What does the coronavirus do in my body?
In this course, you will learn what the novel coronavirus does in your body, how it causes the COVID-19 illness and how your body fights back.
Let's learn with Jackie. Jackie went shopping last week with her friend Abby. Now Jackie is sick. It turns out that Abby had an infection with a virus called SARS-CoV-2 but didn’t know it.
SARS-CoV-2, known as the 2019 coronavirus, causes the sickness COVID-19. There are 7 types of coronaviruses known to infect humans; 4 cause a common cold while 3 cause worse infections.
Coronaviruses are named after the protein spikes that extend from their surface. These spikes form a sort of “corona” or “crown”. The spikes poke out of a layer of fat.
At the center of the virus is its genetic material, called RNA. This is the virus’ recipe for making new viruses. But to make this recipe, the virus needs to get into a living cell of your body.
SARS-CoV-2 can enter the body through the nose, eyes or mouth. Abby had coughed near Jackie when they went shopping. Jackie likely breathed the virus in through her nose or mouth.
SARS-CoV-2 bumps along through mucus passages in the nose and airways. It bumps along until it meets a cell with a protein called ACE2 on its surface. The virus’ spikes stick to ACE2.
ACE2 proteins sit on the surface of many cells in your body. But lots of ACE2 proteins cover the surface of your lung cells and some gut cells.
Once the virus’ spikes stick onto the ACE2, the virus can pass into the cell. Once it gets inside, its goal is to make copies of itself. The virus sneakily passes its RNA recipe to the cell’s recipe-making machinery.
In just one day inside Jackie’s body, a virus can trick her cells into making millions of virus copies. New viruses move to nearby cells, get inside and build more new viruses.
Jackie doesn't know she has COVID-19 until a few days after shopping with Abby. During this "incubation period" Jackie has no symptoms.
Avoid crowds and keep a distance from others to avoid catching the virus from someone who has it with no symptoms.
Scientists think that SARS-CoV-2 might be able to infect cells in both the upper and lower airways.
Some people show mild to no symptoms when infected, while others get sick.
The virus infects cells in Jackie’s upper airways. She has chills and a cough. She can’t really smell her food. She can easily spread virus particles to others when she coughs.
If the virus travels down and infects cells in Jackie’s lower airways, she could develop pneumonia or acute respiratory distress syndrome. This would make it hard for her to breathe.
- SARS-CoV-2 is an RNA virus. It needs to be inside living cells to make copies.
- You can get a coronavirus infection when others cough and sneeze near you. You might also bring virus into your body by touching your eyes, nose or mouth before washing your hands.
- The virus affects your airways.
Luckily, Jackie has an “army” in her body that fights off infection, called her immune system. In this army there are spies and patrols, messengers and soldiers.
Jackie has a young and strong immune army. Yet she could be sick for up to 2 weeks.
The virus' RNA contains a recipe for proteins that help the virus hide from her immune army.
But when there are many viruses and infected cells in Jackie’s airways, her immune army catches on. It sees an infection happening and it starts to act.
Jackie is young, so her immune army acts swiftly and efficiently once it finds the infection.
Continue to learn more about how your immune system fights viruses.
Within cells, there are special proteins that act as spies for your immune system. They go around, take samples of other proteins inside the cell, and then present them on the cell's surface.
Patrols called T cells check whether proteins on the surface of cells look normal or suspicious. While a virus can hide inside a cell, the spies present samples of the virus’ proteins on the cell’s surface.
When the T cells find evidence of a virus, they can send a "self-destruct" order into the infected cell. They alert the rest of the immune army using special messengers called cytokines.
The messengers bring in “soldier” immune cells. The soldiers come in as troops, ready to destroy infected cells to stop the virus from making more of itself.
But the messenger cytokines also create a bit of a mess, especially if too many of them signal too aggressively. They can cause inflammation in Jackie’s lungs.
As immune cells and dead lung cells and fluid collect in Jackie’s lungs, she might struggle to catch her breath. If this happens, she needs to call the emergency department.
But even while Jackie is sick, inside her body special immune cells are making antibodies. These important proteins mark viruses for destruction and block them from infecting healthy cells.
The battle favors Jackie’s strong immune army. Within a few days, her fever goes away and her cough gets better. Her lungs heal, creating new cells to replace damaged and dead ones.
But some people don’t have healthy immune armies. Their immune cells may be aged and tired, or distracted and preoccupied fighting other battles in the body.
Jackie’s uncle George is a man in his 70s with heart disease. He has also developed COVID-19. But it is more dangerous for him than it is for younger people like Jackie.
The aging immune system does not defend us from infection as well as it did when we were young. It also creates a lot of inflammation.
Inflammation contributes to chronic diseases like diabetes, heart disease, strokes and dementia.
George’s immune army is not very good at clearing the coronaviruses from his body. And when his army does respond to the virus, it not only reacts, it overreacts.
When George’s army overreacts, it causes a dangerous amount of inflammation and cell damage. As fluid builds up in his lungs, George becomes short of breath very easily. His wife calls the hospital. His chest feels heavy.
Lung cells usually pass oxygen into your bloodstream. When inflammation and damage builds up in the lungs, it gets in the way of oxygen trying to pass through.
If the body doesn’t get the oxygen it needs, the situation can become life-threatening. Lung damage and fluid buildup can lead to acute respiratory distress syndrome, or ARDS.
If George ends up having ARDS, the doctors may need to put him on a ventilator. It helps push oxygen into the lungs. It may be mechanical, where a tube goes into the body, or it may use a mask.
ARDS is very serious and can be life-threatening. However, people can recover. It may take time for them to get back to their normal strength.
Young people can have severe COVID illness, too. They are more at risk if their immune army is preoccupied by chronic disease like diabetes, or is suppressed from medication.
Keep your immune army strong and ready to fight viruses by eating a healthy diet including lots of fruits and vegetables. Get enough sleep, exercise, manage your stress and avoid cigarettes.
If you do get sick, your body can create antibodies that help destroy the virus before it enters your cells in the future.
People who are at higher risk of severe illness should try to stay home and away from people who could be sick.
What did you think of this course?
Dr. Calabrese is a Professor of Medicine and Vice Chair of the Cleveland Clinic’s Department of Rheumatic and Immunologic Diseases. He is interested in vascular inflammatory disease of the central nervous system, immunodeficiency and the intersection of infections and autoimmunity.
Dr. Belchamber is an immunologist from the UK, studying how immune cells work in the lungs. She loves taking pictures of cells under the microscope and helping people understand how their bodies work.
Haugs is a senior researcher at Center of Molecular Inflammation Research, Norwegian University of Science and Technology. He studies T-cell responses in HIV and mycobacterial infections.
Meås is a postdoc at Center of Molecular Inflammation Research, Norwegian University of Science and Technology. He studies innate and adaptive immune responses to HIV.
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