Someone coughs, you breath it in. Or, someone touches a surface with unclean hands, you touch the surface, then you touch an opening into your body, like your nose or mouth or eye.
coronavirus in your cell
The coronavirus is able to gain entry into cells by using the protein ACE-2 as a receptor that then unlocks the cell to the invading virus. Once inside, the virus uses your own cell to reproduce, eventually busting out of the cell and spreading.
It first infects the cells lining your throat, airways and lungs. Still, you might have no symptoms, even though the virus is cranking out replicas of itself, getting a head start on the immune system.
days ’til symptoms start (or “incubation period”)
Data is still being analyzed, but here’s what is being reported by the WHO:
1-14 days (time from when you are infected to when you are sick), with an average of 5-6 days. Up to a 24-day incubation period has been reported.
how contagious, or R0 (pronounced “R-NOT”)
So far, an R0 value of 2-3 has been calculated: in other words, each person with the virus is likely to infect 2-3 other people.
Most people will get a fever (83% to 98%) and a dry cough (76% to 82%). Some may be tired and achy (11-44%).
Headache, sore throat, abdominal pain, and diarrhea have also been reported.
normal lung function
Normally, you breath in oxygen, and this oxygen moves into the tiny sacs in the lung called alveoli. Blood moving past the alveoli takes up the oxygen and delivers it to the the rest of the body.
lungs with pneumonia
If you have pneumonia, areas of your lung may be inflamed. In the areas that are inflamed, fluid builds up (this is the immune response to the infection). This fluid gets in the way of moving oxygen into the bloodstream.
The coronavirus can result in pneumonia.
lungs with acute respiratory distress syndrome (ARDS)
ARDS is when the entire lung is inflamed, and fluid builds up, getting in the way of oxygen getting into the bloodstream. Also, liquid from blood begins to leak into the alveoli which–because they’re fluid-filled–means the lungs are even less able to move oxygen into the blood.
If oxygen can’t get into the blood, the rest of the body doesn’t get what it needs to function, which can lead to organ failure.
Ventilators are used to push oxygen into lungs until swelling goes away.
worse, an immune overkill can happen
Whether a coronavirus infection gets even worse depends on a person’s immune response.
When the coronavirus is attacking cells in the respiratory tract (throat, lungs, etc) the immune system kicks in, and inflammation results from a flood of white blood cells sent to eradicate the virus. White blood cells eventually take over the pathogen, the immune response slows, you recover. All is good.
In some people, the immune response is over-the-top, though.
In some people, immune cells and their signaling molecules (it’s a very complex system) are overproduced, which leads to a “cytokine storm.”
Cytokines are a group of proteins that signal and communicate the immune response (it’s super complicated). When the immune system is fighting something like coronavirus, cytokines send immune-response cells to the infection–in this case, the lungs. Cytokines also activate cells to produce more cytokines, which allows more signals to respond to infection. Normally, this is kept regulated by the body.
Sometimes, this signaling becomes uncontrolled, though, and too many immune cells are activated–maybe because the pathogen is new and highly aggressive–we don’t really know why this over-response can happen. This “cytokine storm” causes inflammation that then results in the most severe symptoms of the coronavirus disease: pneumonia, difficulty breathing, and organ damage.
NOTE: An incorrect hypothesis was circulating on social media that unhealthy immune systems are better than healthy immune systems at avoiding a cytokine response, presumably because an unhealthy immune system would under-react rather than over-react to coronavirus. First, the cytokine storm is a low risk for the majority of infected patients, and prognosis is better with a healthy immune system. Secondly, this cytokine response is a highly complicated system of feedback loops, alternate pathways, and interactions that–due to their complexity–are not even completely understood. It’s overly simplistic (and inaccurate) to hope for an underperforming immune system to increase your chances at battling the coronavirus.
Cytokine storms can result from various infections but they often come after exposure to certain strains of flu. For example, researchers believe that cytokine storms caused many of the deaths associated with the Spanish Flu of 1918-1920 and the more recent outbreaks of bird flu and swine flu.