Disease of the Day - Influenza

3 types of Influenza

Type A

Type B

Type C

Influenza A

Broken into subtypes: based on glycoproteins present

• hemagglutinin (H)

• neuraminidase (N)

Subtypes broken into strains

Cause of major pandemics

Influenza B

Infects humans only (geographic epidemics)

Broken into strains

Influenza C

No epidemics - mild disease

Infects humans and pigs

What animals can have influenza A

Ducks

Chickens

Pigs

Whales

Horses

Cats

Humans

Orthomyxovirus - RNA Virus

Replication Strategy of 8 pieces of RNA for type A/B only;

Only 7 pieces for type C

RNA virus means high mutation rates (no proofreading of polymerase since -ssRNA)

Evolves quickly

Influenza A

16 H subtypes and 9 N subtypes (available)

Many combinations of proteins

Most found in birds - makes birds natural reservoir

Pigs can be infected with both human and avian influenza viruses making pigs a “mixing pot”

Antigenic DRIFT

RNA virus mutates in host

Slight resistance in population

Happens all the time

Get new strains (yearly)

Influenza B can only drift

Antigenic SHIFT

Pigs infected with human, bird, and pig virus

Can mix genes

Completely new subtype - so no resistance in population

Only happens occasionally

New Pandemic Possible

Who Antigenic DRIFT affects

Death in the…

• elderly

• immunocompromised

• death due to secondary infections or underlying health conditions

Who Antigenic SHIFT affects

Death in the …

• Healthy adults

• Death due to hemorrhagic edema

History of Influenza

1918 Spanish Flu

• 20-40 million died world-wide

1957 Asian Flu

• 1.5 million died world-wide

1968 Hong Kong Flu

• 1.5 million died world-wide

1997 Avian Flu

• over 200 deaths

Seasonal Influenza

More than one strain circulating at one time

Droplet transmission

Respiratory tract (50,000-500,000 virus/droplet)

Fomite transmission

Nonliving object-spread infection

• Touch nose

• Touch mouth

Severity of Influenza

Each year, the US averages 36,000 deaths from flu-related complications

200,000 people are hospitalized from flu-related causes

Children 5 and under, and adults 65 and older are main targets

Prevention

Seasonal vaccine

Wash hands often

Cover your nose and mouth when coughing or sneezing

Avoid close contact with sick people

Stay home for 24 hours when sick