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

Part One

Seasonal Influenza

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

3

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

4

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

5

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

6

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

7

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

8

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

Part Two

Swine-Origin Influenza Virus

(S-OIV)

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

Part Three

Pandemics

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

19

Pandemic Influenza Phases

Resources

• http://PandemicFlu.gov• CDC’s Swine Flu Info Center:

http://www.cdc.gov/swineflu/?s_cid=swineFlu_outbreak_001

• WHO’s Swine Flu Info Center http://www.who.int/csr/disease/swineflu/en/