Revising What Makes Covid-19 Special: It’s Not Blood Clots
By: Shin Jie Yong
Tags: Technology, Health, Covid 19, Life, Science

Revising What Makes Covid-19 Special: It’s Not Blood Clots

Infections come with blood clots — be it SARS, MERS, or other pathogens. So, what really makes Covid-19 special?

We know that Covid-19 kills by pneumonia and coagulopathy. Pneumonia means lung infection, particularly in the air sacs, that obstruct gas exchange and breathing. Coagulopathy means blood clotting disorder that comes by different names depending on where the clot happens.

In Covid-19, scientists have seen cases of pulmonary embolism (artery blockage in the lungs), alveolar capillary microthrombi (small blood clots in air sacs), deep venous thrombosis (blood clots in veins deep in the body, usually in legs), multi-organ endotheliitis (inflamed blood vessels), multi-organ microthrombi (small blood clots), ischemic infarcts (artery blockage near the brain), and perhaps more.

These medical terms are nothing but coagulopathies. Among these, deep venous thrombosis (DVT) is arguably the most relevant as it usually precedes pulmonary embolism (PE). Scientists often lump them together as DVT/PE. And DVT/PE the most common type of Covid-19 coagulopathy. It happens in about 25% of Covid-19 cases in the ICU. In contrasts, the usual prevalence of DVT/PE in non-Covid-19 ICU cases is at <2%.

Therefore, there has been a widespread recognition in the scientific literature [refs 1, 2, 3, 4, etc.] and news outlets that Covid-19 is a disease of the blood vessels. Coagulopathies are the driver of the multi-organ complications in severe Covid-19, we all think. It makes Covid-19 one particular kind of disease that can attack the blood vessels. At least I have previously written about it here:

While it is true that Covid-19 causes coagulopathies that hit distant organs, it is not what makes Covid-19 unique from other diseases. Here are a few reasons why:

These points clarify that Covid-19 is a respiratory disease that occasionally comes with coagulopathies that affect other organs. In other words, Covid-19 is not a blood clotting disease, but pneumonia that may come with blood clots.

So, what makes Covid-19 special?

It is not blood clots as it is a general characteristic of pneumonia or infections. It is not the incubation period (i.e., the duration between the first viral exposure and symptom appearance) as it is similar for all SARS, MERS, and Covid-19. It is not the propensity to affect almost every organ in the body as most systemic diseases are like that. It is not the ability to cause lingering symptoms for weeks to months, even in discharged patients, as other infections can do that.

These may be anticlimatic, but evolution does not magically build an entirely new distinct biological entity after all. Evolution works by modifying existing biological constructs. Hence, Covid-19 must also be viewed in light on other viruses (or pathogens).

In reality, Covid-19 is not very deadly with a case fatality rate of about 1%, compared to 9.7% and 34% of SARS and MERS, respectively. But Covid-19 is much more lethal to the older age groups, black people, and individuals with multiple medical comorbidities. Nearly half of infected people do not show symptoms, yet they can transmit the virus to others. Also, Covid-19 is highly contagious owing to its efficient binding capacity to the host ACE2 receptor.

Thus, the silent and efficient human spread — coupled with overpopulation, growing ageing population, increasing prevalence of medical comorbidities, international travel, poor infection control policies, and social inequalities in some countries — make Covid-19 successful.