COVID-19: How the coronavirus mounts a full body attack
Clinical reports and studies show that apart from the lungs the virus has the ability to infiltrate other parts of the body as well.
COVID-19, which has claimed over 191,000 lives across the world, is understood to primarily be a virus that attacks the lungs. However, clinical reports and studies from across the world are showing that this novel coronavirus has the ability to infiltrate other parts of the body as well. The vascular system, the gastrointestinal tract, the kidneys, the heart and even the neurological system seems to be affected.
A look at how it attacks the body can shed some light on what is going on.
The nose and throat: The infection begins in the nose and throat; in most cases, the person inhales droplets released by an infected person. The virus latches onto ACE-2 receptors in the upper nasal tract, invades cells and multiples. At this stage, the person is highly infectious but may not exhibit symptoms. In other cases, symptoms include fever, dry cough, sore throat, loss of smell and taste, or head and body aches.
In less severe cases, the immune system is able to mount a strong response and kill off the virus. In the more serious cases, the virus progresses to the lungs.
The lungs: The alveoli (air sacs in the lungs) are also rich in ACE-2 receptors. The virus latches onto these, and the immune response causes pus and debris to scatter across the lungs which makes breathing difficult. This causes the classical symptoms of pneumonia, including coughing, fever and shallow, rapid breathing. Some patients will fight off the infection here with little medical support, but others will develop Acute Respiratory Distress Syndrome (ARDS) wherein blood oxygen levels plummet and the body begins to get starved of oxygen. This can often be fatal, and ventilators may be required to keep the patient breathing.
What happens next?
This is where the picture gets complicated. An uncontrolled immune response called the cytokine storm could be triggered, and this could attack many vital organs. Some scientists believe that it is the cytokine storm that damages other body organs, and not the virus itself that attacks the organs. High levels of IL-6, a molecule associated with a hyperimmune response, have been registered in patients suffering from COVID-19.
The heart: A review from Chinese medical data showed that around 40% of severely ill patients suffered from arrhythmias (irregular heartbeats) and 20% had some form of cardiac injury. Doctors have also anecdotally reported that some patients that seem to be breathing normally, suddenly suffer cardiac trauma. ACE-2 receptors are present in our blood vessels as well, and many patients have presented with blood clotting disorders. This has led to symptoms such as swollen fingers and toes as blood circulation is affected and clots getting lodged in the lungs and brain, causing severe complications. Further, patients have also presented low blood oxygen levels along with regular breathing - this suggests that blood vessels may be directly under attack from the virus, and not a result of an immune reaction triggered by the lungs.
The gut: Around 20% of patients suffer gastric symptoms such as diarrhoea and vomiting. The GI tract also contains 100 times more ACE-2 receptors than other parts of the body. SARS, which was caused by another type of coronavirus, also attacked the GI system. Scans have shown damage to the colon, and over 50% of sampled patients’ faeces have shown evidence of the virus.
The kidneys, brain and liver: Studies have shown evidence of kidney damage; 59% of around 200 patients in Hubei and Sichuan had protein in their urine, and 44% had blood - all suggestive of suboptimal kidneys.
Similarly, with the liver, studies from China have shown that significant amounts of patients had elevated liver enzyme levels, which correlates with liver damage.
However, scientists say that ventilator support and certain drugs could also cause these effects, so there is uncertainty regarding kidney and liver damage.
A sizable subset of patients showed neurological symptoms such as confusion, strokes, seizures and brain inflammation. A study from Japan also showed evidence of the virus in cerebrospinal fluid.
More data needed
While there is growing evidence that the virus may directly attack organs other than the lungs, cytokine storms, the effects of drugs, respiratory distress and high fever may also explain the widespread symptoms. Time will give us more clarity, but the devastating effects of the virus are not to be doubted.
For more information, read our article on Complications of severe cases of COVID-19.
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