How the virus affect younger, seemingly healthy individuals

Researchers are still working out how the virus acts at this point in time.

"There are early days when it comes to how the COVID-19 virus communicates with the body and how it causes symptoms and sometimes kills people," says Vikram Misra, professor at the University of Saskatchewan's department of microbiology in Saskatoon.

Here are a few things we do know. The novel virus is part of a family of viruses called coronaviruses. Named for their telltale crown-like spikes, they mainly infect bats, pigs, and small mammals, but can migrate from animals to humans and from one human to another.

Many pathogens can infect humans, including two that have proved extremely deadly: SARS (Severe Acute Respiratory Syndrome) and MERS, or Respiratory Syndrome in the Middle East.

When COVID-19 enters the body — through droplets in the air — it appears to be bound to a particular lung tissue receptor. From there, it “hijacks” the host cell’s mechanisms to make more copies of itself. Tissue damage happens as a result of viruses taking over the cell completely, causing it to die, or when immune cells mount a defense against the viral infection, leading to cell death.

If huge numbers of cells die, then the affected organ, in this case, the lung can’t function effectively.

“Typically, coronavirus causes respiratory infections,” says Matthew S. Miller, associate professor at Michael G. De Groote Institute for Study on Infectious Diseases at the McMaster Immunology Research Centre, McMaster University. Modern coronaviruses infecting humans every year typically cause moderate, uncomplicated upper respiratory infection.

“The different and unique about the virus that’s causing this outbreak is that it can cause acute respiratory distress,” says the head of the university’s Miller Laboratory. “That means that the patient’s lungs can accumulate fluid, for example, which is more typical of pneumonias. It’s the respiratory failure or cardio-respiratory issues that lead to patients dying.”

Those with serious COVID-19 cases undergo a clinical syndrome, known as a "cytokine storm," says Miller. The term describes an overproduction of immune cells (cytokines) and their activating compounds. A flood of activated immune cells comes into the lungs.

This essentially means too much of a good thing: The strength of the immune response can put a healthy person at risk for complications associated with respiratory illness.

“The immune system overacts with the infection, and it's the immune system that causes lung damage rather than the virus itself, "says Miller. “Cytokine a storm is also consistent with the disease that SARS caused and is also consistent with what we sometimes see in people who are severely ill with influenza virus infection.

“An immune system the analogy might be: Instead of using a fly swatter to squash a fly you use a sledgehammer and punch a hole in the wall,” he says.

The lungs are highly vascularized, Miller explains: There’s a lot of blood flow in the lungs, because they’re the site of gas exchange. Normally, you want your airways to be relatively dry so that you can breathe in air, which gets transferred to red blood cells and carried to the rest of the body.

“During infections or immune responses, the tissue becomes damaged, then the fluid that’s normally contained in the blood vessels starts to leak into airways,” Miller says. “That build-up of fluid in the lungs are what can cause breathing distress because now lungs aren’t exchanging gas very efficiently.”

Cytokine storms can have other effects on the lungs, such as inflammation.

“You can have a lot of inflammation in your lungs' says Misra. “Inflammation is always a bad thing. With 1918 the influenza virus that killed millions of people, experiments done in the last 10 years show that inflammation was the killer in that case as well, because of the cytokine storm.”