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Name: H1N1 Swine Flu
Description: Influenza
This casebook is published and has been read 731 times.
The author of this casebook has identified the following medical topics as being highly relevant to this casebook.
The first flu virus was identified in the 1930s. Since then,
scientists have classified influenza viruses into types A, B, and C.
Cause
You can get the flu if someone around you who has the flu coughs or sneezes. You can get the flu simply by touching a surface like a telephone or door knob that has been contaminated by a touch from someone who has the flu. The viruses can pass through the air and enter your body through your nose or mouth. If you've touched a contaminated surface, they can pass from your hand to your nose or mouth.
You are at greatest risk of getting infected in highly populated areas, such as in crowded living conditions and in schools.
If you get infected by the flu virus, you will usually feel symptoms
1 to 4 days later. You can spread the flu to others before your
symptoms start and for another 3 to 4 days after your symptoms appear.
The symptoms start very quickly and may include Typically, the fever begins to decline on the second or third day of
the illness. The flu almost never causes symptoms in the stomach and
intestines. The illness that some call “stomach flu” is not influenza.
You can have flu complications if you get a bacterial infection,
which can cause pneumonia in your weakened lungs. Pneumonia also can be
caused by the flu virus itself. Complications usually appear after you start feeling better. After a
brief period of improvement, you may suddenly get these symptoms Pneumonia can be a very serious and sometimes life-threatening
condition. If you have any of these symptoms, you should contact your
health care provider immediately to get the appropriate treatment. Reye's syndrome, a condition that affects the nerves, sometimes
develops in children and teenagers who are recovering from the flu.
Reye's syndrome begins with nausea and vomiting, but the progressive
mental changes (such as confusion or delirium) cause the greatest
concern. The syndrome often begins in young people after they take aspirin to
get rid of fever or pain. Although very few children develop Reye's
syndrome, you should consult a health care provider before giving
aspirin or products that contain aspirin to children. Acetaminophen
does not seem to be connected with Reye's syndrome. Newborn babies recently out of intensive care units are particularly vulnerable to suffering from flu complications.
Usually, health care providers diagnose the flu on the basis of
whether it is epidemic in the community and whether the person's
complaints fit the current pattern of symptoms. Health care providers
rarely use laboratory tests to identify the virus during an epidemic.
Health officials, however, monitor certain U.S. health clinics and do
laboratory tests to determine which type of flu virus is responsible
for the epidemic.
Health
care providers can prescribe medicines to help fight the flu. These
medicines are called antivirals and can be taken to treat or prevent
the flu. For example, flu antivirals can be given to treat someone who
just became sick (within 2 days). When the medicines are given to
someone who is already ill, the symptoms and time the person is sick
can be reduced. On the other hand, these same flu antiviral medicines
can be given to a well person who has been in contact with someone who
has the flu. Although this does not prevent you from getting the flu,
it does reduce your chances of catching it and passing it on to others.
By no means should these antiviral medicines be used in place of the
flu vaccine. Currently, there are four licensed
antivirals against influenza A and B in the United States. However,
only 2 of them are recommended by the CDC as a result of emerging
influenza A resistance to the other two, amantadine and rimantadine: For
these medicines to work well, you must take them within 48 hours after
the symptoms of flu appear. These medicines can reduce the length of
time that a fever and other symptoms last, and allow you more quickly
to return to your daily routine. Zanamivir and oseltamivir are the first of a new class of antiviral drugs called neuraminidase inhibitors. The
surfaces of influenza viruses are dotted with neuraminidase proteins.
Neuraminidase, an enzyme, breaks the bonds that hold new virus
particles to the outside of an infected cell. Once the enzyme breaks
these bonds, this sets free new viruses that can infect other cells and
spread infection. Neuraminidase inhibitors block the enzyme's activity
and prevent new virus particles from being released, thereby limiting
the spread of the infection. Antiviral
medicines should be considered for people 1 year and older who want to
be treated or avoid the flu and its complications. Health care
providers should also consider those at high risk of flu complications.
These medicines are an important step in fighting flu, but do not
replace the best defense— the flu vaccine. People allergic to these drugs or their ingredients should not take them. Zanamivir
generally is not recommended for people with chronic respiratory
diseases such as asthma or chronic obstructive pulmonary disease
(COPD). In clinical studies, some patients with mild or moderate asthma
or COPD had bronchospasm (wheezing) after taking zanamivir. If you have
an underlying respiratory disease and have been prescribed zanamivir,
your health care provider should instruct you to have a fast-acting
inhaled bronchodilator available for use when taking zanamivir. The dosage of oseltamivir may need to be adjusted if you have any type of kidney disease. None
of these drugs is recommended for routine use during pregnancy or
nursing. These drugs have not been evaluated in pregnant women, and
researchers do not know the effects these drugs could have on the
unborn child. In the laboratory and in limited clinical studies,
there have been no reported interactions of the neuraminidase
inhibitors with other drugs. For complete safety information about these drugs, talk with your pharmacist or health care provider. Studies
have shown that all four drugs can reduce the duration of flu symptoms
by 1 day if taken within 2 days of the onset of the illness. There is
no information about how effective these drugs are if treatment is
started more than 2 days after the onset of flu symptoms. When
taken as directed to prevent the flu, oseltamivir can significantly
reduce your chance of getting the disease if there is a flu outbreak in
your family or community.
The main way to keep from getting flu is to get a yearly flu
vaccine. You can get the vaccine at your health care provider's office
or a local clinic, and in many communities at workplaces, supermarkets,
and drugstores. You must get the vaccine every year because it changes. Scientists make a different vaccine every year because the strains
of flu viruses change from year to year. Nine to 10 months before the
flu season begins, they prepare a new vaccine made from inactivated
(killed) flu viruses. Because the viruses have been killed, they cannot
cause infection. The vaccine preparation is based on the strains of the
flu viruses that are in circulation at the time. It includes those A
and B viruses expected to circulate the following winter. More information about A and B viruses. Sometimes, an unpredicted new strain may appear after the vaccine
has been made and distributed. Because of this, even if you do get the
flu vaccine, you still may get infected. If you do get infected,
however, the disease will usually be milder because the vaccine will
still give you some protection. Until recently, you could get the flu vaccine only as an injection
(shot). In 2003, however, the Food and Drug Administration (FDA)
approved a nasal spray flu vaccine called FluMist that you can get from
your health care provider. The FDA approved it for use in healthy
people aged 2 to 49 years. Children or teenagers who regularly take aspirin or products containing aspirin also should not take FluMist. Your immune system takes time to respond to the flu vaccine.
Therefore, you should get vaccinated 6 to 8 weeks before flu season
begins in November to prevent getting infected or to reduce the
severity of flu if you do get it. Because the flu season usually lasts
until March, however, it's not too late to get the vaccine after the
season has begun. The vaccine itself cannot cause the flu, but you
could be exposed to the virus by someone else and become infected soon
after you are vaccinated. You should be aware that the flu shot can cause side effects. The
most common side effect in children and adults is soreness at the site
of the vaccination. Other side effects, especially in children who
previously have not been exposed to the flu virus, include fever,
tiredness, and sore muscles. These side effects may begin 6 to 12 hours
after vaccination and may last for up to 2 days. Some people may opt for FluMist, the nasal-spray vaccine. Some side effects include runny nose, headache, cough, and fever. Viruses for producing the vaccine are grown in chicken eggs and then
killed with a chemical so that they can no longer cause an infection.
The flu vaccine may contain some egg protein, which can cause an
allergic reaction. Therefore, if you are allergic to eggs or have ever
had a serious allergic reaction to the flu vaccine, the Centers for
Disease Control and Prevention (CDC) recommends that you consult with
your health care provider before getting vaccinated. If you are in any of the following groups or live in a household
with someone who is, CDC recommends that you get the flu vaccine. Health care providers and volunteers should get the flu vaccine if they work with people in any of the above groups. Although the flu vaccine is the best way to prevent getting the flu,
four antiviral medicines that will help prevent flu infection are also
available by prescription. Two of these antivirals, amantadine and
rimantadine, are no longer recommended because of documented influenza
A resistance to them. Tamiflu may be used by adults and children who are 1 year of age and
older. For people 5 years of age and older, Relenza is used to prevent
the flu. Your health care provider can help you decide which medicine is best
for you. You should discuss the flu vaccine and medicines with your
health care provider before the flu season begins.Symptoms
Complications
Flu Complications In Children And Teenagers
Other Complications Of The Flu That Can Affect Children
Diagnosis
Treatment
Flu Drugs
How Do Flu Drugs Work?
Who Should Consider Using These Drugs?
How Much Do These Drugs Help?
Prevention
Flu Vaccine
You Should Not Use FluMist If
Possible Side Effects
Vaccine Recommendations
Medicine for Prevention
Influenza, or flu, is a respiratory infection caused by several flu
viruses. Flu viruses are classified as types A, B, and C; type A has a
number of subtypes. The flu is not the same as the common cold, nor is it related to what is commonly called the “stomach flu.” Seasonal flu is the term used to refer to the flu outbreaks that
occur yearly, mainly in the late fall and winter. It is estimated that
between 5 and 20 percent of Americans come down with the flu every flu
season. Pandemic flu refers to particularly virulent strains of flu that
spread rapidly from person to person to create a world-wide epidemic
(pandemic). In nature, the flu virus also occurs in wild aquatic birds such as
ducks and shore birds. It does not normally spread from birds to
humans. However, pigs can be infected by bird influenza (as well as by
the form of influenza that affects humans) and can pass on the flu to
humans. In 1997, it was discovered that a virulent bird influenza had
skipped the pig step and had infected humans directly, causing a number
of deaths in Asia. These instances of bird flu in humans have raised concerns that if
this type of flu could at some point be transmitted between people, a
new pandemic would occur. Thus, the term bird flu or avian flu is
currently being used to refer to a possible pandemic flu. The flu, like the common cold, is a respiratory infection caused by
viruses. But the flu differs in several ways from the common cold. For
example, people with colds rarely get fevers or headaches or suffer
from the extreme exhaustion that flu viruses cause. The most familiar
aspect of the flu is the way it can "knock you off your feet" as it
sweeps through entire communities. The Centers for Disease Control and Prevention (CDC) estimates that
5 to 20 percent of Americans come down with the flu during each flu
season, which typically lasts from November to March. Children are two
to three times more likely than adults to get sick with the flu, and
children frequently spread the virus to others. Although most people
recover from the illness, CDC estimates that in the United States more
than 200,000 people are hospitalized and about 36,000 people die from
the flu and its complications every year. Seasonal flu outbreaks usually begin suddenly and occur mainly in
the late fall and winter. The disease spreads through communities,
creating an epidemic. During the epidemic, the number of cases peaks in
about 3 weeks and subsides after another 3 or 4 weeks. Half of the
population of a community may be affected. Because schools are an
excellent place for flu viruses to attack and spread, families with
school-age children have more infections than other families, with an
average of one-third of the family members infected each year. Besides the rapid start of the outbreaks and the large numbers of
people affected, the flu is an important disease because it can cause
serious complications. Most people who get the flu get better within a
week (although they may have a lingering cough and tire easily for a
while longer). For elderly people, newborn babies, and people with
certain chronic illnesses, however, the flu and its complications can
be life-threatening. A flu virus is roughly round, but it can also be elongated or
irregularly shaped. Inside are eight segments of single-strand RNA
containing the genetic instructions for making new copies of the virus.
Flu's most striking feature is a layer of spikes projecting from its
surface. There are two different types of spikes: one is the protein
hemagglutinin (HA), which allows the virus to "stick" to a cell and
initiate infection, the other is a protein called neuraminidase (NA),
which enables newly formed viruses to exit the host cell.
Influenza A virus. Credit: CDCSeasonal Flu
Pandemic Flu
Avian (Bird) Flu
Overview of the Flu
Seasonal Flu Outbreaks
Importance of Flu
Flu Virus Characteristics
Influenza viruses are classified as type A, B, or C based upon their protein composition. Type A viruses are found in many kinds of animals, including ducks, chickens, pigs, and whales, and also humans. The type B virus widely circulates in humans. Type C has been found in humans, pigs, and dogs and causes mild respiratory infections, but does not spark epidemics.
Type A influenza is the most frightening of the three. It is believed responsible for the global outbreaks of 1918, 1957, and 1968. Type A viruses are subdivided into groups based on two surface proteins, HA and NA. Scientists have characterized 16 HA subtypes and 9 NA subtypes.
Type A subtypes are classified by a naming system that includes the place the strain was first found, a lab identification number, the year of discovery, and, in parentheses, the type of HA and NA it possesses, for example, A/Hong Kong/156/97 (H5N1). If the virus infects non-humans, the host species is included before the geographical site, as in A/Chicken/Hong Kong/G9/97 (H9N2). There are no type B or C subtypes.
In nature, the flu virus is found in wild aquatic birds such as ducks and shore birds. It has persisted in these birds for millions of years and does not typically harm them. But the frequently mutating flu viruses can readily jump the species barrier from wild birds to domesticated ducks and then to chickens. From there, the next stop in the infectious chain is often pigs.
Pigs can be infected by both bird (avian) influenza and the form of influenza that infects humans. In a setting such as a farm where chickens, humans, and pigs live in close proximity, pigs act as an influenza virus mixing bowl. If a pig is infected with avian and human flu simultaneously, the two types of virus may exchange genes. Such a "reassorted" flu virus can sometimes spread from pigs to people.
Depending on the precise assortment of bird-type flu proteins that make it into the human population, the flu may be more or less severe.
In 1997, for the first time, scientists found that bird influenza skipped the pig step and infected humans directly. Alarmed health officials feared a worldwide epidemic (a pandemic). But, fortunately, the virus could not pass between people and thus did not spark an epidemic. Scientists speculate that chickens may now also have the receptor used by human-type viruses.
Influenza virus is one of the most changeable of viruses. These genetic changes may be small and continuous or large and abrupt.
Small, continuous changes happen in type A and type B influenza as the virus makes copies of itself. The process is called antigenic drift. The drifting is frequent enough to make the new strain of virus often unrecognizable to the human immune system. For this reason, a new flu vaccine must be produced each year to combat that year's prevalent strains.
Type A influenza also undergoes infrequent and sudden changes, called antigenic shift. Antigenic shift occurs when two different flu strains infect the same cell and exchange genetic material. The novel assortment of HA or NA proteins in a shifted virus creates a new influenza A subtype. Because people have little or no immunity to such a new subtype, their appearance tends to coincide with a very severe flu epidemic or pandemic.
Bookmarks The following information, which has been distilled by the casebook author from this and other websites is particularly relevant to this casebook.| Web Page | Notes | Concepts |
|---|---|---|
| U.S. Center for Disease Control and Prevention | (Influenza) | |
| Basics about Flu (Influenza) from causes to complications. General publications, Spanish language information, and other fact sheets to order or to download and print. | (Swine influenza) | |
| U.S. Department of Health and Human Services. Outstanding site in multiple languages with video, RSS updates and Twitter | (Influenza) | |
