H1N1: “Swine Flu”

Why you should care…• Every year between 5 and 20% of the

population gets the flu.• The CDC estimates that the flu kills

36,000 people annually.• On average over 200,000 people are

hospitalized for flu related infections.• The Flu season is from November to

March

Who gets it?• Animals and humans

• Pigs, birds, and humans are the preferred hosts, and each have their own strain (type) of influenza that has unique characteristics from other strains.

Who gets it?• Since pigs, birds, and humans are the preferred

hosts, interactions among these species allow host-adapted strains (virus changes to live in or benefit from unique characteristics of cell of its different hosts) that can be identified by serotype (like H1N1).

Types of Influenza• There are two main types:

– Influenza A– Influenza B

• Each type (A & B) has subtypes• Flu viruses are always changing to

different subtypes

Serotype of the strain is the “H” and “N” of its name, “H1N1”

• HA = hemagglutinin (16 types)– Allows the virus to bind to host cells.– Hijacks host receptor to gain entry.

• NA = neuraminidase (9 types)– Allows the virus to escape host cells so it

can spread to other cells.• M2 = protein important for virus

replication.• Different combinations of H and N

determine which species are susceptible and the morbidity of the infection.

(Binds to receptors on host cell)

HA

(Helps initiate infection)

NA

H1N1: Let’s Take a Look(Binds to receptors on host cell)

HA

(Helps initiate infection)

NA

How does the Flu Virus Change?– The Flu Virus is ALWAYS changing– Antigenic Drift – small changes that happen

continually over time•Happens often•LESS DRAMATIC CHANGE

– Antigenic Shift – abrupt, major change in the influenza A virus, resulting in a new subtype•Happens less often•MUCH MORE DRAMATIC CHANGE

Antigenic drift

“A” immune “B” susceptible “A” susceptible

Antigenic shift

Mixed infection Reassortment New strain of virus

The Evolution of Influenza Viruses

Why do we get the flu over and over?Influenza viruses can change in

several ways:• It is an RNA virus so it

doesn’t have the same “spell check” mechanism that DNA viruses do. Influenza can mutate all by itself through errors in replication without correction.

• Influenza also switches genes with other strains that code for surface proteins.

– This is common during “mixed infections” where a cell is infected with more than one strain.

Why do we get the flu over and over?• The immune system

does not recognize the new, host-adapted strains.

• Pig cells are like mixing pots. They are susceptible to influenza usually found in pigs, humans, and birds! – Their cells have

receptors for human and bird viruses as well as pig viruses

Pandemic = PANIC?• This is a new strain of influenza (H1N1)

and most people are going to be susceptible; HOWEVER, it is not a strain with a high mortality.

• We are not all going to die.• The WHO scaled up this virus to a phase 5

pandemic based on distribution and human-human transmission, not based on lethality.

Prevention and Preventing Spread• Get vaccinated!• Cover your nose and mouth when you

cough or sneeze.• Wash your hands often especially after

coughing or sneezing.• Avoid close contact with sick people.

Questions?Avoid close contact with sick pigs.