Infection with the novel coronavirus can lead to coronavirus disease (Covid-19). This can cause mild to severe symptoms.

How Covid-19 goes from mild to deadly

Two new Chinese studies have outlined a step-by-step path for how the coronavirus goes from mild to deadly.

DURBAN – An infection with the novel coronavirus can lead to coronavirus disease (Covid-19). This can cause mild to severe symptoms. In some people, it leads to life-threatening complications.

Two new Chinese studies, one from researchers at Zunyi Medical University published in Frontiers in Public Health and another study out of Wuhan University have outlined a step-by-step path for how the coronavirus goes from mild to deadly:

 

  • Step One: The virus’ spiky proteins latch onto cell receptors found throughout the body called ACE2. It starts by binding to ACE2 receptors in the lungs.

 

  • Step Two: The immune system senses a threat and responds by activating white blood cells. Wuhan researchers found an “obvious increase” in two types of white blood cells — leukocytes and neutrophils — and a decrease in lymphocytes (another type of white blood cell) among critically ill patients. 

 

  • Step Three: White blood cells release too many cytokines: proteins that further activate the immune response and trigger inflammation in the body. 

 

  • Step Four: This “cytokine storm” prompts white blood cells to attack healthy lung tissue. The reaction can lead to severe symptoms including blood clots, excessive leaking in the blood vessels, fluid in the lungs, depleted oxygen in the blood, and low blood pressure. 

 

  • Step Five: An aggressive immune response can damage the lungs, heart, kidneys, intestines, and liver. Wuhan researchers found elevated levels of two proteins that may signal a heart attack — highly sensitive troponin I and C-reactive proteins — among severe and critically ill patients. 

 

  • Step Six: Proteins and dead cells form a membrane around the alveoli (tiny air sacs in the lungs) making it difficult to absorb oxygen. This can lead to acute respiratory distress syndrome (ARDS), a life-threatening lung injury. 

 

  • Step Seven: Most coronavirus deaths are due to respiratory failure, but many patients also experience multiple organ failure. Out of 18 patients who died in the study, 17 developed ARDS, 10 suffered from an acute cardiac injury, and 7 suffered from acute kidney injury. All but one patient presented signs of a secondary bacterial infection on the day of death. 

 

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