For most people, the lucky 81%, Covid-19 is an extreme case of bad flue with extreme headaches and a deep feeling of exhaustion accompanied by cough and fever.
It sometimes may be supplemented by a feel of loss of taste or smell. For some, the attack is so weak, and their natural reaction is so strong, that they present no symptoms. They are known as asymptomatic cases. For others however, the other 19% the disease progresses inside the body and worsens, as the various defense mechanisms such as the innate or the adaptive immune fail to produce enough troops to fight the invader, which continues to multiply at a higher rate than the natural defense system can produce enough counter measures. They require hospitalisation For the very unlucky 3 odd %, it is death at the end of a solitary agony.
Initially, clinicians associated the virus to that of SARS and MERS and perceived that, even though less deadly, it would in its most extreme version be an acute respiratory disease where the virus persistent attack on the lungs degenerates from a severe pneumonia into acute respiratory distress syndrome (ARDS).
It would have to be fought in the advanced stages with respiratory assistance, hence the race to secure enough respiratory machines known as ventilators that could compensate for the deterioration of the lungs, while palliative therapeutics could be administered in the form of antiviral drugs to annihilate the enemy, anti inflammatory drugs to limit overproduction of cytokines and antibiotics to fight off the associated infections. Autopsies however have revealed that the disease progressed way beyond the lungs into the heart and kidneys and in general through the cardiovascular system as evidence of blood clotting was observed, drawing a picture of multi organ failures.
As a large number of old people that were infected died, it was thought that older people were the only people at risk because of their weakened defense immune systems due to old age and underlying conditions prevailing in older people such as hypertension, overweight, diabetes and other afflictions. However, as the spread of the disease increased, it was found that younger people were also dying, some due to underlying conditions or unhealthy living habits and some falling down under no perceivable cause.
At the time of writing almost 27 million cases have been reported and about 3% have died. This public health emergency has fuelled a quest for a common better understanding of the ramification of the disease and improved therapeutics, has energized research worldwide and over 7000 papers have been published in electronic form prior to official pear review
Clinicians are realizing that although the lungs are ground zero, its reach can extend to many organs including the heart and blood vessels, kidneys, gut, and brain. To understand better the extent and possible ramifications of the disease one has to understand that the virus S proteins that are protuberant over its core seek to attach themselves to a cell surface receptor ACE2 , standing for angiotensin-converting enzyme 2, which helps regulating blood pressure.
These receptors are not only present in the linings of the nose, the lungs the kidneys and the lining of our endothelial stroma better known as the stomach gut but also are present in our entire cardio-vascular system. Moreover, the particularly small size of the virus (about70 Manometers) enables it to permeate from tissues into the smallest capillaries hence the ability of the virus to reach any of the weakest parts of one’s anatomy.
Without going into details, we will attempt to schematize the various successive stages contingent to the progression of the disease, without describing in detail the sequence of the defense mechanisms of our immune system. (readers might want to consult articles “Our immune System” of the 24thof may and ”Vaccines” of the 9Th June).
As we said above, as the respiratory tract, the cardio vascular system and part of the gastro-intestinal tract are lined up with ACE2 receptors of which the virus spike S proteins are so fond for the ACE2 receptor, the pathologies can evolve differently on various individuals depending on various factors. As it is a battle between the virus and our defense soldiers, the robustness of our immune system is the prime determinant in the severity and duration of the pathology.
However, depending on the degree of exposure of an individual to the virus the harshness of the attack will vary even with the same sturdiness of the immune system. Just like depending on the intensity of radiation an individual will be more or less affected, people receiving an in intense initial viral load or receiving repeated exposure like front line workers or doctors are more likely to face a severe bout of the infection.
People with serious respiratory problems are also in the first line. In addition, as the ACE2 receptor plays an important role in the blood pressure regulation system and the presence of the virus in the blood tempers with the orderliness of the system. This makes people with underlying conditions such as obesity, high blood pressure, serious heart problems, kidney problems or diabetes and in general, people that receive medication that is related to blood pressure more susceptible to face critical situations sometimes resulting in death.
We have drawn a conceptual chart designed to illustrate the main pathological phases in the progression of the disease. As described above the age, the additional pathologies may change the actual incubation period. For incubation, the asymptotic and the mild cases we have taken a mean value whereas for the more advanced developments we have taken a range which especially in case or aged patients and those with underlying conditions can develop more rapidly and result n a more rapid death.
In further articles we shall attempt in as observers to navigate through some of the various mechanisms that appear to be at work during the progressive stages of the pathology.
|By Digenis||8 September 2020|