INFORMATION ON FLU

Flu(Influenza)

Natural Cold & Flu Remedies Slideshow

Medical Author: Charles Davis, MD, PhDMedical Editor: Melissa Conrad Stöppler, MD
What is influenza?
What are the causes of the flu?
What are flu symptoms?
Is there any treatment for the flu?
Why must the flu vaccine be taken every year?
When should you receive the flu vaccine?
What is the bird flu?
Do antiviral agents protect you from the flu?
Where can I find additional information about the flu?
Flu (Influenza) At A Glance
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Influenza, or the "flu," is a illness of the breathing system (respiratory system) and muscles caused by a virus. While a vaccine is available to prevent the flu, its effectiveness varies according to the degree of match between the viral strains used to prepare the vaccine and those strains actually in circulation in a given year. Not everyone receives the flu vaccine, and even some of those who do can develop symptoms of the flu.
Mild cases of the flu may seem like common colds. But most cases of the flu can be distinguished from colds because the symptoms (cough, muscle aches and pains, sore throat, fatigue, and headache) are more severe than those of the common cold. Flu symptoms also tend to occur suddenly and include high fevers (temperatures of 101 degrees F or more). In children, fevers are typically even higher than those in adults.
The flu is a serious illness that can be fatal in people whose immune systems are weakened, the elderly, and those with chronic medical conditions. Even healthy people who develop the flu cannot work, attend school, or participate in normal activities for several days. Complications of the flu can develop in anyone and include pneumonia, ear infections, sinus infections, or bronchitis.
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What is influenza?
Influenza, commonly called "the flu," is an illness caused by viruses that infect the respiratory tract. Compared with most other viral respiratory infections, such as the common cold, influenza (flu) infection often causes a more severe illness with a mortality rate (death rate) of about 0.1% of people who are infected with the virus. Unusually severe worldwide outbreaks (pandemics) have occurred several times in the last 100 years since influenza virus was identified in 1933. By an examination of preserved tissue, the worst influenza pandemic occurred in 1918 when the virus caused between 40 to 100 million deaths with a mortality rate estimated to range from 2% to 20%.
Haemophilus influenzae is a bacterium that was incorrectly considered to cause the flu until the virus was demonstrated to be the correct cause in 1933. This bacterium can cause lung infections in infants and children, and it occasionally causes ear, eye, sinus, joint, and a few other infections, but not the flu.

What are the causes of the flu?
The flu (influenza) virusesInfluenza viruses are divided into three types, designated A, B, and C. Influenza types A and B are responsible for epidemics of respiratory illness that occur almost every winter and are often associated with increased rates of hospitalization and death. Influenza type C differs from types A and B in some important ways. Type C infection usually causes either a very mild respiratory illness or no symptoms at all; it does not cause epidemics and does not have the severe public health impact of influenza types A and B. Efforts to control the impact of influenza are aimed at types A and B, and the remainder of this discussion will be devoted only to these two types.

Influenza viruses continually change over time, usually by mutation (change in the viral RNA). This constant changing often enables the virus to evade the immune system of the host (humans, birds, and other animals) so that the host is susceptible to changing influenza virus infections throughout life. This process works as follows: a host infected with influenza virus develops antibody against that virus; as the virus changes, the "first" antibody no longer recognizes the "newer" virus and reinfection can occur. The first antibody may in some instances provide partial protection against reinfection with an influenza virus.