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 Dana M Bergstrom, Euan Ritchie, Lesley Hughes and Michael Depledge
In 1992, 1,700 scientists warned that human beings and the natural world were "on a collision course." Seventeen years later, scientists described planetary boundaries within which humans and other life could have a "safe space to operate." These are environmental thresholds, such as the amount of carbon dioxide in the atmosphere and changes in land use.
The Good and Bad News<p><span>Ecosystems consist of living and non-living components, and their interactions. They work like a super-complex engine: when some components are removed or stop working, knock-on consequences can lead to system failure.</span></p><p>Our study is based on measured data and observations, not modeling or predictions for the future. Encouragingly, not all ecosystems we examined have collapsed across their entire range. We still have, for instance, some intact reefs on the Great Barrier Reef, especially in deeper waters. And northern Australia has some of the most intact and least-modified stretches of savanna woodlands on Earth.</p><p><span>Still, collapses are happening, including in regions critical for growing food. This includes the </span><a href="https://www.mdba.gov.au/importance-murray-darling-basin/where-basin" target="_blank" rel="noopener noreferrer">Murray-Darling Basin</a><span>, which covers around 14% of Australia's landmass. Its rivers and other freshwater systems support more than </span><a href="https://www.abs.gov.au/ausstats/[email protected]/latestproducts/94F2007584736094CA2574A50014B1B6?opendocument" target="_blank" rel="noopener noreferrer">30% of Australia's food</a><span> production.</span></p><p><span></span><span>The effects of floods, fires, heatwaves and storms do not stop at farm gates; they're felt equally in agricultural areas and natural ecosystems. We shouldn't forget how towns ran out of </span><a href="https://www.mdba.gov.au/issues-murray-darling-basin/drought#effects" target="_blank" rel="noopener noreferrer">drinking water</a><span> during the recent drought.</span></p><p><span></span><span>Drinking water is also at risk when ecosystems collapse in our water catchments. In Victoria, for example, the degradation of giant </span><a href="https://theconversation.com/logging-must-stop-in-melbournes-biggest-water-supply-catchment-106922" target="_blank" rel="noopener noreferrer">Mountain Ash forests</a><span> greatly reduces the amount of water flowing through the Thompson catchment, threatening nearly five million people's drinking water in Melbourne.</span></p><p>This is a dire <em data-redactor-tag="em">wake-up</em> call — not just a <em data-redactor-tag="em">warning</em>. Put bluntly, current changes across the continent, and their potential outcomes, pose an existential threat to our survival, and other life we share environments with.</p><p><span>In investigating patterns of collapse, we found most ecosystems experience multiple, concurrent pressures from both global climate change and regional human impacts (such as land clearing). Pressures are often </span><a href="https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2664.13427" target="_blank" rel="noopener noreferrer">additive and extreme</a><span>.</span></p><p>Take the last 11 years in Western Australia as an example.</p><p>In the summer of 2010 and 2011, a <a href="https://theconversation.com/marine-heatwaves-are-getting-hotter-lasting-longer-and-doing-more-damage-95637" target="_blank" rel="noopener noreferrer">heatwave</a> spanning more than 300,000 square kilometers ravaged both marine and land ecosystems. The extreme heat devastated forests and woodlands, kelp forests, seagrass meadows and coral reefs. This catastrophe was followed by two cyclones.</p><p>A record-breaking, marine heatwave in late 2019 dealt a further blow. And another marine heatwave is predicted for <a href="https://www.theguardian.com/environment/2020/dec/24/wa-coastline-facing-marine-heatwave-in-early-2021-csiro-predicts" target="_blank" rel="noopener noreferrer">this April</a>.</p>
What to Do About It?<p><span>Our brains trust comprises 38 experts from 21 universities, CSIRO and the federal Department of Agriculture Water and Environment. Beyond quantifying and reporting more doom and gloom, we asked the question: what can be done?</span></p><p>We devised a simple but tractable scheme called the 3As:</p><ul><li>Awareness of what is important</li><li>Anticipation of what is coming down the line</li><li>Action to stop the pressures or deal with impacts.</li></ul><p>In our paper, we identify positive actions to help protect or restore ecosystems. Many are already happening. In some cases, ecosystems might be better left to recover by themselves, such as coral after a cyclone.</p><p>In other cases, active human intervention will be required – for example, placing artificial nesting boxes for Carnaby's black cockatoos in areas where old trees have been <a href="https://www.environment.gov.au/biodiversity/threatened/publications/factsheet-carnabys-black-cockatoo-calyptorhynchus-latirostris" target="_blank" rel="noopener noreferrer">removed</a>.</p><p><span>"Future-ready" actions are also vital. This includes reinstating </span><a href="https://www.abc.net.au/gardening/factsheets/a-burning-question-fire/12395700" target="_blank" rel="noopener noreferrer">cultural burning practices</a><span>, which have </span><a href="https://theconversation.com/australia-you-have-unfinished-business-its-time-to-let-our-fire-people-care-for-this-land-135196" target="_blank" rel="noopener noreferrer">multiple values and benefits for Aboriginal communities</a><span> and can help minimize the risk and strength of bushfires.</span></p><p>It might also include replanting banks along the Murray River with species better suited to <a href="https://www.abc.net.au/gardening/factsheets/my-garden-path---matt-hansen/12322978" target="_blank" rel="noopener noreferrer">warmer conditions</a>.</p><p>Some actions may be small and localized, but have substantial positive benefits.</p><p>For example, billions of migrating Bogong moths, the main summer food for critically endangered mountain pygmy possums, have not arrived in their typical numbers in Australian alpine regions in recent years. This was further exacerbated by the <a href="https://theconversation.com/six-million-hectares-of-threatened-species-habitat-up-in-smoke-129438" target="_blank" rel="noopener noreferrer">2019-20</a> fires. Brilliantly, <a href="https://www.zoo.org.au/" target="_blank" rel="noopener noreferrer">Zoos Victoria</a> anticipated this pressure and developed supplementary food — <a href="https://theconversation.com/looks-like-an-anzac-biscuit-tastes-like-a-protein-bar-bogong-bikkies-help-mountain-pygmy-possums-after-fire-131045" target="_blank" rel="noopener noreferrer">Bogong bikkies</a>.</p><p><span>Other more challenging, global or large-scale actions must address the </span><a href="https://www.youtube.com/watch?v=iICpI9H0GkU&t=34s" target="_blank" rel="noopener noreferrer">root cause of environmental threats</a><span>, such as </span><a href="https://www.nature.com/articles/s41559-018-0504-8" target="_blank" rel="noopener noreferrer">human population growth and per-capita consumption</a><span> of environmental resources.</span><br></p><p>We must rapidly reduce greenhouse gas emissions to net-zero, remove or suppress invasive species such as <a href="https://onlinelibrary.wiley.com/doi/abs/10.1111/mam.12080" target="_blank" rel="noopener noreferrer">feral cats</a> and <a href="https://theconversation.com/the-buffel-kerfuffle-how-one-species-quietly-destroys-native-wildlife-and-cultural-sites-in-arid-australia-149456" target="_blank" rel="noopener noreferrer">buffel grass</a>, and stop widespread <a href="https://theconversation.com/to-reduce-fire-risk-and-meet-climate-targets-over-300-scientists-call-for-stronger-land-clearing-laws-113172" target="_blank" rel="noopener noreferrer">land clearing</a> and other forms of habitat destruction.</p>
Our Lives Depend On It<p>The multiple ecosystem collapses we have documented in Australia are a harbinger for <a href="https://www.iucn.org/news/protected-areas/202102/natures-future-our-future-world-speaks" target="_blank">environments globally</a>.</p><p>The simplicity of the 3As is to show people <em>can</em> do something positive, either at the local level of a landcare group, or at the level of government departments and conservation agencies.</p><p>Our lives and those of our <a href="https://theconversation.com/children-are-our-future-and-the-planets-heres-how-you-can-teach-them-to-take-care-of-it-113759" target="_blank">children</a>, as well as our <a href="https://theconversation.com/taking-care-of-business-the-private-sector-is-waking-up-to-natures-value-153786" target="_blank" rel="noopener noreferrer">economies</a>, societies and <a href="https://theconversation.com/to-address-the-ecological-crisis-aboriginal-peoples-must-be-restored-as-custodians-of-country-108594" target="_blank" rel="noopener noreferrer">cultures</a>, depend on it.</p><p>We simply cannot afford any further delay.</p><p><em><a rel="noopener noreferrer" href="https://theconversation.com/profiles/dana-m-bergstrom-1008495" target="_blank" style="">Dana M Bergstrom</a> is a principal research scientist at the University of Wollongong. <a rel="noopener noreferrer" href="https://theconversation.com/profiles/euan-ritchie-735" target="_blank" style="">Euan Ritchie</a> is a professor in Wildlife Ecology and Conservation, Centre for Integrative Ecology, School of Life & Environmental Sciences at Deakin University. <a rel="noopener noreferrer" href="https://theconversation.com/profiles/lesley-hughes-5823" target="_blank">Lesley Hughes</a> is a professor at the Department of Biological Sciences at Macquarie University. <a rel="noopener noreferrer" href="https://theconversation.com/profiles/michael-depledge-114659" target="_blank">Michael Depledge</a> is a professor and chair, Environment and Human Health, at the University of Exeter. </em></p><p><em>Disclosure statements: Dana Bergstrom works for the Australian Antarctic Division and is a Visiting Fellow at the University of Wollongong. Her research including fieldwork on Macquarie Island and in Antarctica was supported by the Australian Antarctic Division.</em></p><p><em>Euan Ritchie receives funding from the Australian Research Council, The Australia and Pacific Science Foundation, Australian Geographic, Parks Victoria, Department of Environment, Land, Water and Planning, and the Bushfire and Natural Hazards CRC. Euan Ritchie is a Director (Media Working Group) of the Ecological Society of Australia, and a member of the Australian Mammal Society.</em></p><p><em>Lesley Hughes receives funding from the Australian Research Council. She is a Councillor with the Climate Council of Australia, a member of the Wentworth Group of Concerned Scientists and a Director of WWF-Australia.</em></p><p><em>Michael Depledge does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</em></p><p><em>Reposted with permission from <a href="https://theconversation.com/existential-threat-to-our-survival-see-the-19-australian-ecosystems-already-collapsing-154077" target="_blank" style="">The Conversation</a>. </em></p>
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