The transmission of coronavirus is affected by the shape of the virus

Since the start of the COVID-19 pandemic, images of the coronavirus, SARS-CoV-2, have been burned into our minds. But the way we think of the virus, usually as a spiked sphere, is not strictly accurate. Microscopic images of infected tissues revealed that coronavirus particles are actually elliptical, showing a wide variety of crumpled and elongated shapes.

Now, a global research team including scientists from Queen’s University, Canada, and the Okinawa Institute of Science and Technology (OIST), Japan, has modeled how different elliptical shapes affect the way these virus particles spin in liquids, influencing the how easily a virus can be transmitted. The study was recently published in Physics of liquids.

“When coronavirus particles are inhaled, these particles move into the nasal passages and lungs,” said Professor Elliot Fried, who heads the Department of Mechanics and Materials at OIST. “We’re interested in exploring the extent to which they are mobile in these environments.”

The specific type of motion the scientists are modeling is known as rotational diffusivity, which determines the rate at which particles rotate as they move through a liquid (in the case of the coronavirus, droplets of saliva). The particles, which are smoother and more hydrodynamic, encounter less drag from the fluid and spin faster. For coronavirus particles, this rotation speed affects how well the virus can attach to and infect cells.

“If the particles spin too much, they may not spend enough time interacting with the cell to infect it, and if they spin too little, they may not be able to interact in the way they need to,” explained Prof. Freed.

In the study, the scientists modeled both elongated and flattened ellipsoids of revolution. These shapes differ from spheres (which have three axes of equal length) in only one of their axes, with elongated shapes having one longer axis, while oblate shapes having one shorter axis. Taken to an extreme, elongated shapes are elongated into rod-like shapes, while flattened shapes are crushed into coin-like shapes. But for coronavirus particles, the differences are more subtle.

The scientists also made the model the most realistic yet by adding protein spikes to the surface of the ellipsoids. Previous research from Queen’s University and OIST has shown that the presence of triangular-shaped spike proteins reduces the speed at which coronavirus particles spin, potentially increasing their ability to infect cells.

Here, the scientists modeled the spike proteins in a simpler way – with each spike protein represented by a single sphere on the surface of the ellipsoids.

“We then figured out the arrangement of the spikes on the surface of each ellipsoidal shape, assuming they all contained the same charge,” explained Dr Vikash Chaurasia, a postdoctoral researcher in OIST’s Department of Mechanics and Materials. “Spikes with the same charges repel each other and prefer to be as far apart as possible. They therefore end up being uniformly distributed throughout the particle in a way that minimizes this repulsion.

In their model, the researchers found that the more a particle deviates from a spherical shape, the slower it rotates. This may mean that the particles are better able to arrange themselves and attach to cells.

The model is still simplistic, the researchers admit, but it brings us one step closer to understanding the transport properties of the coronavirus and may help determine one of the factors key to its infectious success.

Reference: Kanso MA, Naime M, Chaurasia V, Tontiwattanakul K, Fried E, Giacomin AJ. Coronavirus pleomorphism. Physical fluids. 2022;34(6):063101. doi: 10.1063/5.0094771

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