Coronavirus is not a new-born virus, but has been around for many years in animals in an inactive form. It is a large family. Many strains of the family express common symptoms like cough, fever, sore throat, and sniffles. The symptoms range from mild respiratory disorders to severe respiratory complications. SARS– severe acute respiratory syndrome, is among the diseases caused by this family. The Coronavirus responsible for the ongoing pandemic is SARS-CoV-2, it causes COPD– chronic obstructive pulmonary disorder.
Types of coronavirus
Scientists divided coronaviruses into four sub-groups– Alpha, Beta, Gamma & Delta. Seven of these can infect us.
- 229E (Alpha)
- NL63 (Alpha)
- OC43 (Beta)
- HKU1 (Beta)
- MERS (Beta)
- SARS (Beta).
- SARS-COV-2, responsible for the pandemic.
The activity of the virus in the human system
In the event of any infection, the virus tries to enter the human cells and make copies using our replication and translation machinery. Meanwhile, our immune system recognizes its antigens and acts against it. SARS-CoV-2 can escape our immune response, which makes it unique.
It replicates calmly in a dormant stage, and hence the incubation period is long. After it makes several copies, our system recognizes it, but until then, it has already made copies ready to attack all our cells.
The genetic material of SARS-CoV-2 is RNA. Since RNA is single-stranded, it can undergo several mutations, making it challenging to make a vaccine. These mutations are random.
Theory and journey of different strains of SARS-CoV-2
Research suggests that there are minute differences between the various strains and thus exhibit ranging symptoms. The University of Bologna conducted vast research studying around 48500 different genomes of the virus. Then, they mapped its journey through different continents. A researcher explains that SARS-CoV-2 is already optimized, and the viable vaccine could provide immunity against various strains as well.
The journey of the virus
Currently, there are six strains. The first is the ‘L’ strain that appeared in Wuhan. Its mutated form is the ‘S’ strain (in early 2020). Besides, it can pick up different mutations in different geographical regions. These mutations made it more transmissible.
Until mid-January 2020, they observed strains V and G, among which G was more widespread. Its mutated forms are GR and GH, appearing at the end of February 2020. They can undergo two unique mutations that change the RNA polymerase and spike protein of the virus, facilitating its easy transmission.
The study suggests that GR is widespread in Europe, Italy, and North America, whereas GH is in France, Germany, and South America.
In Asia, the ‘L’ strain appeared initially, followed by the increasing prevalence of G, GH, and GR, which are also increasing worldwide. The L and V strains have started to disappear.
L and S strains of SARS-CoV-2
Initially, a scientist at the State-run Biotechnology Research Centre claims that Novel Coronavirus under research was found to be the ‘L’ strain. The dominance and prevalence of the more virulent L-type as compared to the ‘S’ type, could be the reason behind high mortality. The ‘L’ & ‘S’ strains primarily differ in the number and percentage of mutations that occur.
Since L can decode its entire sequence, the mutation rate is high and hence is more dangerous. Moreover, the L strain replicates quickly in short periods, infact, ten times as fast as ‘S’. That is why the ‘L’ strain of COVID spreads faster than the ‘S’. Since the immune system weakens with age, the mutation rate of the strain can easily affect the old.
‘L’ strain undergoes proofreading many times to ensure high fidelity of replication. The mutations during viral ‘L’ strain replication has minimal effect on humans with no functional significance of infection (incubation period).
A virus with an advantageous mutation spreads rapidly between people (higher transmissibility), and is not well recognized by the immune system (lower antigenicity). It also enables the virus to escape medication i.e., a virus with high drug resistance.
Mild and severe strains of SARS-CoV-2 with symptoms
We know that few people exhibit mild, or moderate, or severe symptoms. Mutation and proofreading of the virus is a reason.
Mild symptoms
Statistics show that 80% of Covid-19 cases are mild. Here, when the ‘L’ strain of COVID is in the initial stages of replication, it exhibits symptoms like dry cough, fever, and body aches. It might take a few days before you have a fever. Meanwhile, the ‘L’ will mutate itself and undergo proofreading thrice.
Moderate symptoms
As the ‘L’ strain undergoes multiple replications and mutations, it also proofreads 5-6 times. Moderate cough, high fever, breathing difficulty, and dehydration are the effects of viral activity in this stage. Sometimes the moderate stage can also progress to mild pneumonia, leading to secondary infections.
In the event of ‘S’ strain infection, you may express the symptoms for a short period, which disappears later. Since the number of enzymes required for replication are less, it can’t replicate as aggressively as the ‘L’ strain.
Severe symptoms
One in every five patients enters the last stage of the infection, experiencing severe symptoms. About 14% require respiratory support, and 86% can go into septic shock, i.e., drop in BP, leading to strokes, heart and lung failure, leading to death.
SARS -CoV-2 and human genetics (Genetic susceptibility)
Genetic sequencing studies on a large number of subjects could point to the underlying cause. Genetic factors also play a vital role in human susceptibility to infectious disease.
Most people experience mild symptoms of the infection with SARS-CoV-2, but a minority will express a severe life-threatening response. The human genome can answer a few questions. The genome is the instruction manual containing all the information needed to make, maintain, and repair. Variations in the human genome involved in the immune system, and others could explain some of the differences in response to COVID infections.
Genes within the genome can work singly, but more commonly act together. Human genes involved in response to infection are highly diverse within the genome. Some are located on the ‘X’ chromosome, and this could be one of the reasons why males (single X) are severely affected by Covid-19 than females (XX).
Whether genes turn out to play a major/minor role in determining the response to an infection, tracking them down is very important because they could provide clues about the biological pathways involved in the pathogen metabolism.
One promising place to look for genetic factors controlling Covid-19 is within the HLA (Human Leukocyte Antigen), which plays a crucial role in regulating immunity. There are many HLA types controlled by multiple genes.
