Influenza

Influenza (or as it is commonly known, the flu) is a contagious\ndisease caused by an RNA virus of the\northomyxoviridae family. \nThe name comes from the old medical belief in unfavourable astrological\ninfluences as the cause of the disease.

Table of contents

1 Types 2 Symptoms 3 Variability 4 Prevention 5 Treatment 6 The myth of the "stomach flu" 7 See also 8 External links

Types

There are three types of the virus:\n* Influenza A viruses that infect mammals (humans, pigs, ferrets, horses) and birds\n* Influenza B viruses that infect only humans\n* Influenza C viruses that infect only humans The A type of influenza virus is the type most likely to cause epidemics and pandemics. This is because the influenza A virus can undergo antigenic shift and present a new immune target to susceptible people. Populations tend to have more resistance to influenza B and C because they only undergo antigenic drift and have more similarity with previous strains. Where a finer grained classification of the virus strain is needed, this is done by reference to the structural forms of two viral proteins (haemaglutinin and neuraminidase) that are essential to the virus' life cycle. Thus one might speak of H1N1 or H3N2 viral strains.

Symptoms

The virus attacks the respiratory tract, is transmitted from person to person by droplets, and causes the following symptoms:

• Fever\n* Headache\n* Tiredness (can be extreme)\n* Dry cough\n* Sore throat\n* Nasal congestion and sneezing\n* Body aches

Although a lot of people in the western world will often call a heavy cold "flu", you know when you have got real influenza as its effects are much more severe and last longer. Typically influenza takes about 1-2 weeks to recover from. Flu can be a killer disease, especially for the weak, old or chronically ill. Some flu pandemics have killed millions of people, for example the "Spanish Flu" pandemic of 1918-1919, which is believed to have killed more people in total than World War I. Most people who get influenza will recover in one to two weeks, but some people will develop life-threatening complications (such as pneumonia) as a result of the flu. Millions of people in the United States (about 10% to 20% of U.S. residents) will get influenza each year. An average of about 36,000 people per year in the United States die from influenza, and 114,000 per year have to be admitted to the hospital as a result of influenza. Anyone can get the flu (even healthy people), and serious problems from influenza can happen at any age. People age 65 years and older, people of any age with chronic medical conditions, and very young children are more likely to get complications from influenza. Pneumonia, bronchitis, and sinus and ear infections are three examples of complications from flu. The flu can make chronic health problems worse. For example, people with asthma may experience asthma attacks while they have the flu, and people with chronic congestive heart failure may have worsening of this condition that is triggered by the flu.

Variability

Influenza is an extremely variable disease: similar viruses are found in pigs and domestic fowl. In areas where there are high concentrations of humans, pigs and birds in close proximity, such as parts of Asia, simultaneous infections across species enable genetic material to be exchanged between the various strains of flu. This appears to be the principal method by which new infectious strains arise. It is believed that sooner or later, a recombination may occur to produce a strain as lethal as the 1918 virus. In late 1997, a new strain of avian influenza (also known as bird flu) originating from chickens infected 18 people in Hong Kong, of whom 6 died. This strain did not appear to be readily transmissible from human to human, but such a high mortality rate, and the possibility of a further recombination to make it more infectious, meant that the risk was considered so great that all domestic poultry in Hong Kong was slaughtered. Avian influenza transmissible to humans resurfaced in January 2004\nin Vietnam and Thailand.

Prevention

It is possible to get vaccinated against Influenza, however due to the high mutability of the virus the vaccine is usually only good for a year or so. The World Health Organization co-ordinates the contents of the vaccine each year to contain the most likely strains of the virus to attack the next year. The vaccine is usually recommended for anyone in a high-risk group who may suffer complications from a real flu attack.

Treatment

Antiviral treatments :\n* Amantadine\n* Rimantadine\n* Oselatamivir

The myth of the "stomach flu"

Many people use the term "stomach flu" to describe illnesses with nausea, vomiting, or diarrhea. These symptoms can be caused by many different viruses, bacteria, or even parasites. While vomiting, diarrhea, and being nauseous or sick to your stomach can sometimes be related to influenza, particularly in children, these problems are rarely the main symptoms of the infection. The flu is a respiratory disease and not a stomach or intestinal disease.

See also

• Infectious diseases\n* Pandemic

External links

• WHO flu fact sheet\n* CDC flu page

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Some of this article has been taken from the public domain CDC publication http://www.cdc.gov/ncidod/diseases/flu/fluinfo.htm Category:Infectious diseases \n\n\n\n\n\n\nzh-tw:流行性感冒