A Viral Primer

by J. Bruce Neill, Ph.D.

In the very broadest of terms, there are three major categories of living things on our planet: true bacteria, ancient bacteria, and everything else. Two things are noteworthy in the previous sentence. First, viruses are not included (they are not in everything else). Secondly, I use the term “everything else” as one large category — technically they are the eukaryotes, which include plants, animals, fungi, and all single-celled organisms that are not bacteria.

In biology, the study of living things, we utilize a set of characters to define “living.” Primarily, they have the ability to utilize energy to become organized, they reproduce, and they are composed of individual units called “cells” (organisms may be composed of many cells, or they may be a single cell). Although viruses are composed of a structure that is similar to a cell, they do not have the ability to reproduce without the utilization of another organism (called a “host cell”), nor do they consume energy.

Viruses were first discovered in 1892 in the tobacco plant. And yes, viruses attack plants, animals, and even bacteria. An individual virus is known as a viral particle, or a virion. It is composed of a protein-like outer shell, surrounding either DNA or RNA. Viruses invade a cell and direct the cell’s machinery to make new copies of the virus.

What is a Coronavirus?

The virus responsible for COVID-19 is a Coronavirus. There about 40 different types of known coronaviruses. Seven have been reported to infect and cause disease in humans. Four or these cause mild symptoms similar to the common cold, but three coronaviruses cause severe and potentially deadly infections.

The three strains known to cause infections in humans are: SARS-CoV, the Severe Acute Respiratory Syndrome coronavirus, MERS-CoV, the Middle East Respiratory Syndrome coronavirus, and now, SARS-CoV2, which is responsible for the current coronavirus disease COVID-19.

Of course, this is still uncertain, but for now, it appears that SARS-CoV2 is less deadly than the other two coronavirus strains, but more contagious. The mortality rate for SARS was around 10 percent. The mortality rate for MERS was around 37 percent. Although uncertain, our best understanding of the mortality rate for COVID-19 is around 1 percent.

How are viruses transmitted?

Different types of viruses spread in different ways. One transmission pathway is through disease-bearing organisms known as vectors. Viruses are often transmitted from plant to plant by insects that feed on plant sap, such as aphids; viruses in animals can be carried by blood-sucking insects. Influenza viruses are spread by coughing and sneezing. Norovirus and rotavirus, common causes of viral gastroenteritis, are transmitted by the fecal-oral route, entering the body in food or water. HIV is one of several viruses transmitted through sexual contact and by exposure to infected blood.

Why do we call it a ‘novel’ virus?

Most new viral diseases in humans are zoonotic, meaning that they originate in wild animals (mostly mammals) and then cross over to people. Among mammals, bats have a higher number of zoonotic viruses.

In the 2003 SARS outbreak, the coronavirus jumped from bats to civets – a small type of primate that were being sold as food in a market, and then from civets to people. In the 2012 MERS outbreak, the MERS coronavirus jumped from bats to camels and then from camels to people. We do not yet know the path for SARS-CoV2 coming into humans, but it seems likely that it was originally in bats. As a result of the COVID-19 epidemic, China placed a permanent ban on wild animal markets.

While you are sheltering, washing your hands frequently, and keeping a safe distance from others, take time to go outside and enjoy nature. Breathe fresh air, get some exercise and let the wonders of our natural world ease your tension and anxieties. This will pass, and we will have a better future for what we have learned.