Welcome to Epidemics, an online course about the dynamics of infectious diseases. We have so many exciting things to share with you. >>We're going to take you on a tour through this important field that touches every aspect of our daily lives. And we have assembled a group of world class scientists. All working at the Centre for Infectious Disease Dynamics, here at Penn State. >> Infectious diseases have always been a major killer throughout human history. Most of the time they are a part of the everyday struggle to survive, causing both illness and death. Though, periodically, a single disease would rip through a population in an epidemic, killing huge numbers of people in a short period of time. For example, in the Middle Ages, an epidemic of bubonic plague or Black Death caused by the bacterium Yersinia pestis, spread across Europe, and within just four years is estimated to have killed three in ten Europeans. Though there are many diseases that are always present in populations, the term epidemic describes those diseases caused by infectious microorganisms that occasionally occur in large numbers. Once introduced into a population, infectious microorganisms such as viruses and bacteria. Can spread from person to person. And so long as each person transmits the infection to more than other person, the number of cases of disease will grow and grow exponentially leading to the dramatic spread that characterizes an epidemic. >>The term infectious disease is actually a bit of a misnomer. It is not the disease that is spreading. But rather, the organisms that cause the disease. The term is here to stay, of course. And it's a good reminder that there are diseases whose underlying cause cannot spread from person to person. For example, diseases that have genetic causes, or diseases that are due to toxins in the environment. But, even diseases that most people wouldn't think of as infectious diseases can be caused by transmissible microorganisms.For example, most people are surprised to learn that about 20% of all cancers are caused by viruses and bacteria. Moreover, not every infection always causes disease. Disease when caused by microorganisms is always an outcome of an intricate interplay between the biology of the microorganism, the biology of the host, and the environment. For example, Matt and I could be exposed to the exact same virus, yet one of us might develop a disease with all its symptoms while the other one will stay perfectly healthy. >> Nowadays, because of improved sanitation and medical treatment, infectious diseases don't pose the same kind of everyday threat that they used to. At the beginning of the last century in the United States, infectious disease caused 800 deaths per 100,000 people every year. Clearly, modern advancements have drastically reduced the likelihood of death due to infectious causes. Though, individual epidemics, such as the 1918 influenza pandemic, are stark reminders of the potential consequences of infectious disease. >> But make no mistake, left unchecked; microorganisms would kill us by the millions. The reason we have some aspects of this problem under control. Is because of science and because of our understanding about how microorganisms spread, cause disease, and how our bodies fight back. And this is what you will learn in this course. The struggle to control infectious diseases is a truly multidisciplinary fight. As an example, take a pandemic, which is a world-wide epidemic. When a pandemic of a newly-emerging disease unfolds, we need biologists to identify the underlying molecular mechanisms of infection. We need medical doctors to prevent and treat the disease. We need public health specialists to understand what kinds of strategies governments can put in place to curb the spread of the disease. We need communication experts to understand how to disseminate information thorough various media channels. And in this day and age, we'd want computational scientists to make use of the latest technological advances in mobile computing so that we can monitor the situation in real time. >> And once we have a disease under control, the fight is not over. The microorganisms that cause diseases are not static. They're biological organisms subject to their own struggle for existence. And, they are constantly changing in order to survive in the face of changes that we impose upon them. We see this struggle for existence in the development of resistance to the drugs and vaccines that we employ to prevent disease spread. For example, the rise of antibiotic resistance is a direct consequence of evolution in bacteria in response to the drugs that we use to treat them. >> The sobering truth is this. The fight against infectious disease will never cease to exist. As long as there's life, there will be infectious disease. Our species has done a pretty amazing job dealing with this problem. But we're not done, and we will never be. But unlike our ancestors who had to resort to superstition, black magic, and mythology, we can rely on science to understand what it is that makes us sick. How it spreads and how we can stop it. Our goal in this course is to share with you what science has uncovered about the spread of infectious diseases.