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>> Hi, everyone. I'm Andy Carlson. I'm and infectious diseases doctor at the Centers for Disease Control and Prevention here in Atlanta, Georgia. We're continuing our infection control series, our Inside Infection Control video series, today, from Project Firstline, and we're going to talk more about viruses, specifically, how viruses make us sick. The things that we do for infection control for COVID-19 are all to keep the virus that causes COVID-19, SARS CoV-2, from getting into our eyes, nose, and mouth, or someone else's, where it can make us sick. But a question that you might have is, well, how does that happen? What does a virus do when it gets into the body to make us feel sick? Knowing a little more about how viruses work helps to understand the things that we do for infection control. We talked and another earlier episode about the parts of a virus. If you haven't seen that episode yet, please do go check it out when you're done here, but today, we're going to talk about how viruses are able to use cells in living things, including people, to make more copies of themselves, to spread within the body, and to move from person to person. So, our bodies have billions of cells. They are like microscopic building blocks. Or cells are very different from viruses, but they do have some things in common, and one of those things is that they have little parts made out of protein that stick out of the surface of the cell, just like a virus has proteins that stick out of the surface of the virus. And some of those little parts that stick on the outside of the cell, they work like a lock on a door. If you have a key to that lock, you can get into the cell. If you don't have the key, you can't get in, but viruses that can make us sick have found a way to make a false key, a little part that sticks out from the surface of the virus that will fit into a lock on at least one type of our cells. It's not an exact match, but it's close enough that the virus can hack in and invade that type of cell. It's not that our bodies meant for this to happen. The locks on our cells aren't for viruses. They're for things our bodies naturally and normally do, and viruses can't hack into every cell type, just the ones where their keys match the lock close enough. But when a virus can get inside, it hijacks the machinery of the cell and uses it to make more copies of itself, including more copies of that false key. Those new virus copies with their false keys on the outside, they then break out of those infected cells and move on to infect new cells, and in many cases, the cell that's been infected and hijacks is destroyed in the process. As the virus starts hacking into more and more of our cells, the body recognizes that, uh-oh, there's an infection. The body then sends out an alarm to rev up the immune system, so it can fight off the virus, and it's actually that activity of our immune system getting to work that makes us feel sick. That's where the fever, the chills, cough, and other symptoms come from. Now there are times when the immune system is fighting a virus, but a person doesn't feel sick. When this happens, that person can still spread virus, even though they don't know they're infected, and it's a big problem for infection control that we're going to talk about more and another video. So, what happens when you're infected with a respiratory virus, whether you know it or not, and you cough or breathe out or talk? Well, your droplets with virus in them are carried out, reaching other people, getting into their nose, mouth, throat, and lungs and infecting them, and this whole process in the cell that we just talked about starts all over again. But we don't want that to happen, and that's why as we talk about these things that we do for infection control, you'll see that many of them focus on keeping respiratory droplets out of the air and away from other people. As always, thanks for joining us. Please be sure to follow up with us on Facebook or Twitter, and check us out on the web at CDC.gov/ProjectFirstline. We'll see you back here for the next episode.