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What the Flu Does to Your Body, and Why It Makes You Feel So Awful

Health + Wellness

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.

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The huge surge this year in Amazon deforestation is leading some European countries to think twice about donations to the Amazon Fund. LeoFFreitas / Moment / Getty Images

By Sue Branford and Thais Borges

Ola Elvestrun, Norway's environment minister, announced Thursday that it is freezing its contributions to the Amazon Fund, and will no longer be transferring €300 million ($33.2 million) to Brazil. In a press release, the Norwegian embassy in Brazil stated:

Given the present circumstances, Norway does not have either the legal or the technical basis for making its annual contribution to the Amazon Fund.

Brazilian President Jair Bolsonaro reacted with sarcasm to Norway's decision, which had been widely expected. After an official event, he commented: "Isn't Norway the country that kills whales at the North Pole? Doesn't it also produce oil? It has no basis for telling us what to do. It should give the money to Angela Merkel [the German Chancellor] to reforest Germany."

According to its website, the Amazon Fund is a "REDD+ mechanism created to raise donations for non-reimbursable investments in efforts to prevent, monitor and combat deforestation, as well as to promote the preservation and sustainable use in the Brazilian Amazon." The bulk of funding comes from Norway and Germany.

The annual transfer of funds from developed world donors to the Amazon Fund depends on a report from the Fund's technical committee. This committee meets after the National Institute of Space Research, which gathers official Amazon deforestation data, publishes its annual report with the definitive figures for deforestation in the previous year.

But this year the Amazon Fund's technical committee, along with its steering committee, COFA, were abolished by the Bolsonaro government on 11 April as part of a sweeping move to dissolve some 600 bodies, most of which had NGO involvement. The Bolsonaro government views NGO work in Brazil as a conspiracy to undermine Brazil's sovereignty.

The Brazilian government then demanded far-reaching changes in the way the fund is managed, as documented in a previous article. As a result, the Amazon Fund's technical committee has been unable to meet; Norway says it therefore cannot continue making donations without a favorable report from the committee.

Archer Daniels Midland soy silos in Mato Grosso along the BR-163 highway, where Amazon rainforest has largely been replaced by soy destined for the EU, UK, China and other international markets.

Thaís Borges.

An Uncertain Future

The Amazon Fund was announced during the 2007 United Nations Climate Change Conference in Bali, during a period when environmentalists were alarmed at the rocketing rate of deforestation in the Brazilian Amazon. It was created as a way of encouraging Brazil to continue bringing down the rate of forest conversion to pastures and croplands.

Government agencies, such as IBAMA, Brazil's environmental agency, and NGOs shared Amazon Fund donations. IBAMA used the money primarily to enforce deforestation laws, while the NGOs oversaw projects to support sustainable communities and livelihoods in the Amazon.

There has been some controversy as to whether the Fund has actually achieved its goals: in the three years before the deal, the rate of deforestation fell dramatically but, after money from the Fund started pouring into the Amazon, the rate remained fairly stationary until 2014, when it began to rise once again. But, in general, the international donors have been pleased with the Fund's performance, and until the Bolsonaro government came to office, the program was expected to continue indefinitely.

Norway has been the main donor (94 percent) to the Amazon Fund, followed by Germany (5 percent), and Brazil's state-owned oil company, Petrobrás (1 percent). Over the past 11 years, the Norwegians have made, by far, the biggest contribution: R$3.2 billion ($855 million) out of the total of R$3.4 billion ($903 million).

Up till now the Fund has approved 103 projects, with the dispersal of R$1.8 billion ($478 million). These projects will not be affected by Norway's funding freeze because the donors have already provided the funding and the Brazilian Development Bank is contractually obliged to disburse the money until the end of the projects. But there are another 54 projects, currently being analyzed, whose future is far less secure.

One of the projects left stranded by the dissolution of the Fund's committees is Projeto Frutificar, which should be a three-year project, with a budget of R$29 million ($7.3 million), for the production of açai and cacao by 1,000 small-scale farmers in the states of Amapá and Pará. The project was drawn up by the Brazilian NGO IPAM (Institute of Environmental research in Amazonia).

Paulo Moutinho, an IPAM researcher, told Globo newspaper: "Our program was ready to go when the [Brazilian] government asked for changes in the Fund. It's now stuck in the BNDES. Without funding from Norway, we don't know what will happen to it."

Norway is not the only European nation to be reconsidering the way it funds environmental projects in Brazil. Germany has many environmental projects in the Latin American country, apart from its small contribution to the Amazon Fund, and is deeply concerned about the way the rate of deforestation has been soaring this year.

The German environment ministry told Mongabay that its minister, Svenja Schulze, had decided to put financial support for forest and biodiversity projects in Brazil on hold, with €35 million ($39 million) for various projects now frozen.

The ministry explained why: "The Brazilian government's policy in the Amazon raises doubts whether a consistent reduction in deforestation rates is still being pursued. Only when clarity is restored, can project collaboration be continued."

Bauxite mines in Paragominas, Brazil. The Bolsonaro administration is urging new laws that would allow large-scale mining within Brazil's indigenous reserves.

Hydro / Halvor Molland / Flickr

Alternative Amazon Funding

Although there will certainly be disruption in the short-term as a result of the paralysis in the Amazon Fund, the governors of Brazil's Amazon states, which rely on international funding for their environmental projects, are already scrambling to create alternative channels.

In a press release issued yesterday Helder Barbalho, the governor of Pará, the state with the highest number of projects financed by the Fund, said that he will do all he can to maintain and increase his state partnership with Norway.

Barbalho had announced earlier that his state would be receiving €12.5 million ($11.1 million) to run deforestation monitoring centers in five regions of Pará. Barbalho said: "The state governments' monitoring systems are recording a high level of deforestation in Pará, as in the other Amazon states. The money will be made available to those who want to help [the Pará government reduce deforestation] without this being seen as international intervention."

Amazonas state has funding partnerships with Germany and is negotiating deals with France. "I am talking with countries, mainly European, that are interested in investing in projects in the Amazon," said Amazonas governor Wilson Miranda Lima. "It is important to look at Amazônia, not only from the point of view of conservation, but also — and this is even more important — from the point of view of its citizens. It's impossible to preserve Amazônia if its inhabitants are poor."

Signing of the EU-Mercusor Latin American trading agreement earlier this year. The pact still needs to be ratified.

Council of Hemispheric Affairs

Looming International Difficulties

The Bolsonaro government's perceived reluctance to take effective measures to curb deforestation may in the longer-term lead to a far more serious problem than the paralysis of the Amazon Fund.

In June, the European Union and Mercosur, the South American trade bloc, reached an agreement to create the largest trading bloc in the world. If all goes ahead as planned, the pact would account for a quarter of the world's economy, involving 780 million people, and remove import tariffs on 90 percent of the goods traded between the two blocs. The Brazilian government has predicted that the deal will lead to an increase of almost $100 billion in Brazilian exports, particularly agricultural products, by 2035.

But the huge surge this year in Amazon deforestation is leading some European countries to think twice about ratifying the deal. In an interview with Mongabay, the German environment ministry made it very clear that Germany is very worried about events in the Amazon: "We are deeply concerned given the pace of destruction in Brazil … The Amazon Forest is vital for the atmospheric circulation and considered as one of the tipping points of the climate system."

The ministry stated that, for the trade deal to go ahead, Brazil must carry out its commitment under the Paris Climate agreement to reduce its greenhouse gas emissions by 43 percent below the 2005 level by 2030. The German environment ministry said: If the trade deal is to go ahead, "It is necessary that Brazil is effectively implementing its climate change objectives adopted under the [Paris] Agreement. It is precisely this commitment that is expressly confirmed in the text of the EU-Mercosur Free Trade Agreement."

Blairo Maggi, Brazil agriculture minister under the Temer administration, and a major shareholder in Amaggi, the largest Brazilian-owned commodities trading company, has said very little in public since Bolsonaro came to power; he's been "in a voluntary retreat," as he puts it. But Maggi is so concerned about the damage Bolsonaro's off the cuff remarks and policies are doing to international relationships he decided to speak out earlier this week.

Former Brazil Agriculture Minister Blairo Maggi, who has broken a self-imposed silence to criticize the Bolsonaro government, saying that its rhetoric and policies could threaten Brazil's international commodities trade.

Senado Federal / Visualhunt / CC BY

Maggi, a ruralista who strongly supports agribusiness, told the newspaper, Valor Econômico, that, even if the European Union doesn't get to the point of tearing up a deal that has taken 20 years to negotiate, there could be long delays. "These environmental confusions could create a situation in which the EU says that Brazil isn't sticking to the rules." Maggi speculated. "France doesn't want the deal and perhaps it is taking advantage of the situation to tear it up. Or the deal could take much longer to ratify — three, five years."

Such a delay could have severe repercussions for Brazil's struggling economy which relies heavily on its commodities trade with the EU. Analysists say that Bolsonaro's fears over such an outcome could be one reason for his recently announced October meeting with Chinese President Xi Jinping, another key trading partner.

Maggi is worried about another, even more alarming, potential consequence of Bolsonaro's failure to stem illegal deforestation — Brazil could be hit by a boycott by its foreign customers. "I don't buy this idea that the world needs Brazil … We are only a player and, worse still, replaceable." Maggi warns, "As an exporter, I'm telling you: things are getting very difficult. Brazil has been saying for years that it is possible to produce and preserve, but with this [Bolsonaro administration] rhetoric, we are going back to square one … We could find markets closed to us."

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