How covid-19 infect lungs ?

While Covid 19 pandemic sweeps across the globe, it is important to understand the transmission and the effect of the virus which has made it a pandemic. Covid 19 belongs to the coronavirus family, which also includes the SARS virus (Severe Acute Respiratory Syndrome) and MERS (Middle East Respiratory Symptoms) virus. The family of Coronavirus includes virus strains that cause the common cold and flu.  

It has been found that Covid 19 is a close relative of SARS. SARS is a novel type of virus that was reported in 2007, and like most SARS viruses, Covid 19 affects the respiratory tract in humans. The infection starts off with mild flu-like symptoms or no symptoms, and further progress to severe symptoms.

Covid 19 primarily infects the lungs in the affected individuals and in severe cases causes’ death due to ARDS and pneumonia. It is important to remember that it does not lead to ARDS and pneumonia in all the cases, which is an occurrence in most severe cases.

In the majority of the cases i.e. 80% will exhibit mild symptoms, 14% will have pneumonia, 5% will suffer from septic shock and organ failure (mostly respiratory failure) and in 2% cases it will be fatal.

Some of the primary symptoms to look for in a Covid 19 infected person are fever, dizziness, breathlessness, headache, dry cough ( eventually result in phlegm) and in a few cases loss in smell and taste. A few cases have also reported diarrhoea and fatigue.

So while a person infected with Covid 19 can be cured, it is important to understand that the factors that lead to fatality, include underlying illnesses (hypertension, diabetes, cardiac problems, respiratory issues) and individuals who are on immune-suppressing medications. In older individuals, the risk is higher, as the immunity decreases with age and they have a higher disposition for other illnesses.

Another important aspect in understanding Covid 19 is its effect on the body system, especially the lungs.

Acute Respiratory Distress Syndrome (ARDS)

There is a direct correlation between Covid 19 and ARDS, severe cases of Covid 19 infection leads to ARDS and pneumonia, which can prove to be fatal for the infected individual. Acute Respiratory Distress Syndrome causes dry cough, heavy breathing, breathing difficulties and increased heart rate. In most healthy individuals, who do not have underlying issues Covid 19 exhibits mild symptoms, which can be treated with medications and eventually the patients recover. In severe cases, where the infected person has an impaired immunity due to underlying health conditions, an infection due to Covid 19 can progress to severe ARDS. Once the patient progresses to ARDS, it eventually leads to pneumonia.

Before understanding the severity of Covid 19 infection, it is important to understand the different stages/categories of Covid 19 infection:

First category: These individuals are infected by the virus, but act as carriers but may not exhibit the symptoms. These individuals are at a higher risk of spreading the virus as they might be oblivious to its presence.

Second category: Individuals with mild fever, cough, headache or possible conjunctivitis. This is due to an infection in the upper respiratory tract.

Third category: Similar to the third category, the symptoms here are more pronounced and might require hospitalization. Immediate treatment can help alleviate the symptoms and prevent a fatality.

Fourth category: Severe cases of Covid 19, might lead to ARDS and pneumonia. At this stage, it is fatal.

Effect of ARDS on lungs

Covid 19 directly impacts the lungs and damages the alveoli (tiny air sacs). The function of the alveolus is to transfer oxygen to the blood vessels. These blood vessels or capillaries carry the oxygen to the RBCs (Red blood cells). It is the RBCs that finally deliver the oxygen to all the internal organs in the body. 

The virus works by damaging the wall and the lining of the alveolus and capillaries. The debris from the damage, which is plasma protein accumulates on the alveolus wall and thickens the lining. As the walls’ thicken, the transfer of oxygen to the red blood cells is impaired. The thicker the wall gets, the more difficult it gets to transfer oxygen to the red blood cells, which causes difficulty in breathing as the body is running short of oxygen. And the lack of oxygen to the internal organs results in a deficit in the body and impairs the functioning of the organs. At this juncture, the body fights to increase oxygen intake.

And the first response of the body is to destroy the virus and prevent its replication, but if the individual has weaker immunity then the body is unable to stop the virus, and this aggravates the crisis

Pneumonia

As the air sacs are damaged, there is an influx of liquid which is mostly inflamed cells and protein and this fluid build-up leads to pneumonia. This further impairs the oxygen intake by the lungs and hinders the oxygen exchange. Due to the novelty of the Covid 19 strain, there is no immediate treatment to directly cure pneumonia in Covid 19 patients and are mostly given supportive care.

How do doctors’ ascertain the onset of ARDS in Covid 19 infected individuals?

There are some key indicators that the doctors to judge the onset and severity of ARDS in infected individuals:

Hypoxia – Low oxygen levels in the blood, due to damage to the alveolus

Breathing difficulties and shortness of breath

Chest x-rays of the lungs exhibit an opaque and glassy look against the black background

Worsening symptoms over the course of time, from the day of detection of the virus

While a vaccine for Covid 19 is still under work and might take a while before it is tested and certified for usage, our best bet right now is to stay safe, stay indoors and avoid crowds. A few simple precautions like maintaining hygiene and sanitizing your environment will go a long way in countering the spread of Covid 19 infection.