Influenza
Influenza, also known as the flu, is a disease of humans, birds and mammals that is caused by RNA viruses of the influenza virus class.  The most common symptoms include fever, chills, sore throat, muscle aches, cough, weakness, headache and generalized malaise.  When it becomes severe, it causes a potentially fatal pneumonia, especially in young people and older individuals.  Influenza is a much more severe disease than the common cold, even though the symptoms can be similar.  Influenza can affect the GI tract, with nausea and vomiting. 
Influenza is generally transmitted through infected mammals through air droplets such as sneezing or coughing.  Bird droppings can also transmit the virus.  Any kind of saliva, feces, nasal secretions and blood exposure can transmit the virus.  The flu continues to be infectious at human body temperature for a total of one week.  It is infectious at lower temperatures for a longer period of time.  Certain soaps and disinfectants can inactivate the virus. 
The flu travels around the world in what is known as seasonal epidemics and results in the demise of hundreds of thousands of victims per year.  There are pandemic years with severe influenza cases where millions of people die.   For this reason, vaccinations against the virus are given to peoples in most developed countries as well as to farmed birds.  The vaccination usually contains two type A influenza strains and one type B virus strain.  The types of strains used from year to year, depending on anticipated types of influenza for the upcoming year. 
History of Influenza
The symptoms we attribute to influenza were described as early as 2400 years ago by Hippocrates.   Numerous epidemics and pandemics have occurred throughout the years.  It is difficult, however, to know which pandemics were caused by influenza and which were due to another similar illness. The first true pandemic of influenza occurred in 1580, wiping out several Spanish cities.  The most infamous of pandemic flu attacks occurred in the winter of 1918-19 and is believed to have killed up to a hundred million people. This was a global flu, extending from the Arctic to even remote islands of the Pacific. About 2-20 percent of sufferers died from this flu.  There have been later pandemics in the 20th century, but these have not been so severe. 
Types of Influenza Virus
There are different types of influenza virus.  The first is influenza A.  Its natural hosts are wild aquatic birds.  Influenza B is less common than influenza A and is found exclusively in humans.  Influenza C infects both humans and pigs and is responsible for local epidemics. 
Diagnosis
Influenza tends to last much longer and be more severe than the common cold.  It takes at least one to two weeks to recover from influenza.  Unlike the common cold, influenza can be fatal, especially for those who are elderly, weak or very young.  Those with emphysema, asthma or chronic bronchitis are particularly at risk for fatal influenza.  Smoking is another risk factor that increases influenza’s mortality. 
The diagnosis is usually made by clinical findings.  It can start quite suddenly with chills and fever.  Most sufferers are bedridden for several days and suffer from bodily aches and pains.  There is coughing and sneezing, tiredness, frontal headache, nasal congestion, watery eyes, and abdominal pain.  It is important to diagnose the disease as quickly as possible because antiviral agents work best when given early in the disease. 
Laboratory test exist that are about 95 percent specific and 75 percent sensitive that are useful during the influenza season to decide who has the disease and who just has the common cold.  The disease peaks in the winter season and there are actually two seasons: one from the Northern Hemisphere and one from the Southern Hemisphere. 
Prevention
The best prevention is vaccination, which is often recommended for those at highest risk for the disease. Protection is effective for about two years.  Vaccines usually protect against more than one strain of the influenza virus.
Treatment
Sufferers are to get a lot of rest, consume plenty of fluids and avoid alcohol and tobacco.  They can take acetaminophen.  Children should not take aspirin because of the incidence of Reye’s Syndrome.  Antibiotics have no effect unless there is a secondary pneumonia from the influenza.   
There is evidence that the replication of the virus is dependent on the redox state of the host cell meaning that the use of glutathione can be a treatment for the influenza virus.