Influenza Virus

Influenza, commonly called "the flu," is an illness caused by RNA viruses that infect the respiratory tract of many animals, birds, and humans.

In most people, the infection results in the person getting fever, cough, headache, and malaise (tired, no energy); some people also may develop a sore throat, nausea, vomiting, and diarrhoea. The majority of individuals has symptoms for about one to two weeks and then recovers with no problems. However, compared with most other viral respiratory infections, such as the common cold, influenza (flu) infection can cause a more severe illness with a mortality rate (death rate) of about 0.1% of people who are infected with the virus.

Typical symptoms of flu include
•    fever (usually 100 F-103 F in adults and often even higher in children),
•    respiratory symptoms such as cough, sore throat,
•    runny or stuffy nose,
•    headache,
•    muscle aches, and
•    fatigue, sometimes extreme.
Although nausea, vomiting, and diarrhoea can sometimes accompany influenza infection, especially in children, gastrointestinal symptoms are rarely prominent. The term "stomach flu" is a misnomer that is sometimes used to describe gastrointestinal illnesses caused by other microorganisms.

Most people who get the flu recover completely in one to two weeks, but some people develop serious and potentially life-threatening medical complications, such as pneumonia.
In an average year, influenza is associated with about 36,000 deaths nationwide and many more hospitalizations. Flu-related complications can occur at any age; however, the elderly and people with chronic health problems are much more likely to develop serious complications after the conventional influenza infections than are younger, healthier people.

What is the key to flu prevention? Flu vaccine
Much of the illness and death caused by influenza can be prevented by annual influenza vaccination. Flu vaccine (influenza vaccine made from inactivated and sometimes attenuated [non-infective] virus) is specifically recommended for those who are at high risk for developing serious complications as a result of influenza infection.
These high-risk groups for conventional flu include all people aged 65 years or older and people of any age with chronic diseases of the heart, lung, or kidneys; diabetes; immunosuppression; or severe forms of anemia.
•    pregnant women,
•    people who live with or care for children younger than 6 months of age,
•    health-care and emergency-services personnel,
•    people between the ages of 6 months through 24months of age and children 5-18 years of age who have chronic medical problems, and
•    people from 25-64 years of age who are at higher risk for novel H1N1 because of chronic health disorders or compromised immune systems.

However, with the novel H1N1 flu, the groups listed below are indicated as being at high risk and should obtain the novel H1N1 vaccine as soon as it is available to them:
Other groups for whom conventional flu vaccine is specifically recommended are residents of nursing homes and other chronic care facilities housing patients of any age with chronic medical conditions. Influenza vaccine is also recommended for people who are in close or frequent contact with anyone in the high-risk groups defined above.
These people include health-care personnel and volunteers who work with high-risk patients and people who live in a household with a high-risk person.
Why should the flu vaccine be taken every year?
Although only a few different influenza virus strains circulate at any given time, people may continue to become ill with the flu throughout their lives. The reason for this continuing susceptibility is that influenza viruses are continually mutating, through the mechanisms of antigenic shift and drift described above.
Each year, the vaccine is updated to include the most current influenza virus strains that are infecting people worldwide. The fact that influenza viral genes continually change is one of the reasons vaccine must be taken every year. Another reason is that antibody produced by the host in response to the vaccine declines over time, and antibody levels are often low one year after vaccination.

What are some treatments an individual can do at home for the flu?
First, individuals should be sure they are not members of a high-risk group that is more susceptible to getting severe flu symptoms. Check with your physician if you are unsure if you are a higher risk person. Fever can be treated with over-the counter medication. Cough can be suppressed by cough drops and over-the-counter cough syrup. If an individual's symptoms at home get worse, their doctor should be notified.

However, there are situations in which some flu outbreaks are severe. These severe outbreaks occur when the human population is exposed to a flu strain against which the population has little or no immunity because the virus has become altered in a significant way. Unusually severe worldwide outbreaks (pandemics) have occurred several times in the last hundred years since influenza virus was identified in 1933. By an examination of preserved tissue, the worst influenza pandemic (also termed the Spanish flu) occurred in 1918 when the virus caused between 40-100 million deaths worldwide, with a mortality rate estimated to range from 2%-20%.
In April 2009, a new influenza strain against which the world population has little or no immunity was isolated from humans in Mexico. It quickly spread throughout the world so fast that the WHO declared this new flu strain (termed novel H1N1 influenza A swine flu, often shortened to H1N1 or swine flu) as the cause of a pandemic on June 11, 2009. This was the first declared flu pandemic in 41 years.
 
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