Seasonal Influenza and Swine-Origin Influenza A (H1N1) Virus

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Seasonal Influenza and Swine-Origin Influenza A
(H1N1) Virus
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Part One

• Seasonal Influenza

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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

Photo Cynthia Goldsmith, CDC
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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

Hemagglutinin
This image is in the public domain in the United
States
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Influenza A HA and NA Subtypes
Other Animals
Other Animals
Other Animals
Other Animals
Other Animals
Other Animals
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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

U.S. Centers for Disease Control and Prevention
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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

U.S. Centers for Disease Control and Prevention
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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

U.S. Centers for Disease Control and Prevention
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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 infants

U.S. Centers for Disease Control and Prevention
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Part Two

• Swine-Origin Influenza Virus
• (S-OIV)

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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

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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

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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 160F kills the swine-origin influenza virus
  as it does other bacteria and viruses.

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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

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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)

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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

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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

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Part Three

• Pandemics

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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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Pandemic Influenza Phases
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Resources

• http//PandemicFlu.gov
• CDCs Swine Flu Info Center
• http//www.cdc.gov/swineflu/?s_cidswineFlu_outbre
  ak_001
• WHOs Swine Flu Info Center http//www.who.int/csr
  /disease/swineflu/en/