various forms of influenza
viruses
Influenza is a viral infection of
the lungs characterized by fever, cough, and severe muscle aches. In the
elderly and infirm, it is a major cause of disability and death (often
as a result of secondary infection of the lungs by bacteria). Even in
the young and healthy, influenza produces a prostrating disease of a few
days duration and one not soon forgotten.
Influenza is not
- a case of low fever
and sniffles that keeps you home in bed for a day
- a gastrointestinal
upset ("stomach flu")
Influenza was
responsible for the most devastating plague in human history — the "Spanish"
flu that swept around the world in 1918 killing 675,000 people in the
U.S. and an estimated 20–50 million people worldwide. (A disease that
attacks a large fraction of the population in every region of the world
is called a pandemic.) (It is uncertain where the flu first appeared,
but it certainly wasn't in Spain.)
No one at the time even knew what disease
agent was causing the pandemic. Not until 1930 (in pigs) and 1933 (in
humans) was it established that influenza is caused by a virus.
This electron micrograph (courtesy of Dr.
K. G. Murti) shows several influenza virus particles (at a magnification
of about 284,000x). The surface projections are molecules of hemagglutinin
and neuraminidase (see below).
There are three types
of influenza:
Common but seldom
causes disease symptoms
Often causes sporadic
outbreaks of illness, especially in residential communities like nursing
homes.
Responsible for
regular outbreaks, including the one of 1918. Influenza A viruses also
infect domestic animals (pigs, horses, chickens, ducks) and some wild
birds.
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Types of influenza:
Influenza is
an acute infectious disease.
- Influenza A
- Influenza B
- Influenza C
Infections
with influenza are usually more severe than those with other respiratory
viruses and involve a combination of respiratory and constitutional
symptoms.
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Influenza
Viruses
