How COVID-19 coronavirus attacks your body

How COVID-19 coronavirus attacks your body, by Sumathi Reddy.

It starts, most often, with a cough or a sneeze. Thousands of tiny, often invisible droplets of saliva or mucus disperse in the air. You walk by — within about 1.8m of the offender — and inadvertently inhale the droplets. …

The virus most commonly enters the nose through minuscule droplets from someone’s mucus or saliva … It can also enter through the eyes or mouth.

Once the virus’s particles enter the body, they begin to attach to a particular receptor on the surface of the body’s cells, usually starting with cells in the mucous membranes in the nose and throat. The coronavirus is distinguished by spiky proteins on its surface; these spikes latch onto cell membranes. The virus then enters the cells and disassembles so its RNA — molecules that carry instructions from DNA to the body’s cells — can start to reproduce. …

Though most people likely start with an upper respiratory infection, it’s also possible that respiratory droplets are inhaled more deeply and go directly into the lungs, says Brian Garibaldi, an associate professor of pulmonary and critical care at Johns Hopkins University. “It has a special protein that binds more tightly to cells in the lower respiratory tract,” he says.

Wherever it lands, the virus hijacks cells and starts replicating, ultimately producing millions of viral particles that flood the body. …

Once the virus has attacked enough cells in the upper respiratory system, most people will start to feel symptoms. This happens on average five days after being exposed to the virus but it can be sooner or as many as two weeks later, studies show.

These early symptoms usually include a dry cough and fever, and sometimes a sore throat, as well as aches and fatigue. Loss of taste and smell have also been reported as early signs of infection.

For the majority of people — roughly 80 per cent according to reports from China — the symptoms end there and dissipate in a few days or weeks.

But for some people, predominantly older people and those with other medical conditions, the virus keeps travelling down and invading cells in the lungs.

When the cells start moving down the respiratory system into the lungs it becomes a lower respiratory illness, which is considered more serious. That could happen two to seven days after symptoms start …

Once the virus starts infecting the cells that line the air sacs in the lungs, viral pneumonia develops, which is inflammation of the lungs. Shortness of breath is an indication that the virus is damaging the lungs. …

And the lungs often face a two-way assault. There is damage from the virus but a second equally debilitating response takes place: The body’s own immune system goes into overdrive, causing more lung damage. …

When the lung becomes progressively more damaged, that triggers what is known as acute respiratory distress syndrome, or ARDS. This typically develops seven to 14 days into the course of the illness.

The lungs become less efficient at exchanging oxygen and carbon dioxide and continue to become inflamed. Patients need assistance breathing because there’s no therapy to treat ARDS.

“The ventilator is buying time for the lung to repair itself after a virus has run its course and the immune system response has calmed down, ” Dr Garibaldi says.