into the air and then these particles come in contact with the mucous membranes lining the mouth, nose, or lungs of an uninfected individual.

Once a SARS-CoV-2 virion contacts a cell in the respiratory system, it uses spike proteins on its surface to bind to the membrane of the host cell. The virion then fuses its membrane with the host cell’s membrane and transfers its genetic material into the host cell’s cytoplasm. This allows the virus to hijack the replication machinery within the host cell and create more virus particles, which accumulate in the cell until it ruptures – releasing more virus into surrounding tissues and infecting nearby cells, where the replication process begins anew.

SARS-CoV-2 particles can be between 50 and 140 nanometers across, or roughly 1,500 to 500 times smaller than the width of a human hair.

Technique

These images were created using scanning electron microscopy.