Since the beginning of the COVID-19 pandemic, pictures of the coronavirus known as SARS-CoV-2 have been embedded in our memories.

However, the way we commonly imagine the virus—as a spherical covered with spikes—is not entirely true. The coronavirus particles are actually ellipsoidal, showing a variety of squashed and elongated morphologies, as seen by microscope images of infected tissues.

A global study team led by experts from Queen’s University in Canada and the Okinawa Institute of Science and Technology (OIST) in Japan has now analyzed how different elliptical shapes alter the way viral particles rotate within fluids, influencing how easily the virus can be transferred. The research was just published in the journal Physics of Fluids.

“When coronavirus particles are inhaled,” as explained by Professor Eliot Fried, “these particles move around within the passageways in the nose and lungs.

“We are interested in studying to what extent they are mobile in these environments.”

The scientists modeled a specific form of movement known as rotational diffusivity, which controls the pace at which particles rotate as they move through a fluid (in the case of the coronavirus, droplets of saliva). Smoother, more hydrodynamic particles rotate more quickly because there is less drag resistance from the fluid. This rotational speed has an impact on how successfully coronavirus particles can bind to and infect cells.

Prof. Fried noted that if the particles rotate too much, they might not connect with the cell for long enough to infect it, and if they rotate too little, they might not be able to interact in the required way.

Scientists made models of both prolate and oblate ellipsoids of revolution for the study. These shapes only have one axe that is different from spheres, which have three axes of equal length. Prolate shapes have a long axis, whereas oblate shapes have a shorter axis. When stretched to the limit, oblate shapes condense into coin-like shapes and prolate shapes lengthen into rod-like shapes. However, the distinctions between coronavirus particles are more nuanced.

By putting spike proteins on the surface of the ellipsoids, the scientists also made the model as real as it could be. Previous studies from Queen’s University and OIST demonstrated that triangular-shaped spike proteins slow the rotation of coronavirus particles, potentially enhancing their capacity to infect cells.

Each spike protein was represented by a single sphere on the surface of the ellipsoids in this simpler model of the spike proteins developed by the researchers.

Dr. Vikash Chaurasia, a postdoctoral researcher in the OIST Mechanics and Materials Unit, noted that by assuming that they all have the same charge, they were able to determine the arrangement of the spikes on the surface of any ellipsoidal shape. 

“Spikes with identical charges repel each other and prefer to be as far from each other as possible. They, therefore, end up evenly distributed across the particle in a way that minimizes this repulsion.”

The researchers discovered in their model that the further a particle deviates from a spherical shape, the slower it rotates. This might imply that the particles can align and adhere to cells more effectively.

The researchers agree that the model is still basic, but it brings us one step closer to understanding the transport features of the coronavirus and may help identify one of the variables essential to its viral success.

Image Credit: Getty

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