Influenza A Virus Subtype H1N1

Influenza A virus subtype H1N1
Influenza A (H1N1) virus is a subtype of influenza virus A and the most common cause of
influenza (flu) in humans. Some strains of H1N1 are endemic in humans and cause a small fraction of all
influenza-like illness and a large fraction of all seasonal influenza.
The new strain was initially described as an apparent reassortment of at least four strains of
influenza A virus subtype H1N1, including one strain endemic in humans, one endemic in birds, and two
endemic in swine.
Reassortment is a process that happens if two different types of influenza virus infect a single
cell and it can produce a new strain of influenza. This is because the virus genome is split between eight
independent pieces of RNA, which allows pieces of RNA from different viruses to mix together and form
a novel type of virus as new virus particles are being assembled.
Influenza virus infection occurs after transfer of respiratory secretions from an infected
individual to a person who is immunologically susceptible. If not neutralized by secretory antibodies, the
virus invades airway and respiratory tract cells. Once within host cells, cellular dysfunction and
degeneration occur, along with viral replication and release of viral progeny. Systemic symptoms result
from inflammatory mediators, similar to other viruses.
Sign & Symptoms:
 Nasopharynx: -Lethargy, Lack of Appetite

-Runny Nose, Sore throat  Gastric:
 Systemic: -Nausea & Vomiting
-Fever  Intestinal:
 Physiological: -Diarrhea
Typical symptoms of influenza begin 2-3 days after exposure to the virus.
 Influenza produces an acute febrile respiratory illness with cough, headache, and myalgia
for 3-4 days, with symptoms that may persist for up to 2 weeks.
Patients may present with sudden onset of the Subsequent respiratory symptoms include the
following: following:
1. High fever 1. Sore throat/pharyngitis

2. Chills 2. Nasal congestion
3. Myalgia (muscle/joint pain) 3. Rhinitis
4. Headache 4. Nonproductive cough
5. Fatigue 5. Conjunctivitis
Vaccines:
The 2009 flu pandemic vaccines are the set of influenza vaccines that have been developed to
protect against the pandemic H1N1/09 virus. These vaccines either contain inactivated (killed) influenza
virus, or weakened live virus that cannot cause influenza. The killed vaccine is injected, while the live
vaccine is given as a nasal spray. Both these types of vaccine are usually produced by growing the virus
in chicken eggs. Around three billion doses will be produced annually, with delivery from November
2009
In studies, the vaccine appears both effective and safe, providing a strong protective immune
response and having similar safety profile to the normal seasonal influenza vaccine. However, about
30% of people already have some immunity to the virus, with the vaccine conferring greatest benefit on
young people, since many older people are already immune through exposure to similar viruses in the
past. The vaccine also provides some cross-protection against the 1918 flu pandemic strain.
Early results (pre-25th December 2009) from an observational cohort of 248,000 individuals in
Scotland have shown the vaccine to be effective at preventing H1N1 influenza (95.0% effectiveness [95%
confidence intervals (CI) 76.0-100.0]) and influenza related hospital admissions (64.7% [95%CI 12.0-
85.8]).
Two types of influenza vaccines are available:
1. TIV (flu shot (injection) of trivalent (three strains; usually A/H1N1, A/H3N2, and B) inactivated
(killed) vaccine) or
2. LAIV (nasal spray (mist) of live attenuated influenza vaccine.)
TIV works by putting into the bloodstream those parts of three strains of flu virus that the body uses
to create antibodies; while LAIV works by inoculating the body with those same three strains, but in a
modified form that cannot cause illness.
LAIV is not recommended for individuals under age 2 or over age 50, but might be comparatively
more effective among children over age 2.
Medication:
GENERIC NAME: oseltamivir
BRAND NAME: Tamiflu
DRUG CLASS AND MECHANISM: Oseltamivir is an oral medication used for treating and preventing the
"flu." It is similar to zanamivir (Relenza). Oseltamivir suppresses and decreases the spread of influenza A
and B viruses, the viruses responsible for the flu. It does this by blocking the action of neuraminidase, an
enzyme produced by the viruses that enables the viruses to spread from infected cells to healthy cells.
By preventing the spread of virus from cell to cell, the symptoms and duration of influenza infection are
reduced. On average, oseltamivir reduces the duration of symptoms by one and a half days if treatment
is started within forty-eight hours of the beginning of symptoms. The FDA approved oseltamivir in
October 1999.
PRESCRIPTION: Yes
PREPARATIONS: Capsules: 30, 45, and 75 mg. Suspension: 12 mg/ml
PRESCRIBED FOR: Oseltamivir is used for the treatment of uncomplicated infections with the influenza
viruses, including H1N1, in adults and children (one year and older) within two days of the beginning of
symptoms. It also is approved for emergency use in children less than 1 year old. Oseltamivir can be
used for preventing the flu in healthy individuals, but it is not a substitute for flu vaccine.
DOSING: Oseltamivir is administered orally.

The recommended dose for treating adults is 75 mg twice daily for five days.
Children are treated with 30-75 mg twice daily depending on body weight.
For the best results, treatment should begin within 2 days of symptom onset. The recommended dose
for preventing flu after close contact with an infected individual is 75 mg daily for 10 days.
People high risk:

 Asthma
 Neurological and neurodevelopmental conditions [including disorders of the brain, spinal cord,
peripheral nerve, and muscle such as cerebral palsy, epilepsy (seizure disorders), stroke,
intellectual disability (mental retardation), moderate to severe developmental delay, muscular
dystrophy, or spinal cord injury].
 Chronic lung disease (such as chronic obstructive pulmonary disease [COPD] and cystic
fibrosis)
 Heart disease (such as congenital heart disease, congestive heart failure and coronary artery
disease)
 Blood disorders (such as sickle cell disease)
 Endocrine disorders (such as diabetes mellitus)
 Kidney disorders
 Liver disorders
 Metabolic disorders (such as inherited metabolic disorders and mitochondrial disorders)
 Weakened immune system due to disease or medication (such as people with HIV or AIDS, or
cancer, or those on chronic steroids)
 People younger than 19 years of age who are receiving long-term aspirin therapy
“Emergency warning signs” that should signal anyone to seek medical care
urgently:
In children:
 Fast breathing or trouble breathing

 Bluish skin color
 Not drinking enough fluids
 Not waking up or not interacting
 Being so irritable that the child does not want to be held
 Flu-like symptoms improve but then return with fever and worse cough
 Fever with a rash
In adults:
 Difficulty breathing or shortness of breath

 Pain or pressure in the chest or abdomen
 Sudden dizziness
 Confusion
 Severe or persistent vomiting
 Flu-like symptoms that improve but then return with fever and worse cough.

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Influenza A virus subtype H1N1

Sign & Symptoms:

 Nasopharynx: -Lethargy, Lack of Appetite

1. High fever 1. Sore throat/pharyngitis

Two types of influenza vaccines are available:

DOSING: Oseltamivir is administered orally.

People high risk:

 Fast breathing or trouble breathing

 Difficulty breathing or shortness of breath

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