Beset in mucus, coronavirus particles likely travel farther than once
thought, study finds
Mucus shell keeps viral payload moist, enhancing journey of respiratory droplets

Date:
February 15, 2022
Source:
DOE/Pacific Northwest National Laboratory
Summary:
A modeling study raises questions about how far droplets, like
those that carry the virus that causes COVID-19, can travel before
becoming harmless.



FULL STORY ==========================================================================
A modeling study raises questions about how far respiratory droplets,
like those that transmit the virus that causes COVID-19, can travel
before becoming harmless. Can the airborne particles that carry the virus remain infectious not just for a few feet but rather more than 200 feet, farther than the length of a hockey rink?

========================================================================== Experiments dating to the 1930s proposed two paths for respiratory
droplets like those from a sneeze or cough. Either they are big and
heavy, plummeting to the ground without much chance of infecting another person. Or they are so small and light that they dry out almost instantly, remaining airborne but becoming harmless very quickly. The dryness renders "enveloped" viruses like coronaviruses unable to infect.

But a new study from scientists at the Department of Energy's Pacific
Northwest National Laboratory suggests a third option -- that small
respiratory particles can remain moist and airborne for a longer time
and greater distance than scientists have recognized.

"There are reports of people becoming infected with a coronavirus downwind
of an infected person or in a room several minutes after an infected
person has exited that room," said Leonard Pease, the corresponding
author of the study.

The findings were published in the February issue of the journal
International Communications in Heat and Mass Transfer.

"The idea that enveloped virions may remain well hydrated and thus
fully infective at substantial distances is consistent with real-world observations.

Perhaps infectious respiratory droplets persist longer than we have
realized," Pease added.

The PNNL team took a long look at the mucus that coats the respiratory
droplets that people spew from their lungs. Scientists know that mucus
allows many viruses to travel further than they otherwise would, enabling
them to journey from one person to another.



========================================================================== Conventional wisdom has been that very small, aerosolized droplets of
just a few microns, like those produced in the lungs, dry out in air
almost instantly, becoming harmless. But the PNNL team found that mucus
changes the equation.

The team found that the mucus shell that surrounds respiratory droplets
likely reduces the evaporation rate, increasing the time that viral
particles within the droplets are kept moist. Since enveloped viruses
like SARS-CoV-2 have a fatty coating that must be kept moist for the
virus to be infectious, the slower evaporation allows viral particles
to be infectious longer.

The team estimates that droplets encased in mucus could remain moist
for up to 30 minutes and travel up to about 200 feet.

"While there have been many factors proposed as variables in how COVID spreads," said Pease, "mucus remains largely overlooked." Authors of
the paper include Pease and Nora Wang Esram, Gourihar Kulkarni, Julia
Flaherty and Carolyn Burns.



========================================================================== Viral journeys between offices The focus on mucus helps address another question: how the virus moves in a multiroom office building.

Hitching a ride within respiratory droplets is the first step for the
virus to become airborne and infect those who breathe it in. Chemist
Carolyn Burns had the task of creating artificial, respiratory-like
droplets to study how the particles moved from room to room.

Ultimately, Burns settled on two substances to carry artificial virus-like particles. One was bovine mucus; the other was sodium alginate, a compound derived from brown seaweed. The compound is commonly used as a thickening
agent in foods like ice cream and cheese.

The team used an airbrush to disperse droplets in one room of a multiroom laboratory building. Together, the droplets and airbrush simulated a
person's coughing fit, releasing particles for about one minute in a
source room. A team led by Alex Vlachokostas and Burns measured droplet
levels in two adjoining rooms with controlled building ventilation.

The team's experimental findings, published Jan. 19 in Indoor Air, echo
the findings of its previous modeling study, published last year in the
journal Building and Environment.

The scientists found that both low and high levels of filtering
were effective at reducing levels of respiratory droplets in all
rooms. Filtration quickly cut down the levels of droplets in the
adjoining rooms -- within about three hours, to one-third the level or
less without filtration.

The team also found that increasing ventilation rapidly reduced particle
levels in the source room. But particle levels in the other connected
rooms jumped immediately; levels spiked 20 to 45 minutes later with
vigorous air changes increasing the spike. Ultimately, after the initial
spike, levels of droplets in all the rooms gradually dropped after three
hours with filtration and after five hours without it.

The scientists say that increased air exchange for crowded spaces may
be beneficial in certain situations, like large conferences or school assemblies, but in normal work and school conditions, it may actually
increase transmission rates throughout all rooms of a building.

"If you're in a downstream room and you're not the source of the virus,
you probably are not better off with more ventilation," said Pease.

Authors of the Indoor Air paper include Burns, Vlachokostas and Pease
as well as Timothy Salsbury, Richard C. Daniel, Daniel P. James, Julia
E. Flaherty, Nora Wang Esram, Ronald M. Underhill and Gourihar Kulkarni.

Both projects were funded through the National Virtual Biotechnology Laboratory, a consortium of all 17 DOE national laboratories focused
on response to COVID-19, with funding provided by the Coronavirus Aid,
Relief, and Economic Security (CARES) Act. The projects are among several studies at PNNL to learn more about the SARS-CoV-2 virus and COVID-19.

========================================================================== Story Source: Materials provided by
DOE/Pacific_Northwest_National_Laboratory. Original written by Tom
Rickey. Note: Content may be edited for style and length.


========================================================================== Journal References:
1. Leonard F. Pease, Na Wang, Gourihar R. Kulkarni, Julia E. Flaherty,
Carolyn A. Burns. A missing layer in COVID-19 studies: Transmission
of enveloped viruses in mucus-rich droplets. International
Communications in Heat and Mass Transfer, 2022; 131: 105746 DOI:
10.1016/ j.icheatmasstransfer.2021.105746
2. Alex Vlachokostas, Carolyn A. Burns, Timothy I. Salsbury, Richard C.

Daniel, Daniel P. James, Julia E. Flaherty, Na Wang, Ronald
M. Underhill, Gourihar Kulkarni, Leonard F. Pease. Experimental
evaluation of respiratory droplet spread to rooms connected
by a central ventilation system. Indoor Air, 2022; 32 (1) DOI:
10.1111/ina.12940
3. Leonard F. Pease, Na Wang, Timothy I. Salsbury, Ronald M. Underhill,
Julia E. Flaherty, Alex Vlachokostas, Gourihar Kulkarni, Daniel
P. James.

Investigation of potential aerosol transmission and infectivity
of SARS- CoV-2 through central ventilation systems. Building and
Environment, 2021; 197: 107633 DOI: 10.1016/j.buildenv.2021.107633 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/02/220215113354.htm

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