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Today, influenza is the name given to diseases caused by a specific family of viruses. The word comes from the Italian equivalent to the English word "influence" because, in an epidemic that broke out in Italy during the 18th Century, the common belief was that epidemics were caused the influence of the stars.

Influenza is a respiratory disease, but some of the symptoms involve more than the airways. These are the result of the immune system, which becomes mobilized to fight the infection.

People with weak immune systems, such as the elderly, or immune-compromised patients are vulnerable to more serious influenza. In these patients, the virus penetrates from the upper airways deeper into the lung, and the consequence can become severe and even fatal.


Symptoms of influenza in people overlap those of other respiratory diseases, and it requires confirmation by analysis to definitively diagnose influenza.

The symptoms vary between individuals but commonly include:

  • chills                                      
  • fever                                   
  • runny nose
  • sore throat
  • muscle pain
  • coughing
  • weakness
  • fatigue
  • headache
  • general discomfort


In otherwise healthy people, the symptoms can last four to seven days, but in vulnerable populations, the illness can be fatal.



There have been many influenza pandemics throughout history, resulting in millions of deaths.


Name of PandemicDateDeaths

1889-1890 Flu Pandemic

(Asiatic or Russian Flu)

1889 – 18901 million

1918 Flu Pandemic

(Spanish Flu)

1918-192020 to 100 million
Asian Flu1957 – 19581 to 1.5 million
Hong Kong Flu1968-19690.75 to 1 million
Russian Flu1977-1978no accurate count
2009 Flu Pandemic2009 -201018,000


Localized epidemics are also common, especially where people are in close contact.  Flu seasons are unpredictable and can be severe. 

According to the CDC, between 1976 and 2006, estimates of flu-associated death in the US range from 3,000 to 49,000 people.


Influenza Strains:

There are three types of Influenza virus, A, B and C, of which A is most common.

People are not the only animals to become infected with influenza. In fact type C and most of the known strains of influenza virus type A don't infect people at all. Birds, swine, horses, dogs, cats, and seals can be hosts to influenza virus. The transmission between wild fowl to domestic animals, such as poultry or pigs can catalyze the next pandemic, and Public Health Officials around the world track these outbreaks.