EMILY GURLEY: Hello, my name is Emily Gurley, and I'm an infectious disease epidemiologist at the Johns Hopkins Bloomberg School of Public Health. Today, I'm going to talk to you about the basics of COVID-19, including the virus that causes this disease, some of the signs and symptoms of the disease, and how it's transmitted between people. During this lecture, there are a number of important things we want you to learn. We want you to be able to describe the origins of the virus that causes the disease we call COVID-19. We want you to be able to identify the clinical signs and symptoms of COVID-19 and to be able to talk something about the risk factors for severe disease. You should be able to describe how someone is diagnosed with COVID-19 and describe when they're infectious. And importantly, you should also be able to explain how this virus is transmitted from one person to another, and how frequently that happens. Now let's talk about the virus that causes COVID-19. So the virus that causes COVID-19 is a coronavirus. Coronaviruses are a large, diverse group of viruses, and you need powerful microscopes to be able to see them. Coronavirus means crown. And as you can see on this slide, the virus looks like it has a crown around it. That's how coronaviruses got their name. There are many different types of coronaviruses, and they infect a wide range of mammals and birds. And some even cause mild respiratory disease in people every year, so coronaviruses are not new. But the virus that causes COVID-19 is, so let's talk a little bit about where that came from. The virus that causes COVID-19, we call SARS coronavirus two. This virus originated in bats, so that means that bats carry this virus and are infected with this virus all the time. But this virus developed a special trick. It developed the ability to jump between species and infect people. And then it developed another very special trick to be able to be transmitted between people, and that's how it came to cause the pandemic that we're experiencing now. So this kind of trick that some coronavirus viruses have also isn't new, so this is the third coronavirus that we know of since 2002 that has developed these same tricks. All of these coronaviruses also originated in bats now infect people and can be spread from person to person. So the first of these viruses was called severe acute respiratory syndrome, or SARS coronavirus, the first SARS coronavirus. And that emerged in Guangdong, China in 2002. The next virus to develop this trick was the Middle Eastern Respiratory Syndrome Coronavirus or MERS. That emerged in the Middle East in 2012 and still causes human infections and small outbreaks there. More recently at the end of 2019, SARS coronavirus two emerged in Wuhan, China. And because the virus is similar to the virus that caused the first SARS coronavirus, it was named SARS coronavirus two. Here, you can see in yellow some SARS coronaviruses coming out of a cell. Viruses have to live in other cells, and then they replicate in those cells and go on to infect other cells in the body.