by Bruce Leander
This guest post comes from Bruce Leander, who shares his view of the coronavirus in comparison to the grains of pollen viewed through his camera lens. For the last decade Bruce has been the volunteer photographer for the Lady Bird Johnson Wildflower Center and an occasional speaker at Travis County Master Gardener meetings. He is the husband of Master Gardener Patty Leander.
This COVID-19 pandemic got me thinking about how small the virus particle is relative to plant pollen grains, and how our bodies try to protect us from pathogen and allergen invaders. I did some research and thought I would share it here for others who may also be interested. My last job involved working with an Austin company named Ambion, The RNA Company. We focused on research products relating to the molecule RNA (ribonucleic acid). I even have a t-shirt that says, “RNA – the other nucleic acid.” Why does this matter? The Coronavirus is an RNA virus consisting of positive-sense, single-stranded RNA enclosed in a protein coat. It’s called coronavirus because the spherical external spike protein displays a characteristic crown shape when observed under an electron microscope. This new virus is known as SARS-CoV-2. It is a SARS virus (severe acute respiratory syndrome) very similar to the SARS virus that appeared in China in 2003, spread around the world and killed about 800 people (SARS-CoV). So, this is the second known SARS coronavirus, and the name has been shortened to COVID-19 (COronaVIrus Disease, designating the year it was identified, 2019).
Considering size first, the virus particle is extremely small, approximately 0.125 microns. When I take pictures of wildflowers, I think metric, usually centimeters (cm) and millimeters (mm). 2.54 cm equals one inch, so that gives you a rough idea how long a centimeter is. There are 10 mm in a cm. If this writing were printed out on an 8.5×11” piece of paper at a font size of 11, a mm would be about as wide as the inside of the letter “o”. There are 1000 microns in a mm so 1000 microns fit across the width of the letter “o”. The coronavirus particle size is about a tenth of one of those thousand microns!!!
Here is another way to get a sense for the size of a COVID-19 virus particle.
One virus particle is 0.125 microns. It would take about 8,000 virus particles lined up side-by-side to span 1 mm. That is why you can only see them under an electron microscope, which can magnify images up to 200,000x. With my equipment I can magnify a maximum of 10x.
Luckily, they don’t just blow around in the air – they are contained within droplets of water. Most droplets caused by coughing are 5-10 microns and they don’t travel very far because they are relatively heavy – less than 3 feet. The CDC set 6 feet as a safe social distance because they felt it was a sensible safe distance from people with the virus who are coughing or sneezing. A paper I recently read said the primary mode of COVID virus transmission was through coughing or sneezing and much less through hand contact with droplets that contain the virus. However, coronavirus can also be contained within water droplets less than 5 microns which are known as droplet nuclei or aerosols. These can remain in the air longer and travel further depending on humidity and air movement. They also have the potential to travel further into the body toward the alveoli in the lungs.
I think about how small things are all the time as I take pictures at the Wildflower Center. Here is a picture I took of a common sunflower and its pollen. Each pollen grain is about 30 microns across. It is relatively large so it is mostly transferred to other sunflower plants via insects.
Rock rose pollen (below) is 140-180 microns. Huge! The human eye can resolve down to about 0.1mm so we can see the rock rose pollen grains (0.18mm). COVID-19 is so minute, 1,300 virus particles would fit across one rock rose pollen grain.
Ragweed (below) is wind pollinated, so the pollen grains are very small: 16-27 microns. The average size of any airborne pollen is 25 microns. It is not a very efficient way to pollinate other plants because so much pollen must be produced and carried in the air to find where it is supposed to end up (on the stigma of a plant of the same species). A single plant can produce billions of pollen grains in one season. That means some find its way to another ragweed plant and pollinates it but all the extra ends up on our cars as fine yellow dust or into our noses and eyes causing allergy symptoms. These pollen grains can travel hundreds of miles.
Airborne pollen such as ragweed, finds its way into our bodies primarily through our eyes, nose and mouth. For people that are allergic, the body senses something foreign and reacts with an immunological response to kill it. The thing is, it is a plant, not an animal virus, so although a foreign body, it is not really dangerous in the sense that it’s going to try to kill you. The COVID-19 virus is also a foreign molecule entering our bodies, but it is much more insidious. It is animal based. It is very easily transmitted and very contagious. Like allergens, it enters moist areas of our bodies like eyes, nose and throat but then attaches to our cells through protein/protein interactions and then enters those cells and uses its RNA message to instruct our cells and cell machinery to make more virus particles, and kills our cells in the process. It is a respiratory virus (SARS) and starts off as an upper respiratory infection replicating in the throat. If our immune response controls and rejects the insult, then we recover. The bigger problem is if the virus moves into the lower respiratory tract (the lungs) where the situation can get much worse. The virus moving into the lungs can cause viral pneumonia or a condition known as acute respiratory distress syndrome. This is serious and can require hospitalization, supplemental oxygen or being put on a ventilator. A ventilator doesn’t cure you, it just buys you some time for your body to fight the virus.
Part of the challenge with COVID-19 is that it is a new, unique virus that our bodies have never before been exposed, and our bodies are not conditioned to fight it off effectively. In addition, our medical system is not prepared for a pandemic of this size, uniqueness, and severity. In this age when medicine has come SO far in the last century, it is amazing that the best short-term medical solution to this pandemic is for people to stay 6 feet apart from each other. This is a very low tech, and a rather crude strategy.
If there is a silver lining in all this, it is the opportunity to learn more about RNA viruses, how to prevent them, and how to treat and cure them. This translates to benefits for future virus threats, the common cold and the yearly flu. It takes time, money and research. It is a question of whether we and our government have the will to do that once this immediate threat subsides.
This will likely be the biggest event of our lifetime …and it will have been caused by something that is only 0.125 microns in size. And now you know how small that really is.
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