Covid-19 has spread around the planet, sending billions of people into lockdown as health services struggle to cope. The Health Ministry has confirmed 3,374 cases of coronavirus in India and 77 deaths so far. The disease has already claimed over 65,000 lives globally and infected close to 1,200,000 worldwide. The WHO has declared the coronavirus outbreak as a pandemic.A pandemic describes an infectious disease where we see significant and ongoing person-to-person spread in multiple countries around the world at the same time. The last time a pandemic occurred was in 2009 with swine flu.

What are coronaviruses?

Coronaviruses are a group of related viruses that cause diseases in mammals and birds. In humans, coronaviruses cause respiratory tract infections that can be mild, such as some cases of the common cold (among other possible causes, predominantly rhinoviruses), and others that can be lethal, such as SARS, MERS, and COVID-19. The most well known of these coronaviruses is SARS-CoV (“severe acute respiratory syndrome”), which in a November 2002 to July 2003 outbreak spread around the world and resulted in over 8000 cases and 774 deaths, with a case fatality rate of around 9–11%. In 2012, a novel coronavirus, MERS-CoV (“Middle East respiratory syndrome”), causing severe respiratory symptoms was identified. MERS has resulted in fatalities comparable to SARS, however the transmission route of MERS is very different. Whereas SARS was efficiently spread from one human to another, human MERS infections were generally a result of independent zoonoses (animal to human transmissions) from camels. 

Structure:

With a diameter of around 120nm, the virus appears as a large pleomorphic spherical particle having bulbous surface projections. The morphology of the virus includes four main structural proteins- a viral envelope (E); the spike (S), which forms the club-shaped protrusions; membrane proteins (M) and the nucleocapsid(N), which are bound to positive sense single-stranded RNA genome in a continuous beads-on-a string type conformation. Using the structural proteins, the virus enters the host cells where it establishes an infection, replicate, assemble its genome and then releases its progeny out of the host cell by exocytosis.  The coronavirus has the longest genome of any RNA-based virus as a single strand of nucleic acid is roughly 26,000 to 32,000 bases long.

Types:

There are seven different human coronavirus. They were given the name coronavirus - corona meaning crown - due to the crown-like spike on their surface according to centers for disease control and prevention. The family of coronavirus has four known genuses, named Alphacoronavirus, Betacoronavirus, Gammacoronavirus , and Deltacoronavirus.  The first two only infect mammals, including bats, pigs, cats and humans. Gammacoronavirus mostly infects birds, while Deltacoronavirus can infect both birds and mammals.

Common human coronaviruses

• 229E (alpha coronavirus)
• NL63 (alpha coronavirus)
• OC43 (beta coronavirus)
• HKU1 (beta coronavirus)

Other human coronaviruses

• MERS-CoV (the beta coronavirus that causes Middle East Respiratory Syndrome, or MERS)
• SARS-CoV (the beta coronavirus that causes severe acute respiratory syndrome, or SARS)
• SARS-CoV-2 (the novel coronavirus that causes coronavirus disease 2019, or COVID-19)

Several coronaviruses utilize animals as their primary hosts and have evolved to infect humans, too. Precursors to both SARS and MERS coronaviruses appear in bats. The SARS virus jumped from bats to civets (small, nocturnal mammals) on its way into people, while MERS infected camels before spreading to humans. Evidence suggests that the novel coronavirus also jumped from bats to humans after passing through an intermediate carrier, although scientists have not yet identified the infectious middleman creature.