Post on 31-Dec-2015
description
Influenza Viruses
• Classified into types A, B, and C– Types A and B cause
significant disease worldwide– Types B and C limited to
humans– Type A viruses
• More virulent• Wild waterfowl reservoir• Affect many species
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Photo: Cynthia Goldsmith, CDC
Influenza A Viruses
Categorized by subtype • Classified according to two
surface proteins– Hemagglutinin (HA) – 16 known
subtypes• Site of attachment to host cells• Antibody to HA is protective
– Neuraminidase (NA) – 9 known subtypes
• Helps release virions from cells• Antibody to NA can help modify
disease severity
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This image is in the public domain in the United States
Hemagglutinin
H1
H2
H3
H4
H5
H6
H7
H8
H9H10
H11
H12
H13
H14
H15
H16
N1
N2
N3
N4
N5
N6
N7
N8
N9
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Influenza A HA and NA Subtypes
Other Animals
Other Animals
Other Animals
Other Animals
Other Animals
Other Animals
Seasonal Influenza Transmission Routes
• Influenza is an acute respiratory disease– Signs and symptoms reflect respiratory
route– Fever, cough, headache, muscle aches– Sometimes lower respiratory
• Transmission of influenza viruses– Person-to-person through droplets from
coughing or sneezing– Transmission from objects (fomites) possible– Infectious 1 day before and up to 7 days
after becoming sick
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U.S. Centers for Disease Control and Prevention
Seasonal Influenza Communicability
• Viral shedding can begin 1 day before symptom onset
• Peak shedding first 3 days of illness
• Subsides usually by 5-7th day in adults
• Infants, children and the immunosuppressed may shed virus longer
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U.S. Centers for Disease Control and Prevention
Human Influenza Clinical Diagnosis
• Clinical symptoms non-specific– Symptoms overlap with
many pathogens– Couple with laboratory data
to verify diagnosis – Even during peak seasonal
influenza activity, only about 30% specimens tested for influenza are positive in the United States
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U.S. Centers for Disease Control and Prevention
Human Influenza Complications
– Sinus and ear infections– Viral and bacterial pneumonia– Myocarditis and Pericarditis– Myositis – Encephalopathy and
encephalitis – Febrile seizures– Worsening of underlying
chronic conditions– Sepsis-like syndrome in
infants9
U.S. Centers for Disease Control and Prevention
April 2009 Swine-Origin Influenza A (H1N1) Virus (S-OIV)
• The strain currently circulating is a novel Influenza A(H1N1)
• It is thought to be composed of avian, human, and swine components from various continents
• This strain is most likely a new subtype of A/H1N1 not previously seen in swine or humans
• The strains isolated in the US and Mexico appear to be identical
General S-OIV Information
• There are four main influenza type A virus subtypes that have been isolated in pigs: H1N1, H1N2, H3N2, and H3N1
• Swine-origin influenza viruses have high attack rates and low death rates in pigs
• Swine-origin influenza viruses do NOT typically infect humans – until this outbreak, there had been 12 cases in the US since December 2005, with no deaths
Food Safety
• You cannot contract swine-origin influenza from eating pork or pork products.
• Eating properly handled and cooked pork products is safe. Cooking pork to an internal temperature of 160°F kills the swine-origin influenza virus as it does other bacteria and viruses.
Transmission of S-OIV
• Human transmission of swine-origin influenza and seasonal influenza viruses is thought to occur in the same way
• Transmission can occur via:– Contact with secretions from persons infected with
swine influenza virus– Contact with infected pigs or environments (surfaces,
objects) contaminated with the virus
Human infection with S-OIV
• Symptoms may include:– Fever, cough, headache, muscle aches (similar to
seasonal influenza)– Some people reported diarrhea, nausea and vomiting
• Symptom onset begins 1-5 days after exposure
• Infected individuals can spread the virus as long as they are symptomatic (or at least 7 days following illness onset)
Case Definitions• Suspect Case: a person with acute febrile respiratory illness with
onset – within 7 days of close contact with a person who is a confirmed case of
S-OIV infection, or – within 7 days of travel to community either within the United States or
internationally where there are one or more confirmed cases of S-OIV infection, or
– resides in a community where there are one or more confirmed cases of S-OIV infection.
• Probable Case: a person with an acute febrile respiratory illness who is positive for influenza A, but negative for H1 and H3 by influenza RT-PCR
• Confirmed Case: a person with an acute febrile respiratory illness with laboratory confirmed S-OIV infection at CDC by one or more of the following tests: – real-time RT-PCR – viral culture
Treatment of S-OIV
• The CDC recommends Oseltamivir (Tamiflu) and Zanamivir (Relenza) for treatment– Oseltamivir is approved to treat and prevent infection in
people at least 1 year old– Zanamivir is approved to treat infection in people at
least 7 years old, and to prevent infection in people at least 5 years old
• Antiviral drugs are most effective within 2 days of symptom onset
• There is currently NO vaccine available for swine influenza but it is anticipated that one will be developed in the next few months
Requirements for an Influenza Pandemic Virus
• A new influenza A subtype virus emerges that can infect humans
AND
• Causes serious illness
AND
• Spreads easily from human-to-human in a sustained manner
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