Human coronaviruses are everywhere and were cultured in the 1960s from nasal cavities of people with the common cold, reports a recent study. Coronaviruses are the 2nd leading cause of the common cold after rhinoviruses.
There are four main sub-groupings of coronaviruses, known as alpha, beta, gamma, and delta. Both the Middle East Respiratory Syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS) are betacoronavirus and have their origins in bats.
Both MERS (ongoing) and SARS (2004) have been known to cause severe illness in humans.
Betacoronaviruses are microscopic balls covered in spikes that encapsulate a central core of genetic material. The virus must infect cells to replicate and do this, and it must first attach to the cells.
People commonly get infected with human coronaviruses 229E, NL63, OC43, and HKU1, say the U.S. CDC.
On January 9, 2020, China's CDC reported a novel coronavirus as the causative agent of the new coronavirus outbreak, which is phylogenetically in the SARS-CoV clade. This novel coronavirus has been named ‘severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), while the human disease it causes has been classified by the WHO as COVID-19 disease.
The current outbreak of novel coronavirus SARS-CoV-2 originated in 2019 but has now spread internationally, impacting an increasing number of countries. According to previous studies, reported illnesses have ranged from mild to severe, resulting in fatalities.
Airborne transmission via droplets and aerosols enables some of these coronaviruses to spread efficiently among humans, causing outbreaks difficult to control. Because viruses spread by small particle aerosol do not require close contact, the infection source may not be evident.
These small particles can be inhaled by susceptible persons in the same room or are capable of more distant spread as they are carried in air currents, says the U.S. CDC.
On February 5, 2020, JAMA published a new study from genetic sequencing data, showing this coronavirus shares 79.5% of the genetic sequence with SARS-CoV-1 and has 96.2% homology to a bat coronavirus. This indicates SARS-CoV-1 and SARS-CoV-2 are not the same coronaviruses.
A study published on July 7, 2020, concluded by saying 'it is now established that SARS-CoV-2 pre-existing immune reactivity exists to some degree in the general population. It is hypothesized, but not yet proven, that this might be due to immunity to common cold coronaviruses.'
'This might have implications for COVID-19 disease severity, herd immunity, and vaccine development, which still awaits to be addressed with actual data.'
SARS-CoV-1 was the first major novel infectious disease to hit the international community in the 21st century, says the U.S. CDC.
SARS was first reported in Asia in February 2003 and became a notifiable disease in mid-April in central China. As of July 2003, the WHO reported 325 cases, and the illness spread to about 24 countries in South America, Europe, and Asia during 2003.
The emergence of the betacoronavirus Middle East Respiratory Syndrome (MERS) was first reported in the Kingdom of Saudi Arabia in 2012.
Humans are infected with MERS-CoV from direct or indirect contact with dromedaries. MERS-CoV has demonstrated the ability to transmit between humans. So far, the observed non-sustained human-to-human transmission has occurred mainly in healthcare settings, says the WHO.
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Note: This content is sourced from the U.S. CDC, the WHO, research studies, and is reviewed by health professionals, such as Dr. Robert Carlson.