Corona: Back to the Basics

The exact time of origin of Covid-19 or the Corona virus is unknown. Between mid-November 2019 and December 2019, a large number of supposedly pneumonia cases were first noticed in the province of Hubei, China , especially in Wuhan city. The patients mostly presented themselves to the hospitals/clinics with fever, cough and shortness of breath. The rapid increase in the number of cases with these symptoms was very unusual. About 5 per cent of the patients, who came with these symptoms, were critically ill, and about half of them needed ventilator support. It was observed that the majority of patients were also over the age of 60 years with mortality rate increasing with age. On further investigation and research, which is still in nascent stages and ongoing across the globe at a great pace, it has been found that Covid-19 is actually genetically very similar to SARS-Corona virus (SARS-CoV) of 2002 and, therefore, named SARS-CoV-2. It is hypothesized that the mutation of SARS-CoV to SARS-CoV-2 is most likely to have happened between bats and pangolin, before infecting humans. Nothing is certain at this time.

To the best available medical understanding at this time, the spread of the novel Corona virus is through droplet transfer from nose and mouth, which are generated by coughing, sneezing, speaking and/or similar such activities, including spitting. It transfers via close personal contact such as touching, and fomite transmission, such as by objects/materials which are likely to carry infection. It has also been reported that asymptomatic carriers of the disease (people who show no symptoms but are Covid-19 positive) can transmit the disease from one person to another.

The reproduction number (R₀) of the virus is reported to be between 1.5 and 4. The reproduction number indicates the expected number of secondary cases produced by a single infected person in a population. For reference, the R₀ of the common flu is 1.4.

The incubation period of the virus is between 1 and 14 days. However, in some cases, the symptoms have been noticed after a period of 30 days as well. The virus can infect human beings of all ages.

However, so far, the prognosis has been really bad for infected people with co-morbidities like chronic obstructive pulmonary disease (COPD), diabetes (DM), hypertension (HTN), coronary artery disease (CAD), chronic kidney disease (CKD), any immunodeficiency (like in HIV/AIDS, cancer) etc. as compared to otherwise healthy individuals. Current tests available to help diagnose Covid-19 are rtPCR (reverse transcriptase polymerase chain reaction), chest CT (computed tomography), chest x-ray and CBC (complete blood count).

As of May 9, 2020, there is no specific treatment for Covid-19. However, there are certain experimental, repurposed medications that are being tried in extremely critical cases only under strict medical supervision as a last resort. In addition, a very large number of ‘candidate’ vaccines have been identified and, at least, 2-3 of them have entered clinical trial phase-1 in different countries. Depending on the outcome, next cycles of clinical trials shall be undertaken. If everything goes well as per expectations, a vaccine could become a reality, which is the only weapon against this novel Corona virus.

It is important to note that, unfortunately, these hypothetical medications are not specific treatments for Covid-19, as yet. Likewise, availability of an effective vaccine against the novel Corona virus, though highly desirable, is still a distant dream. More research, clinical trials and global efforts are continuing in this direction.

Common Q&A:

1. When was Corona virus discovered? The name indicates that the human race already encountered it in the past. How was it dealt with then?

To our knowledge, the Corona family of viruses were discovered almost 80-90 years back. The name ‘Corona’ comes from its structure which resembles a ‘crown’, as the virus envelope (outer surface), has spiky structures loosely resembling a crown. It is a large family of viruses effecting birds, mammals etc., including human beings. Infection of this family of virus causes variable respiratory illness in human beings, which we commonly call ‘common flu, fluor influenza’.

Six different types of corona viruses were already known to infect humans so far, each causing its own extent of medical conditions from mild to severe. They have always been dealt with within the realm of medical science available at the time when it happened. This is a seventh variant of the virus – a ‘novel Corona’.

• What is the percentage resemblance or difference in the genomic makeup of the earlier variants of ‘corona’ and the ‘novel ‘Corona’ virus strains?

As the latest strain of Corona virus, the novel Corona virus/SARS-CoV-2, is a new type or variant (only a few months old), not much is known and understood about it. So it is difficult to compare it with its older variants.

However, this class of virus is a single-stranded RNA virus, with a small genome (about 30 kNT).Very characteristic about it is – and applies to all RNA viruses – that it mutates faster than, say DNA viruses, and, hence, newer variants get formed at a faster pace than DNA viruses.

• There  has been suggestions of different strains in different countries. Is the mutational machinery of the virus so prompt, fast and ‘smart’? What is the mutational rate of other known viruses in general?

Yes, this appears to be the case based on whatever limited information is available at this point in time from different labs in different countries, including NT sequencing results from India. As we said earlier, in the absence of credible and reproducible results on Covid-19 from different countries, it would be premature to conclude anything at this time point. In our opinion, however, high and low rates of mutation of DNA and RNA viruses, respectively, is nothing to do with being ‘smart’ or not. It is to do with the life machinery used to ‘replicate’ the viral genome. DNA viruses use ‘DNA polymerase’ for replication that has high fidelity (less errors), while RNA viruses use ‘reverse transcriptase’ for the same purpose that has low fidelity (more errors).The two processes have different characteristics and that influences their rates of mutation. 

• In plasma therapy, would the plasma of the recovered people be more effective and beneficial, and how does it work?

Only a few such clinical evidences are available till today. Therefore, it’s an experimental medicine only and not a specific treatment for Covid-19. It appears to have helped very critical patients. The blood plasma of a person recovered recently from the Covid-19 viral infection is likely to be rich in anti-body against the virus. If that enriched plasma is transfused into another person, who is critically suffering from Covid-19 infection, the person will get a booster of anti-body present in the plasma and help the patient’s recovery. However, the WHO has made it clear that, as of now, there is no scientific proof that a person who has recovered from Covid-19 is permanently immune to it.

• Do you think we need anti-body screening for SARSCoV-2?

Antibody test is quick and much less technical as compared to rtPCR test, which is time consuming and more technical. While the rtPCR test is definitive indicating presence of the viral genome, anti-body test is indicative of the viral infection. So, depending on the need, the test methodology has to be chosen. If the purpose is to screen the population or a population group for active infections, rtPCR is the test. On the other hand, antibody test can be done if we want to screen the population to know who could be or was previously infected. But, if we want a confirmatory diagnostic test, we shall eventually need artPCR test.

• Do you think asymptomatic people can spread the virus? How can we stop the spread?

All asymptomatic people can spread as much virus as a symptomatic person can. As we have no vaccine against this virus, the only options left to humanity is to break the chain of spread of the virus from the suspected person(s).

Effective options for this are: (a) quarantine of suspected person, (b) isolation of confirmed patients (including appropriate medical interventions when needed), (c) strict social distancing, (d) home stay, (e) strict coughing etiquette, (f) complete prohibition on spitting, (g) strict maintenance of personal hygiene, especially hand hygiene, among other measures that are currently in force across the globe, including measures implemented by various governmental agencies in India. We have no other option at this time.

• How does the virus spread in a population very fast?

As per all medical and scientific evidence available at the moment, the transfer of Covid-19 from one person to other is only through contact involving ‘droplet’ transfer. Covid-19 is highly infectious (one person may infect an estimated over 400 people in 30 days!), the spread from one infected person to another or a group of persons could be extremely widespread if the cycle continues. So, if  person A has tested positive for the virus (being either symptomatic or asymptomatic) and has come in contact with person B (or a group of people) in a way that ‘droplet’ transfer could have happened, person B (or the group of people) have high probability to acquire the infection. All these people need to be observed/quarantined/isolated, as the case may be, to be abundantly cautious.

• Not many tests have been done. Do you think that the possibility of asymptomatic cases can be there, which can be more dangerous?

Yes, this fear is always there. WHO recommends widespread SARS-Cov-2 testing to the maximum extent possible – something like screening of the population, done by some countries. With that we shall be able to get the real picture of the spread of the virus in the population. Otherwise, as WHO has been warning lately, a follow up surge in infection might come in the near future.

Disclaimer: SARS-CoV-2 or Covid-19 is a novel form of Corona virus about which we have learnt only a few months back. Therefore, the available knowledge/information is limited. More investigation is ongoing into the disease as well as on the virus to understand it better. Due to Covid-19’s novelty, the understanding of the progression of the disease, it’s symptoms and it’s virology are open to change as we understand them better.

with inputs from Dr R.N Sharan