Influenza, or flu, is an acute respiratory infection caused by a variety of influenza
viruses. The most familiar aspect of flu is the way it can "knock you off your feet" as it
sweeps through entire communities, usually during the winter. Flu differs in several ways
from the common cold, a respiratory infection also caused by viruses.
Outbreaks of flu usually begin abruptly. As the disease spreads through communities,
the number of cases peaks in about 3 weeks and subsides after another 3 or 4 weeks. Twenty
to fifty percent of a population may be affected, with the highest incidence in 5 to
14 year olds. Schools are an excellent place for transmission of flu viruses, so that
families with school-age children have a higher rate of infection than other families,
with an average of one-third of the family members infected each year.
Besides the rapid onset of the outbreaks and the large numbers of people affected, flu
is important because of the seriousness of the complications that can develop. Most people
who contract the disease recover within a week (although they may tire easily for awhile).
However, for elderly people, newborn babies, and people with certain chronic illnesses,
flu and its complications can be life-threatening.
Viruses that cause flu spread primarily from person to person, especially by coughing
and sneezing. Flu viruses can enter the body through the mucous membranes of the eyes,
nose, or mouth. After a person has been infected with the virus, symptoms usually appear
within 2 to 4 days. The infection is considered contagious for another 3 to 4 days after
symptoms appear.
The greatest risk of infection is in highly populated areas, where people live in
crowded conditions, and in schools. Isolating people with flu symptoms is not an effective
means of disease control because flu can be spread by someone whose symptoms are not yet
apparent.
Flu is usually signaled by headache, chills, and dry cough, which are followed rapidly
by body aches and fever. Typically, the fever starts declining on the second or third day
of the illness. It is then that the upper respiratory symptoms become noticeable-nasal
congestion and sore throat. Flu almost never causes gastrointestinal symptoms; the illness
that people often call "stomach flu" is not influenza.
Once a person has the flu, treatment usually consists of resting in bed, drinking
plenty of fluids, and taking medication such as aspirin or acetaminophen to relieve fever
and discomfort. Children with flu should not take aspirin. Antibiotics are not effective
against flu viruses.
The drug rimantadine can be used to treat influenza type A virus infections in adults.
It has no effect on influenza type B infections. When taken within 48 hours after the
onset of illness, it reduces the duration of fever and other symptoms and allows flu
sufferers to return to their daily routines more quickly.
Rimantadine is a derivative of the drug amantadine, which also can prevent and treat
flu infection. Amantadine, however, is more likely to cause side effects such as
lightheadedness and inability to sleep more often than is rimantadine.
Flu complications (which can either accompany or follow the illness) generally result
from bacterial infections in the lower respiratory tract. The ensuing pneumonia usually is
caused by pneumococcal bacteria, but infections with staphylococci, streptococci, and
Haemophilus influenzae type b can occur.
Symptoms of complications usually appear after the flu patient starts feeling better.
This brief period of improvement is followed by the sudden onset of high fever, shaking
chills, chest pain with each breath, and coughing that produces thick,
yellow-greenish-colored sputum. Although most people with pneumonia recover after
treatment with antibiotics, some pneumonia-causing organisms are resistant to these drugs.
A neurologic disease known as Reye's syndrome sometimes develops in a small number of
children and adolescents who are recovering from flu. Reye's syndrome usually is signaled
by the onset of nausea and vomiting, but the progressive mental changes (such as confusion
or delirium) cause the greatest concern. The syndrome is associated with the use of
aspirin, which often is used in medications for relieving the pain or fever of flu.
Although fewer than 3 children per 100,000 with flu develop Reye's syndrome, one should
consult a physician before administering aspirin or aspirin-containing products to
children. Use of acetaminophen is not associated with Reye?s syndrome.
The first flu virus was identified in the 1930's. Since then, scientists have
classified flu viruses into types A, B, and C. Type A is the most prevalent and is
associated with the most serious epidemics. Type B outbreaks also can reach epidemic
levels, but the disease it produces generally is milder than that caused by type A. Type C
viruses, on the other hand, never have been connected with a large epidemic.
Unlike antigens of other viruses, the surface antigens of flu viruses change
periodically. These changes circumvent antibodies and complicate vaccine development.
The hemagglutinin molecules of flu viruses are highly unstable and often mutate during
replication. These periodic changes result in new strains of viruses with altered surface
antigens. Persons with antibodies stimulated either by previous infection or vaccination
are not protected from infection with new strains of flu virus.
Slight changes in flu virus antigens are referred to as antigenic drifts. Every few
years, at unpredictable intervals, a major change, or antigenic shift, occurs. Shifts have
been observed only in influenza A viruses.
Pandemics are the result of antigenic shifts and are associated with severe illness and
significant mortality on a global scale. Within this century, at least five pandemics and
numerous epidemics (regional outbreaks involving fewer people) have occurred. For example,
antigenic shifts were evident in the 1957 outbreak known as the Asian flu, which affected
huge numbers of people, and in the 1968 outbreak of the virulent Hong Kong strain.
Each year, scientists formulate a new vaccine made from inactivated (killed) influenza
viruses. The preparation is based on the strains in circulation at the time, yet includes
those A and B viruses expected to circulate the following winter. Sometimes, an
unpredicted new strain may appear after the vaccine has been manufactured and distributed,
resulting in infection even among those who received flu vaccine. Usually, however, the
disease is milder because the vaccine will provide some protection.
Since the immune system takes time to respond to vaccination, the inactivated vaccine
should be given 6 to 8 weeks before flu season begins in order to stimulate enough
antibodies to prevent infection or reduce the severity of the illness. The vaccine itself
cannot cause flu, but someone could become exposed and infected soon after vaccination,
before antibodies develop.
The vaccine, however, may cause side effects, especially in children who previously
have not been exposed to the flu virus. The most common side effect in children and adults
is soreness at the site of the vaccination. Others include fever, tiredness and sore
muscles that may begin 6 to 12 hours after vaccination and may last for up to 2 days.
Viruses for vaccine production are grown in chicken eggs and then inactivated with a
chemical so that they are no longer infectious. People who are allergic to eggs should not
receive flu vaccine since some egg protein may be present in the vaccine.
Certain herbs have anti-viral benefits:
- Echinacea
- Goldenseal
- Garlic
- Elderberry
