What the Flu Does to Your Body, and Why It Makes You Feel So Awful
By Laura Haynes
Every year, from 5 to 20 percent of the people in the U.S. will become infected with the influenza virus. An average of 200,000 of these people will require hospitalization and up to 50,000 will die. Older folks over the age of 65 are especially susceptible to influenza infection, since the immune system becomes weaker with age. In addition, older folks are also more susceptible to long-term disability following influenza infection, especially if they are hospitalized.
We all know the symptoms of influenza infection include fever, cough, sore throat, muscle aches, headaches and fatigue. But just what causes all the havoc? What is going on in your body as you fight the flu?
I am a researcher who specializes in immunology at the University of Connecticut School of Medicine, and my laboratory focuses on how influenza infection affects the body and how our bodies combat the virus. It's interesting to note that many of the body's defenses that attack the virus also cause many of the symptoms associated with the flu.
How the Flu Works Its Way Into Your Body
Influenza virus causes an infection in the respiratory tract, or nose, throat and lungs. The virus is inhaled or transmitted, usually via your fingers, to the mucous membranes of the mouth, nose or eyes. It then travels down the respiratory tract and binds to epithelial cells lining the lung airways via specific molecules on the cell surface. Once inside the cells, the virus hijacks the protein manufacturing machinery of the cell to generate its own viral proteins and create more viral particles. Once mature viral particles are produced, they are released from the cell and can then go on to invade adjacent cells.
Influenza gets a foothold in the respiratory tract but can make a person feel bad all over. Africa Studio / Shutterstock.com
While this process causes some lung injury, most of the symptoms of the flu are actually caused by the immune response to the virus. The initial immune response involves cells of the body's innate immune system, such as macrophages and neutrophils. These cells express receptors that are able to sense the presence of the virus. They then sound the alarm by producing small hormone-like molecules called cytokines and chemokines. These alert the body that an infection has been established.
Cytokines orchestrate other components of the immune system to appropriately fight the invading virus, while chemokines direct these components to the location of infection. One of the types of cells called into action are T lymphocytes, a type of white blood cell that fights infection. Sometimes, they are even called "soldier" cells. When T cells specifically recognize influenza virus proteins, they then begin to proliferate in the lymph nodes around the lungs and throat. This causes swelling and pain in these lymph nodes.
After a few days, these T cells move to the lungs and begin to kill the virus-infected cells. This process creates a great deal of lung damage similar to bronchitis, which can worsen existing lung disease and make breathing difficult. In addition, the buildup of mucous in the lungs, as a result of this immune response to infection, induces coughing as a reflex to try to clear the airways. Normally, this damage triggered by arrival of T cells in the lungs is reversible in a healthy person, but when it advances, it is bad news and can lead to death.
The proper functioning of influenza-specific T cells is critical for efficient clearance of the virus from the lungs. When T cell function declines, such as with increasing age or during use of immunosuppressive drugs, viral clearance is delayed. This results in a prolonged infection and greater lung damage. This can also set the stage for complications including secondary bacterial pneumonia, which can often be deadly.
Why Your Head Hurts So Much
While the influenza virus is wholly contained in the lungs under normal circumstances, several symptoms of influenza are systemic, including fever, headache, fatigue and muscle aches. In order to properly combat influenza infection, the cytokines and chemokines produced by the innate immune cells in the lungs become systemic—that is, they enter the bloodstream, and contribute to these systemic symptoms. When this happens, a cascade of complicating biological events occur.
One of the things that happens is that Interleukin-1, an inflammatory type of cytokine, is activated. Interleukin-1 is important for developing the killer T cell response against the virus, but it also affects the part of the brain in the hypothalamus that regulates body temperature, resulting in fever and headaches.
Another important cytokine that fights influenza infection is something called "tumor necrosis factor alpha." This cytokine can have direct antiviral effects in the lungs, and that's good. But it can also cause fever and appetite loss, fatigue and weakness during influenza and other types of infection.
Why Your Muscles Ache
Our research has also uncovered another aspect of how influenza infection affects our bodies.
It is well-known that muscle aches and weakness are prominent symptoms of influenza infection. Our study in an animal model found that influenza infection leads to an increase in the expression of muscle-degrading genes and a decrease in expression of muscle-building genes in skeletal muscles in the legs.
Functionally, influenza infection also hinders walking and leg strength. Importantly, in young individuals, these effects are transient and return to normal once the infection was cleared.
In contrast, these effects can linger significantly longer in older individuals. This is important, since a decrease in leg stability and strength could result in older folks being more prone to falls during recovery from influenza infection. It could also result in long-term disability and lead to the need for a cane or walker, limiting mobility and independence.
Researchers in my lab think that this impact of influenza infection on muscles is another unintended consequence of the immune response to the virus. We are currently working to determine what specific factors produced during the immune response are responsible for this and if we can find a way to prevent it.
Thus, while you feel miserable when you have an influenza infection, you can rest assured that it is because your body is fighting hard. It's combating the spread of the virus in your lungs and killing infected cells.
Reposted with permission from our media associate The Conversation.
By Pamela Davis-Kean
With in-person instruction becoming the exception rather than the norm, 54% of parents with school-age children expressed concern that their children could fall behind academically, according to a poll conducted over the summer of 2020. Initial projections from the Northwest Evaluation Association, which conducts research and creates commonly used standardized tests, suggest that these fears are well-grounded, especially for children from low-income families.
- How Other Countries Reopened Schools During the Pandemic ... ›
- Young People Are Primary Coronavirus Spreaders, WHO Warns ... ›
- How Families Can Boost Kids' Mental Health During the Pandemic ... ›
EcoWatch Daily Newsletter
The pandemic has affected everyone, but mental health experts warn that youth and teens are suffering disproportionately and that depression and suicide rates are increasing.
- How Families Can Boost Kids' Mental Health During the Pandemic ... ›
- How to Deal With Cabin Fever - EcoWatch ›
- 'Quarantine Fatigue' Is Real. Here's How to Cope - EcoWatch ›
Yet another former Trump administration staffer has come out with an endorsement for former Vice President Joe Biden, this time in response to President Donald Trump's handling of the coronavirus pandemic.
- Trump Denies CDC Director's 2021 Timeline for Coronavirus Vaccine ›
- Trump Orders Hospitals to Stop Sending COVID-19 Data to CDC ... ›
- Two White House Staffers Test Positive for Coronavirus - EcoWatch ›
- Trump Admin to Disband Coronavirus Task Force - EcoWatch ›
- Pence Offers 'Prayers' as Hurricane Laura Hits Gulf Coast While ›
Every September for the past 11 years, non-profit the Climate Group has hosted Climate Week NYC, a chance for business, government, activist and community leaders to come together and discuss solutions to the climate crisis.
- Covering the 2020 Elections as a Climate Story - EcoWatch ›
- Coronavirus Delays 2020 Earth Overshoot Day by Three Weeks ... ›
By Elliot Douglas
The coronavirus pandemic has altered economic priorities for governments around the world. But as wildfires tear up the west coast of the United States and Europe reels after one of its hottest summers on record, tackling climate change remains at the forefront of economic policy.
- German Business Leaders Call for Climate Action With COVID-19 ... ›
- Climate Activists Protest Germany's New Datteln 4 Coal Power Plant ... ›