Corona viruses, like every other virus, survives and thrives by a unique complex routine. Viruses in general are so small they cannot support a complete cell structure of their own and as a result, they cannot reproduce by themselves even by the basic biological definitions of reproduction; self replication or division. To make up for this, they instead find a host cell in which they introduce their genetic materials. Using this as a template, just like a photocopying machine, the host cells then churns out new copies of the virus. So far, about five thousand viruses have been identified and classified. And in all, either RNA or DNA viruses, regardless of shape, their basic structures are usually the same. All viruses are made of a genetic material (DNA or RNA), a molecule which carries this genetic material and a protein coating which holds all these together. Some however may even have a fat envelope around them on which there are receptors that select which particular cells the virus will be attached to.
The journey into the discovery of viruses began 1884 when French scientist Charles Chamberlain came up with the idea of a filter with pores so small, even bacteria could not filter through them. It would be later known as the Chamberlain filter. This filter came in handy in Dmitri Ivanovsky’s research in what was later identified to be the Tobacco mosaic virus, as the extracts gotten from the plant and filtered were shown to be still infective. But it wasn’t until 1931 when the electron microscope was invented by German engineers Ernest Ruska and Max Knoll that a detailed image of a virus would be seen. After that, the next challenge in the study of viruses was how to grow them outside living animals. That breakthrough came in 1931 when the influenza virus was cultured in fertilized eggs, and then polio virus in cultures of living cells in 1949.
For viruses, their cycle comprises finding a host, attaching itself to that host, penetrating the cell wall, uncoating to release its genetic material and finally replicating. All these are evolutionary adaptive mechanisms for survival. But on the other side of the table is the effect this process has in the host animal. Usually, but not always, this process leads to a disease condition in the organism, depending on the part of the organism the virus has an affinity for and the virulence of the virus itself.
Corona virus gets its name from the same Latin word “Corona” which means “crown”. This is so because of the fringes on the surface of the virus which is similar to that of a crown. They are single stranded RNA (Ribonucleic Acid) viruses with a genome size of about 26-32. It wasn’t until the invention of the electron microscope that corona viruses were able be viewed and described in their details. The most common type of corona viruses found in the nasal cavity of people suffering from the common cold and another variant which causes infectious bronchitis in chickens were the first corona viruses to be identified. These common cold virus would come to be known as “human corona virus 229E and OC43”. They belong to the order of Nidovirales and classified as a family called Coronaviridae. The spikes on the surface of the virus for which it earns its name is known as peplomers and this structure helps determine where the virus latches on to in its hosts. The virus is also made up of a membrane, an envelope and a nucleocapsid.
The oldest known common ancestor of the corona virus is about 10,000 years old according to consensus agreements, although they are believed to be much more older than this. It is also known that bats and birds are the most common hosts for this virus. However, other more recent hosts like the civet cat, camels, and bovine groups of animals have become ideal hosts for the corona virus.
When a corona virus enters a host, the spike clings to a cell in the host while the virus makes its entry into the cell cytoplasm. While inside, the next process occurs, the virus sheds its coat thereby revealing the RNA genome within. This genome is what carries the details of the virus and with which other viruses can be made. The virus essentially turns the host cells into tiny manufacturing plants, using its own genetic details as a template for replication and churning out new viruses from the cell machinery.
The process is then repeated when a new host/human is infected, usually by respiratory droplets and aerosols from an infected person. In other cases, it is from the consumption of an infected animal as in the case of SARS and Covid-19.
Not all corona viruses can be passed from animals to humans. There are currently only seven know strains that affect humans:
- Human Corona Virus 229E
- Human corona virus OC43
- Severe Acute Respiratory Syndrome related Coronavirus (SARS-CoV)
- Human Corona Virus NL63
- Human corona virus HKU1
- Middle East Respiratory Syndrome related Coronavirus (MERS-CoV)
- Novel Corona virus (COVID-19)
Asides SARS, MERS and the Novel Corona virus, the other corona viruses listed above are implicated in the common cold and are constantly and continually being transmitted across the human population globally with no serious debilitating consequences.