Coronaviruses

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Original Editor - Lucinda hampton

Top Contributors - Lucinda hampton and Rishika Babburu  

Introduction

Coronaviruses are a family of viruses known for containing strains that cause potentially deadly diseases in mammals and birds. In humans they're typically spread via airborne droplets of fluid produced by infected individuals. Scientists have known of the human coronavirus since the 1960s. But only rarely has it garnered wider recognition over the past half a century.

During the mid-1990s these viruses were described as the backwater of virology, since none caused serious disease in humans. However, this changed in 2002-03 with the emergence of a coronavirus causing severe acute respiratory syndrome (SARS-CoV), and then in 2012 the Middle East respiratory syndrome coronavirus (MERS-CoV) in Saudi Arabia. The origin of both viruses was thought to be in bats, with civet cats and dromedary camels being the confirmed zoonotic reservoirs for SARS-CoV and MERS-CoV, respectively.

All coronaviruses are zoonotic. They start off in animals and can then, following mutation, recombination and adaptation, be passed on to humans.

The International Committee for the Taxonomy of Viruses has approved the naming of more than 40 coronaviruses. The vast majority of these infect animals.

• The COVID-19 outbreak has brought the number of identified coronaviruses that infect humans to seven.
• Four of these are community acquired and have circulated through the human population continually for a very long time. The four community-acquired human coronaviruses typically cause mild cold-like symptoms in humans. Two of them, hCoV-OC43 and hCoV-229E, have been responsible for between 10% and 30% of all common colds since about the 1960s.
• Three of these (SARS-CoV, MERS-CoV and SARS-CoV-2) appear to have jumped to the human population more recently. Worryingly, these three result in a high mortality rate.

Name Origin

First described in detail in the 1960s, the coronavirus gets its name from a distinctive corona or 'crown' of sugary-proteins that projects from the envelope surrounding the particle.

• Encoding the virus's make-up is the longest genome of any RNA-based virus – a single strand of nucleic acid roughly 26,000 to 32,000 bases long.

There are four known genuses in the family

• Alphacoronavirus, Betacoronavirus: only infect mammals, including bats, pigs, cats, and humans
• Gammacoronavirus: mostly infects birds such as poultry
• Deltacoronavirus: can infect both birds and mammals.

Symptoms

Coronaviruses can give rise to a variety of symptoms in different animals.

In a high percentage of cases, infection causes no symptoms at all. These individuals can still easily spread the virus without knowing they're infected.

While some strains cause diarrhoea in pigs and in turkeys, in humans infections are usually compared to a bad cold, causing mild to moderate upper respiratory problems such as a runny nose and sore throat.

There are a handful of lethal exceptions, which have had a devastating impact on livestock and human health around the globe. Symptoms in these cases tend to start with a sore throat and fever.

Coronaviruses in Animals

Coronaviruses have been around for many years. They include viruses contributing to a variety of animal and avian coronaviruses, such as infectious bronchitis virus (IBV), which infects poultry. Coronaviruses typically cause respiratory or gastrointestinal illness, but strains of IBV have been shown to target the oviduct in chickens, and others can cause severe kidney disease.

Animal and avian coronaviruses can have high mortality rates among infected animals and illustrate the difficulties in developing vaccines.

Similar to influenza viruses, despite many decades of research there is no vaccine that protects against all strains of infectious bronchitis virus (IBV) coronavirus.

This is due in part to the continuously shifting diversity in the virus spike glycoprotein, a major immunogenic target and hence a good vaccine candidate for animal and human infections.

During the mid-1990s these viruses were described as the backwater of virology, since none caused serious disease in humans. However, this changed in 2002-03 with the emergence of a coronavirus causing severe acute respiratory syndrome (SARS-CoV), and then in 2012 the Middle East respiratory syndrome coronavirus (MERS-CoV) in Saudi Arabia. The origin of both viruses was thought to be in bats, with civet cats and dromedary camels being the confirmed zoonotic reservoirs for SARS-CoV and MERS-CoV, respectively.

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