The 7 strains of coronavirus and unknowns of Covid-19

Quarantining a sick person is not enough if precautions are not taken to decontaminate surfaces that the patient came in contact with.

Though the number of coronavirus cases around the world has closed in on the 100,000 mark, and total deaths have crossed 3,300, the behaviour of the Sars-CoV2 virus that causes the Covid-19 disease is yet to be revealed.

A King County Metro equipment service worker sprays a Virex solution to sanitise buses against the coronavirus in Seattle, Washington, on Thursday.(Reuters Photo)

Scientists have identified seven strains of coronavirus that infect humans. These cause illness, ranging from common cold to more severe diseases such as Middle East Respiratory Syndrome or MERS.

The harmless strains of coronavirus are Serotype 229E, Serotype OC43, Serotype NL63 and Serotype HUK1. These cause symptoms of common cold and rarely cause severe pneumonia.

But the more dangerous strains are Sars-CoV which causes Severe Acute Respiratory Syndrome or SARS, Mers-CoV which Middle East Respiratory Syndrome or MERS and Sars-CoV2 that causes the coronavirus disease Covid-19.

Sars-CoV2 is closely associated to two bat-drived Sars-like coronaviruses (bat-SL-Cov-ZC45 and bat-SL-Cov-ZXC21) collected in 2018 in Zhoushan, eastern China. It has 79 per cent genetic affinity with Sars-CoV and 50 per cent with Mers-CoV.

The Sars-CoV2 receptor-binding domain structure, which allows a virus to latch on to and enter a cell, is similar to Sars-CoV, despite amino acid variation at some key residues. 

On smooth surfaces such as tables, phones etc, Sars-CoV retains its viability for five days at 22-25 degrees Celsius and relative humidity at 40-50 per cent, which is typical for air-conditioned room. Though this may vary for Sars-CoV2, experts say this is a good indicator for its behaviour.

It is clear, however, that the virus causes infection through respiratory droplets from an infected person. So, quarantining a sick person is not enough if precautions are not taken to decontaminate surfaces that the patient came in contact with, and on which coronaviruses can survive for several days.

Studies have also found the Sars-CoV-2 detectable in other body fluids and excreta, which makes it critical for people to keep their surroundings clean and frequently wash their hands with soap and water, or water alone.