Encyclopedia of Health and Medicine

Risk Factors and Preventive Measures
People at highest risk for influenza are the very
young, the very old, and those who have comproinfluenza
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causes upper respiratory symptoms. Influenza
viruses rapidly adapt and mutate, which gives
them the perpetual ability to cause illness. There
are three types of human influenza VIRUS—
influenza A, influenza B, and influenza C.
Influenza A viruses are primarily responsible for
annual outbreaks of the flu, though influenza B
viruses also cause illness.
Some strains of influenza A infect humans and
some strains infect animals such as pigs (swine
influenza virus) and poultry (avian influenza
virus). Strains of influenza A that infect animals
can sometimes mutate in ways that permit them
to cross over to infect people, as happened in 1918
with the world’s most severe influenza pandemic,
known as the Spanish flu (because the first cases
occurred in Spain), which researchers today
believe mutated from a variety of swine influenza
virus.
Symptoms and Diagnostic Path
Influenza is an illness of the upper respiratory
tract, the symptoms of which tend to emerge rapidly
and full-force. Symptoms of influenza include
• high FEVER (102ºF or higher)
• severe HEADACHE
• muscle aches and JOINT PAIN
• nonproductive COUGH
• sore THROAT
• nasal and sinus congestion
Some people, especially young children, may
experience NAUSEA and VOMITING. However, gastrointestinal
symptoms are not characteristic of
influenza, and their prominent presence suggests
a different infection. There are several tests available
for influenza, including rapid tests that the
doctor can use in the office as well as blood tests.
Treatment Options and Outlook
Most often, the flu simply runs its course and
treatment targets relieving symptoms such as
fever and aches. Rest, fluids, and nutritious foods
are important for helping the body to fight the
virus. Secondary bacterial infections and other
complications can occur and require appropriate
treatment. ANTIBIOTIC MEDICATIONS are not effective
for treating viruses, though the doctor may prescribe
an antibiotic to treat a secondary bacterial
infection that develops, such as PNEUMONIA or STREP
THROAT. The most common complication of
influenza is PNEUMOCOCCAL PNEUMONIA, a bacterial
infection for which there is a one-time vaccine
(though people who have lung disorders or respiratory
compromise may need a second vaccine 10
years after the first vaccine).
The flu vaccine IMMUNIZATION remains the
frontline of treatment for influenza. Each year
researchers determine the two strains of influenza
A and one strain of influenza B most likely to
cause infection (based on complex algorithms of
historic and projected viral cycles). Manufacturers
then cultivate the three strains to create the year’s
VACCINE. This is a somewhat speculative approach,
however, and the actual strains of influenza that
surface may be entirely different. When the
strains are similar to those in the vaccine the vaccine
is highly effective in preventing or moderating
influenza infection. When the strains are not
at all close, the vaccine offers no protection from
influenza infection. Because the influenza virus so
rapidly mutates, each vaccine is effective only for
a single flu season.
Antiviral medications ANTIVIRAL MEDICATIONS
may shorten the course of illness and lessen the
severity of symptoms when taken within 48 hours
of the first symptoms and may prevent infection
with influenza after exposure to someone who
has the viral infection. Antiviral medications work
by interfering with the mechanisms viruses use to
alter the functions of their host cells, typically by
blocking the action of key enzymes or proteins
that the virus uses to instruct RNA to take over the
host cell. Some antiviral medications are effective
against influenza A (amantadine and rimantadine)
and others against influenza B (zanamivir and
oseltamivir). Further testament to the influenza
virus’s ability to mutate is the emergence of
influenza virus strains that are resistant to amantadine
and rimantadine.