Influenza (the flu)
By
Salwa Hassan Teama
Ain Shams University
Difference Between Cold or FLU
A cold is a milder respiratory illness than the flu. While cold symptoms can
make you feel bad for a few days. Flu symptoms can make you feel quite ill for
a few days to weeks.
Cold symptoms usually begin with a sore throat, which usually goes away after
a day or two. Nasal symptoms, runny nose, and congestion follow, along with a
cough by the fourth and fifth days. Fever is uncommon in adults, but a slight
fever is possible. Children are more likely to have a fever with a cold.
With cold symptoms, your nose teems with watery nasal secretions for the first
few days. Later, these become thicker and darker.
Whether a person has typical seasonal flu or swine flu, the symptoms seem to
be quite similar. Flu symptoms are usually more severe than cold symptoms
and come on quickly. Symptoms of swine flu and seasonal flu include sore
throat, fever, headache, muscle aches and soreness, congestion, and cough.
Swine flu in particular is also associated with vomiting and diarrhea.
Influenza (the flu)
Influenza
(the flu) is a contagious respiratory illness caused by
influenza viruses. It can cause mild to severe illness, and at times
can lead to death. The best way to prevent seasonal flu is by getting
a seasonal flu vaccination each year.
•In virus classification influenza viruses are RNA viruses that make
up three of the five genera of the family Orthomyxoviridae.
Influenzavirus A
Influenzavirus B
Influenzavirus C
Influenza A virus
•The type A viruses are the most virulent human pathogens among the three
influenza types and cause the most severe disease. Type A flu or influenza A
viruses are capable of infecting people as well as animals.
•Wild aquatic birds are the natural hosts for a large variety of influenza A.
•The influenza A virus can be subdivided into different serotypes based on the
antibody response to these viruses. The serotypes that have been confirmed in
humans, ordered by the number of known human pandemic deaths, are:
•H1N1, which caused Spanish flu in 1918, and the 2009 flu pandemic
•H2N2, which caused Asian Flu in 1957
•H3N2, which caused Hong Kong Flu in 1968
•H5N1, a current pandemic threat
•H7N7, which has unusual zoonotic potential
•H1N2, endemic in humans and pigs
•H9N2
•H7N2
•H7N3
•H10N7
Influenza B virus
Influenza B almost exclusively infects humans and is less common than
influenza A. This type of influenza mutates at a rate 2–3 times lower than
type A. This reduced rate of antigenic change, combined with its limited
host range ensures that pandemics of influenza B do not occur.
Influenza virus C
Influenza C virus, which infects humans, dogs and pigs, sometimes
causing both severe illness and local epidemics. However, influenza C is
less common than the other types and usually only causes mild disease
in children.
Structure
•Influenzaviruses A, B and C are very similar in overall
structure. The virus particle is 80–120 nanometres in diameter
and usually roughly spherical, although filamentous forms can
occur. These filamentous forms are more common in influenza
C, which can form cordlike structures up to 500 micrometres
long on the surfaces of infected cells.
The viral particles of all influenza Viruses are
similar in composition. These are made of a
viral envelope containing two main types of
glycoproteins, wrapped around a central
core.
The central core contains the viral RNA
genome and other viral proteins that
package and protect this RNA.
RNA tends to be single stranded but in
special cases it is double. Unusually for a
virus, its genome is not a single piece of
nucleic acid; instead, it contains seven or
eight pieces of segmented negative-sense
RNA, each piece of RNA contains either one
or two genes. For example, the influenza A
genome contains 11 genes on eight pieces of
RNA, encoding for 11 proteins:
hemagglutinin (HA), neuraminidase (NA),
nucleoprotein (NP), M1, M2, NS1, NS2(NEP),
PA, PB1, PB1-F2 and PB2
Hemagglutinin & Neuraminidase
Hemagglutinin (HA) and neuraminidase (NA) are
the two large glycoproteins on the outside of the
viral particles. HA is a lectin that mediates
binding of the virus to target cells and entry of
the viral genome into the target cell, while NA is
involved in the release of progeny virus from
infected cells, by cleaving sugars that bind the
mature viral particles.
Thus, these proteins are targets for antiviral
drugs. Furthermore, they are antigens to which
antibodies can be raised.
•Influenza A viruses are classified into subtypes based on antibody
responses to HA and NA. These different types of HA and NA form the basis of
the H and N distinctions in, for example, H5N1. There are 16 H and 9 N
subtypes known, but only H 1, 2 and 3, and N 1 and 2 are commonly found in
humans.
•The most prevalent human flu viruses are H1N1 and H3N2. All of the human
versions of H1N1 and H3N2 can easily transmitted from person to person
because the H1 and H3 proteins recognize human cell receptors, making it
easy for them to split into healthy cells.
Seasonal Flu
Seasonal flu is the term used to refer to the flu outbreaks that occur yearly,
mainly in the late fall and winter.
Pandemic Flu
Pandemic flu refers to particularly virulent strains of flu that spread rapidly from
person to person to create a world-wide epidemic (pandemic).
Avian (Bird) Flu
The flu virus 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.
Complications of Flu
•Most flu symptoms gradually improve over two to five days, but it's not uncommon to
feel run down for a week or more. A common complication of the flu is pneumonia,
particularly in the young, elderly, or people with lung or heart problems. If you notice
shortness of breath, you should let your doctor know. Another common sign of
pneumonia is fever that comes back after having been gone for a day or two.
• Ear infections,
•Sinus infections,
•Dehydration, and
•Worsening of chronic medical conditions, such as congestive heart failure, asthma, or
diabetes.
Influenza Pandemic
Influenza spreads around the world in seasonal epidemics, resulting in the
deaths of hundreds of thousands annually — millions in pandemic years. Three
influenza pandemics occurred in the 20th century and killed tens of millions of
people, with each of these pandemics being caused by the appearance of a
new strain of the virus in humans. Often, these new strains appear when an
existing flu virus spreads to humans from other animal species, or when an
existing human strain picks up new genes from a virus that usually infects birds
or pigs. An avian strain named H5N1 raised the concern of a new influenza
pandemic, after it emerged in Asia in the 1990s, but it has not evolved to a form
that spreads easily between people. In April 2009 a novel flu strain evolved that
combined genes from human, pig, and bird flu, initially dubbed "swine flu" and
also known as influenza A/H1N1, emerged in Mexico, the United States, and
several other nations. The World Health Organization officially declared the
outbreak to be a "pandemic" on June 11, 2009 . The WHO's declaration of a
pandemic level 6 was an indication of spread, not severity.
Bird Flu
•Fifteen subtypes of influenza virus are known to infect birds, thus providing an
extensive reservoir of influenza viruses potentially circulating in bird populations. To
date, all outbreaks of the highly pathogenic form have been caused by influenza A
viruses of subtypes H5 and H7.
•The strain of avian flu known as H5N1 has been behind most recent outbreaks of
deadly avian flu and has also been responsible for the recent human deaths reported in
asia, but there are three prominent subtypes of avian influenza virus and among the
three subtypes, influenza AH5,AH7 and AH9, there are several strains with varying
degrees of strength.
Low pathogenicity (LPAI) - usually only causing mild
respiratory disease in domestic poultry .
High pathogenicity (HPAI) - the more virulent type formerly
known as fowl plague which often results in up to a 100%
flock mortality.
Antigenic “Shift”
This reassortment process, known as antigenic “shift”, results in a
novel subtype different from both parent viruses. As populations will have
no immunity to the new subtype, and as no existing vaccines can confer
protection, antigenic shift has historically resulted in highly lethal
pandemics..
Conditions favorable for the emergence of antigenic shift have long been
thought to involve humans living in close proximity to domestic poultry and
pigs. Because pigs are susceptible to infection with both avian and
mammalian viruses, including human strains, they can serve as a “mixing
vessel” for the scrambling of genetic material from human and avian viruses,
resulting in the emergence of a novel subtype.
Infection Control
Preventing Seasonal Flu: Get Vaccinated
The single best way to prevent seasonal flu is to get a seasonal flu
vaccination each year. There are two types of flu vaccines:
•The "flu shot" : an inactivated vaccine (containing killed virus) that is given
with a needle. The seasonal flu shot is approved for use in people 6 months of
age and older, including healthy people and people with chronic medical
conditions.
•The nasal-spray flu vaccine : a vaccine made with live, weakened flu viruses
that do not cause the flu (sometimes called LAIV for "Live Attenuated
Influenza Vaccine"). LAIV is approved for use in healthy* people 2-49 years of
age who are not pregnant.
About two weeks after vaccination, antibodies develop that protect against
influenza virus infection. Flu vaccines will not protect against flu-like illnesses
caused by non-influenza viruses.
A seasonal flu vaccine will not protect you against the new 2009 H1N1 flu. A
vaccine against the new H1N1 flu is being produced.
•Vaccinations have been produced to help
fight the spread of influenza A, but because
there are so many strains of the virus,
vaccinations are not always effective or
reliable.
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Vaccine safety
•Side effects are expected to be similar to those observed with seasonal
influenza vaccines. Common side effects include local reactions at the injection
site (soreness, swelling, redness) and possibly some systemic reactions (fever,
headache, muscle or joint aches). In almost all vaccine recipients, these
symptoms are mild, self-limited and last 1-2 days.
However, even very large clinical trials will not be able to identify
possible rare events that can occur when pandemic vaccines are
administered to many millions of people. Further testing of safety and
effectiveness will need to take place after administration of the vaccine.
www.who.int/csr/disease/swineflu
What happened during the last swine flu pandemic in 1976?
•The 1976 Swine Flu Vaccine caused Guillain-Barré Syndrome; a crippling
paralysis that can be fatal if not treated quickly.
•Media now reporting that there was an unproven link to GBS, BUT the acting
head of the CDC's Immunization Safety Office, Dr. John Iskander said in Feb.
2008 "A proven association between the 1976-1977 swine influenza vaccine and
Guillain-Barré syndrome.
http://www.wepapers.com/Papers/69348/Swine_Flu_The_virus_and_the_mass_vaccination_campaign.ppt, Are
the vaccines safe? What you absolutely must know before you take the swine flu vaccine (or any other
vaccine).
Treatment
•Treatment with oseltamivir (trade name Tamiflu®) or zanamivir (trade name
Relenza®) is recommended for all people with suspected or confirmed
influenza who require hospitalization.
Who is prioritized for treatment with influenza antiviral drugs?
Most people ill with influenza will recover without complications.
Some people are at highest risk of influenza-related complications and are prioritized for
treatment with influenza antiviral drugs this season. They include:
•People with more severe illness, such as those hospitalized with suspected or
confirmed influenza
•People with suspected or confirmed influenza who are at higher risk for complications
•Children younger than 2 years old
•Adults 65 years and older
•Pregnant women
•People with certain chronic medical or immunosuppressive conditions
•People younger than 19 years of age who are receiving long-term aspirin therapy
References & Update
•http://www.who.int/csr/disease/avian_influenza/en
•http://www.cdc.gov/flu/about/disease/
•http://www.wepapers.com/Papers/69348/Swine_Flu_The_virus_and_th
e_mass_vaccination_campaign.ppt, Are the vaccines safe?
What you absolutely must know before you take the swine flu vaccine
(or any other vaccine).
•www.SwineFluShots.us