Coronaviruses: New to Humanity but Not New to The World

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Although many of us might not have heard of coronaviruses before 2019, these viruses are not new to the world. They belong to a large family of hundreds of viruses that have been on scientist’s radar for a long time. Most of these viruses reside in animal reservoirs like pigs, camels, bats, or cats. Despite the world’s familiarity with different types of coronaviruses, COVID-19 is known as a “novel” coronavirus. This means that, although this virus has existed in animals for some time, it has only recently been identified through an animal-to-human transition.

All coronaviruses are separated by scientists into four distinct groups: alpha, beta, gamma, and delta coronaviruses. Only seven alpha and beta coronaviruses are known to infect humans. Scientists have named these viruses:

  • 229E (alpha coronavirus)

  • NL63 (alpha coronavirus)

  • OC43 (beta coronavirus)

  • HKU1 (beta coronavirus)

  • MERS-CoV (beta coronavirus that causes MERS)

  • SARS- CoV (beta coronavirus that causes SARS)

  • SARS-CoV-2 (novel coronavirus that causes COVID-19)

Of these seven, four of the viruses are reported to cause mild to moderate symptoms and three are associated with serious diseases. The first identified coronaviruses were recorded in the mid 1960s, but are believed to have circulated in human systems for centuries. These include 229E (alpha coronavirus), NL63 (alpha coronavirus), OC43 (beta coronavirus), and HKU1 (beta coronavirus). This group of viruses are known to present only mild respiratory infection, though HKU1 is associated with gastrointestinal infection as well.

The three viruses known to lead to potentially fatal diseases are SARS-CoV, MERS-CoV, and SARS-CoV-2. SARS-CoV is known to cause severe acute respiratory syndrome (SARS), and the virus infected a total of 8,098 individuals during the outbreak of 2003. MERS-CoV causes Middle East respiratory syndrome (MERS), and the 2012 outbreak continues to infect dozens of people annually. SARS-CoV-2 causes the coronavirus disease the world is currently dealing with in the COVID-19 pandemic.

Just as MERS was transmitted to humans from the animal reservoir camels, COVID-19 is believed to have similarly originated from an animal reservoir, though specifically which one is still being studied. This “jump” of a virus from an animal reservoir to humans is called a spillover event. A spillover event can occur either through a mutation directly to humans or through an intermediary species that mutates the virus into a human pathogen.

Although the family of coronaviruses has been around for some time, there is still much to learn about this new novel coronavirus. This global pandemic has proven to infectious disease researchers that there is still much to be learned about spillover events in order to better equip society to handle possible animal-to-human transmissions from viruses in the future.

Resources:
Cleveland Clinic: https://consultqd.clevelandclinic.org/coronaviruses-have-been-around-for-centuries-what-differentiates-2019-ncov/
National Institute of Allergy and Infectious Disease:
https://www.niaid.nih.gov/diseases-conditions/coronaviruses
WebMD: https://www.webmd.com/lung/coronavirus-strains#1