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Influenza
Influenza (or as it is
commonly known, the flu) is a contagious disease caused by an RNA virus
of the orthomyxoviridae family. The name comes from the old medical
belief in unfavourable astrological influences as the cause of the
disease.
Types
There are three types of the virus:
1. Influenza A viruses that infect mammals (humans, pigs, ferrets,
horses) and birds
2. Influenza B viruses that infect only humans
3. 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
* Headache
* Tiredness (can be extreme)
* Dry cough
* Sore throat
* Nasal congestion and sneezing
* 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.
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What
You Should Know
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Uncomplicated
influenza gets better with or without treatment, but may
cause substantial discomfort and limitation of activity before getting
better. Complications of influenza can include bacterial infections,
viral pneumonia, and cardiac and other organ system abnormalities.
People with chronic medical conditions may have increased risk of
complications when they get influenza. Many other diseases, including
serious infections such as rapidly progressive bloodstream infections,
may start with symptoms that resemble influenza and may need to be
considered in treatment decisions.
Rapid laboratory tests can help in
detecting influenza but do not exclude the possibility of other
illnesses or take the place of clinical evaluation.
Complications
of influenza, and other illnesses that resemble
influenza, may require different treatment and may need urgent medical
attention. Use of antiviral drugs does not eliminate the risk of
complications, and some complications (as well as other medical
conditions that could be confused with influenza) can be
life-threatening. In addition, influenza viruses can become resistant
to specific anti-influenza antiviral drugs, and all of the drugs have
side effects. Therefore, if you have new symptoms during treatment, or
your symptoms persist or get worse during treatment, you should see
your health care provider.
Outbreaks of influenza occur every year and typically reach epidemic
levels during some part of the season. If a new variety of
influenza
starts to be transmitted rapidly between people, it can cause extremely
widespread illness known as a pandemic. Depending on the strain
of
influenza causing a pandemic, antiviral drugs may have varying levels
of usefulness.
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