SARS-CoV-2 virus & infection it causes

Part - II

Padmashree Dr Ravi Kannan

Director, Cachar Cancer Hospital and Research Centre, Silchar

This virus does not spread through newspapers, currency notes, fruits and vegetables or grocery packages

Coronaviruses are a large family of viruses residing in birds and mammals of which seven are known to cause human illnesses ranging from the common cold to more severe diseases like Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS). They are named for the crown-like spikes on their surface. Human coronaviruses were first identified in the mid-1960s. All viruses need the host cells that they infect in order to reproduce.

The new COVID-19 or SARS-CoV-2 virus spreads through droplets generated during coughing, sneezing, spitting and other similar acts. The force of cough propels these droplets containing the virus over a radius of as much as 25 feet. Individuals present in this area inhale the virus during breathing and will get infected. In addition, these particles will settle on surfaces of tables, door knobs, shelves and the like where they persist for variable periods of time. When our hands make contact with these surfaces, the virus gets transferred to the hands. When we scratch our eyes or nose or mouth without washing hands, the virus gains entry to our respiratory passages. Healthcare workers are at risk of acquiring infection from infected patients in the same way. Men are at a slightly higher risk because of the presence of extra ACE receptor to which the virus attaches in the human cells.

This virus does not spread through newspapers, currency notes, fruits and vegetables or grocery packages. It lingers for a few hours on paper and cardboard and for a few days on glass and plastic surfaces. Hands must be washed before handling food including grocery, fruits and vegetables. Fruits and vegetables must be washed in the usual manner before consumption. Packaging must be disposed and hands washed with soap.

The virus has an incubation period (number of days before symptoms appear following infection) of about 4 to 6 days (range of 1 to 14 days). All infected individuals can infect others even if they are asymptomatic. A significant number of individuals clear the virus after infection without developing any symptoms. Of all those who will develop symptoms, 80% will have mild symptoms like low grade fever, fatigue, sore throat, mild cough and sometimes diarrhoea. They may also have loss of taste or smell. Twenty per cent of individuals will develop symptoms severe enough to merit hospitalization, 5% of them needing ICU care. One per cent of all infected individuals could die as a result of the infection. If the medical facilities get overwhelmed, these numbers are likely to be higher.

The virus primarily affects the respiratory system and causes a form of pneumonia. This results in breathing difficulty, distress and ultimately respiratory failure with a potential of death. The virus also stirs up an immune storm in the human body which can affect practically any organ including the heart, central nervous system, kidneys, pancreas, liver, skin etc. In children, a peculiar immune complex mediated illness manifests several weeks after the respiratory illness subsides.

The virus is identified in the human body through a test called RT PCR (Reverse Transcriptase Polymerase Chain Reaction) or qPCR (real time Polymerase Chain Reaction). Swabs are taken from the nasopharynx (region behind the nose), throat or from the trachea and bronchi for this purpose. This test however identifies the virus only after the 4th or 5th day of infection. This means that in the first few days of infection, while the individual remains a source of infection for others, the test will show a false negative result.

After about a week of infection, the body starts manifesting an antibody response. The first antibody is called IgM which starts appearing by the seventh day, peaks by the 14th day and then slowly disappears. The IgG antibody starts to appear around the 14th day and gradually rises resulting in clearance of the virus from the body. The body also mediates a cell mediated response against the virus. The presence of the IgG antibody gives rise to the concept of immunity passports and to the idea of plasma therapy. Antibody testing in the community will give us an idea about the number of individuals who have been infected (both symptomatic and asymptomatic) and will help health officials plan care in the community.

Currently, definitive therapy is not available against the virus. Treatment is largely symptomatic and experimental. A preventive vaccine is also unavailable even though several vaccines are in different phases of trials and research. Lockdowns in different countries have helped stagger the number of infections over a longer period of time allowing the testing and healthcare facilities to prepare for the pandemic. They however do not cure the pandemic.

Development of herd immunity is essential for preventing infection in the community. The contagiousness or infection potential for any organism is defined by its reproduction number or R0 (pronounced R naught) in a situation where none of the exposed individuals has been vaccinated or exposed to the infection and there is no effective form of treatment available. The R0 indicates the number of people an infected person will in turn infect. A pandemic will decline and cease when the R0 falls below 1. Through the course of a pandemic, the R0 is dynamic and will rise or fall depending on several factors.

The R0 of the SARS CoV2 virus has been estimated to vary from 2.3 to 6.6 in different locations. In order for the community to develop adequate herd immunity, an R0 of 2.3 will need 56% of the population to have effective antibodies (to be immune) and if the R0 is 5, it indicates that 80% of the population will need to be immune to confer herd immunity on the community.

Immunity can be achieved by vaccination or by individuals getting successfully cured after getting infection. Vaccination is a safe way to promote herd immunity. On the other hand, promoting herd immunity by exposing the population to infection is a dangerous way to achieve this since this will entail a mortality risk of about 1%. Risk of severe infection and death is higher amongst the elderly, diabetics, individuals with cardiovascular and lung diseases including hypertension, stroke and chronic obstructive pulmonary diseases, smokers, obese and overweight individuals and those on cancer chemotherapy and radiation therapy. Surgery on individuals with COVID infection carries with it a higher risk of death.

There is no scientific evidence that alternative forms of treatment help prevent or cure the illness. The virus is not halted by changes in weather, drinking or gargling with hot water, liberal use of black pepper, mint, turmeric or other household remedies. Immune boosters against the virus are non-existent. Yoga or physical exercise or meditation of any form while recommended in general, have no special powers against the virus.

Five measures are important to reduce spread of the SARS-CoV-2 virus in the community. These include wearing masks every time anyone is outside home, meticulously practising social distancing, scrupulously observing hand hygiene and cough etiquette and voluntary testing and quarantining every individual with suspected infection. All of these will reduce the R0 of the infection and will help reduce spread of infected droplets from one individual to the other.