SALT LAKE CITY, UT. — In early 2020, news of a deadly virus caused panic buying of toilet paper and cleaning supplies. Fast forward two years later and scientists know that SARS-CoV-2 (the virus that causes COVID-19 infection) is primarily spread through respiratory droplets in the air rather than on surfaces. New research suggests mucus makes coronaviruses stuck on surfaces less infectious.
Previous research showed that coronaviruses can stay on surfaces for days or weeks, but the strongest evidence of transmission comes from airborne droplets carrying the virus. The issue lies in the method behind the studies. Most scientists looked at viruses in buffers or growth media. But in actuality, an infected person who sneezes on a desk will let out mucus-covered SARS-CoV-2.
Mucus has sugar molecules that block the COVID virus from infecting cells
The study authors looked to see how mucus may stop prolonged viral exposure on surfaces. Beyond water, salts, lipids, DNA, and other proteins, mucus has proteins called mucins that have sugar molecules known as glycans. Glycans are important because SARS-CoV-2 spike proteins target these sugar molecules at the end of the cell surface to infect cells. Therefore, if spike proteins become coated with glycans in mucus, they may not bind to the ones on cell surfaces.
Using a mock version of a human coronavirus called OC43, the team put droplets of the virus in a buffer or growth medium with 0.1-0.5% mucins found in nasal mucus and saliva found on a plastic surface. They measured the residue and its ability to infect cells.
Mucus-covered viruses were dramatically less infectious. They also found similar results when the mucins came from steel, glass, and surgical mask surfaces. The team observed that the infectiousness may have come from mucin moving from the edge, creating a coffee-ring effect when the droplets dried. The movement brought mucins and viruses together to make it easier to interact together.
The study is available to read in ACS Central Science.