A virus called an Orthomyxovirus causes influenza. Often called flu, sometimes-even grippe. It is a very contagious disease, and it infects many parts of our bodies. This also includes are lungs. A person can get influenza if someone coughs, sneezes, or even talks around you while they are infected. Influenza is sometimes considered serious in some cases but can be prevented and treated.
When you get the "flu" in the lungs, the lining of the respiratory tract is damaged by becoming swollen and inflamed. But the damage is not always permanent, and tissue heals within a couple of weeks. It is a respiratory disease, even though it infects the whole body.
The victims' symptoms usually are fever, chills, weakness, loss of appetite and body, head, back, arm, and leg ache. If you have the disease you may also suffer sore throat, a dry cough, nausea, and burning red eyes. Usually the victim will have nasal congestion and mucus discharge. The fever can reach to about 104*F but it only lasts about 2-3 days then it recedes. Occasionally in more severe cases there will also be gastrointestinal upset. In short, after all these horrible symptoms the patient still feels exhausted a series of days after the flu is gone.
Healthy people have nothing to worry about really when it comes to influenza. It is a moderately severe illness and people are usually back on their feet after a week or so. That is not the case for people that are at high risk. People at high risk receive a greater impact from the disease, like complications. Some complications these people at high-risk face are sinus and inner ear inflammation as well bacterial pneumonia (yeah, and I'm sure that sounds real pleasant). Unfortunately, most complications end with bacterial infections. In the end if you don't get treated influenza can be severe and fatal.
People that are at a high risk are ones that have chronic lung disease such as asthma, emphysema, chronic bronchitis,...