A Primer on the Coronavirus


 Human coronaviruses (HCoVs) are nothing new. Their existence has been known for decades and, until the 21st century, they were considered inconsequential pathogens, responsible for up to 30% of cases of the common cold. However, all this changed starting in 2002. Cases of severe atypical pneumonia were described in Guangdong Province in China. This new disease became known as severe acute respiratory syndrome, or SARS. A beta-HCoV named SARS-CoV, was identified as the causative agent. Early cases shared a history of human-animal contact at live game markets in China, leading experts to suspect a zoonotic transmission, meaning animal to human transmission. While SARS caused a worldwide panic, similar to what is being seen today, few cases were identified outside of China and the panic finally abated as the disease did.

Once again, in December 2019, China identified another novel coronavirus, 2019-nCoV (aka COVID-19), which arose in the live game markets, this time in Wuhan. Mounting cases and deaths caused China to impose an unprecedented cordon sanitaire, meaning a guarded area where no one is allowed to leave. As of the end of February, China reported over 75,000 cases and 2,700 deaths. Cases are being reported in other countries, but with a few exceptions, all have been traceable back to China. The death rate at present is 3%, as opposed to 1% for most annual influenza, or flu, cases. Another pathogenic beta-CoV epidemic occurred in 2012 in Saudi Arabia. This virus, which made the species jump from animal to humans, again associated with live animal markets, was called Middle East respiratory syndrome, or MERS. Fortunately, MERS remained localized and did not cause a panic.

These mutated coronaviruses cause lower respiratory symptoms (lung infections like pneumonia), because the human receptor for the virus, angiotensin-converting enzyme 2 (ACE2), is found primarily in the lungs, not the upper airway. That is why there are few upper respiratory symptoms like a runny nose, sore throat, and dry cough. The virus heads directly for the lungs. As is seen with the flu, the very young, very old, and those with chronic illnesses are most susceptible.

When dealing with 2019-nCoV, it is important to keep things in perspective. The flu infects millions in this country every year, and on average it causes between 20-50,000 deaths every year. The flu is a much more existential threat to Americans than coronavirus. While it is important to take steps like closing the border and placing potentially exposed persons in quarantine to protect American lives, 2019-nCoV is very unlikely to cause anything like what we face from the flu every year. The wild panic being seen is certainly uncalled for and overreactive, to say the least.

Finally, one must wonder how the usually tame coronavirus mutated on three separate occasions into a much more virulent viral strain. Two of the three known outbreaks originated in China, and China has one main microbiology and virology lab, which is located in Wuhan. Did the virus mutate naturally, or did it get help? We will probably never know.

By Peter Galvin, MD