The respiratory system includes the nose, throat, and lungs, which are all affected by the flu (influenza). Although influenza is frequently referred to as the flu, it differs from stomach "flu" viruses that cause vomiting and diarrhoea.
 
Most flu sufferers recover on their own. But occasionally, influenza and its side effects might be fatal.

Different Flu Types:

Type A Flu Virus

It is more frequent for people to experience the symptoms of this type of flu. This flu virus frequently inhabits wild birds as hosts.

The widespread flu epidemics are typically brought on by the type A flu virus, which is continually evolving. The most typical flu hot spots are objects that an infected person has touched and recent locations they have been, particularly sneezing sites.

Type B Flu Virus

Type B flu can occasionally be much more dangerous than type A Flu, even though it may elicit a less acute reaction. They do not cause pandemics.

Type C Flu Virus

The influenza C virus can also be detected in humans. However, they are less severe than either type A or type B. The influenza type C viruses often do not cause severe illness in humans. Flu viruses of type C do not start epidemics.

Type A Flu Virus

They are not known to infect people.

Causes
 
Flu is brought on by the influenza virus. The three most prevalent forms of influenza that affect people are A, B, and C. The symptoms of influenza A and B are more severe and are seasonal (the majority of cases occur in the winter). Influenza C doesn't have severe symptoms and isn't seasonal; it affects around the same number of people all year long.

Both H1N1 ("swine flu") and bird flu are Influenza A subtypes.

Symptoms
 
The flu may initially appear to be a typical cold with a runny nose, sneezing, and sore throat. Colds typically take time to break. However, the flu often strikes suddenly. And while having a cold might be unpleasant, having the flu typically makes you feel much worse.
 
Flu symptoms typically include:
a) Fever
b) Aching muscles
c) Chills and sweats
d) Headache
e) Dry, persistent cough
f)  Shortness of breath
g) Tiredness and weakness
h) Runny or stuffy nose
i)  Sore throat
j)  Eye pain
k) Vomiting and diarrhea are common, but more so in kids than in adults
 
Diagnosis
 
By taking note of your symptoms and examining a sample of nasal mucus, your doctor can determine whether you have the flu. They will insert a long stick with a soft tip (swab) into your nose to check for influenza. Results would come back in a day or two.
 
The flu isn't that serious
 
Untreated, the flu can cause you to become seriously unwell for days to weeks, end up in the hospital, and even cause death. Different from a cold, symptoms of the flu can appear abruptly and include fever, chills, sore throat, runny or stuffy nose, muscle or body pains, headaches, lethargy, and occasionally vomiting and diarrhea. Additionally, the flu can make you vulnerable to a more severe form of bacterial pneumonia, which might have detrimental effects on how well your lungs supply oxygen to the rest of your body.
 
Getting the flu shot annually is the most effective approach to avoid getting the flu. Immune system training from vaccinations teaches your body to spot diseases and fight them off before you become ill. You should get vaccinated annually since the influenza virus can alter (mutate) slightly each year.
 
The flu vaccine lowers your risk of developing a serious illness, even if you end up becoming sick with a different strain of the virus than the one in the vaccine.