Every flu season, Americans battle coughs, fevers and body aches. The flu is a respiratory illness caused by a virus, a pathogen that causes disease in the human body. To understand how the flu is caught, spread and treated, Duke University's Katia Koelle explains the biology of a virus and how it is transmitted. "Science Behind the News" is produced in partnership with the National Science Foundation.
Science Behind the News - Influenza and Flu Vaccines
BRIAN WILLIAMS (FILE FOOTAGE):
Now we turn to health news about this year's flu season.
ANNE THOMPSON, reporting: It's flu season, the time of year when Americans are battling harsh coughs, high fevers, and intense body aches. According to the Centers for Disease Control and Prevention, as many as one in five Americans catch the flu each season, which occurs every winter from about October to March. While most years are mild, during the worst outbreaks the flu has the potential to become a global pandemic, killing thousands or even millions of people around the world as it did in 1918 during the so-called Spanish flu.
Dr. KATIA KOELLE (Duke University): It's an infectious disease so you can get it and you can spread it.
THOMPSON: Dr. Katia Koelle, an NSF-funded assistant professor of biology at Duke University, says the flu is a respiratory illness caused by a virus, the smallest and simplest of the pathogens that cause disease in the human body.
KOELLE: We have three different types of flu, influenza A, B, and C that are circulating in humans. So the flu virus is actually kind of a set of viruses.
THOMPSON: What distinguishes viruses from other pathogens - bacteria, fungi and protozoa - is that viruses require a living host, such as a human, to help them reproduce.
KOELLE: They can't survive on their own. They really need the machinery of hosts to replicate and spread.
THOMPSON: The influenza virus spreads from person to person through droplets of moisture that are released when an infected person coughs, sneezes or talks. As these droplets enter the body, the virus attaches itself to an epithelial cell, the type of cells that line the respiratory track.
KOELLE: The virus then can actually gain entry into your epithelial cells and it does so by using a certain protein that's on the viral surface.
THOMPSON: This is the first step in the viral reproduction process called the lytic cycle. As the virus enters the healthy host cell, it takes over all metabolic functions by inserting its RNA, replicating itself, and eventually destroying the host cell and spreading the virus to other healthy cells in the respiratory tract.
KOELLE: Once you actually get exposed to the virus, usually it takes a day or two for you to start showing symptoms. And then you have symptoms for three to five days.
THOMPSON: Beyond frequent hand washing with soap, the best way to prevent the flu is to get a vaccination a few weeks before the flu season begins in October. Flu researchers at the World Health Organization create a vaccine from dead viruses from several strains of the most prevalent forms of the flu thought to be circulating the world. A new vaccine is needed each year in order to keep up with the rapidly evolving family of flu viruses. The vaccine can't hurt you and you can't catch the flu from it, but it does trigger an immune response.
KOELLE: If you get a vaccine, what happens is that that vaccine generates your immune response and so your body is kind of tricked into seeing this vaccine and thinking it's flu.
THOMPSON: After getting vaccinated, your immune system builds up antibodies to defend against the virus if it enters your system. If you do become infected with the flu, there are antiviral drugs available, like Tamiflu, which bond to the flu virus's protein shell preventing it from spreading from cell to cell.
KOELLE: What antivirals do is they usually shorten the period of time that you're actually infectious. So that's also good because if you shorten that period, it's good for you and it's also good in terms of decreasing the chance that you're going to transmit it to someone else.
THOMPSON: While there is no cure, understanding what the flu virus is and how it's transmitted can help lessen the impact of the annual flu season.
WASHINGTON, D.C. — The descriptions are haunting.
Some victims felt fine in the morning and were dead by night. Faces turned blue as patients coughed up blood. Stacked bodies outnumbered coffins.
A century after one of history's most catastrophic disease outbreaks, scientists are rethinking how to guard against another super-flu like the 1918 influenza that killed tens of millions as it swept the globe.
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