Microbiology of InfluenzaMicrobiology of Influenza

IntroductionIntroduction

The influenza virus is the only member of the orthomyoxviruses family.

There are three types, A, B and C.

Influenza VirusInfluenza Virus The influenza virus

contains ssRNA in its core

This is surrounded by a matrix protein membrane

A lipid bilayer envelopes the virus

The outer layer is studded with prominent glycoprotein spikes

Courtesy of http://micro.magnet.fsu.edu/cells/viruses/influenzavirus.html

Glycoprotein SpikesGlycoprotein SpikesGlycoprotein spikes help the virus

attach to a cell.There are two types of glycoprotein

spikes.– Hemagglutin (HA)– Neuraminidase (NA)

The number of HA and NA on the surface determines the name of the specific virus, ex. H5N1, avian flu.

Glycoprotein SpikesGlycoprotein SpikesHemagglutin

Endocytosis is triggered when it binds to pulmonary epithelial cells.

Image courtesy of http://upload.wikimedia.org/wikipedia/en/a/a1/Hemagglutinin_molecule.png

Neuraminidase Hydrolyzes mucous in the

lungs so virus can attach to the cell surface.

Image courtesy of http://en.wikipedia.org/wiki/Image:Neuraminidase_Ribbon_Diagram.jpg

Influenza A, B & CInfluenza A, B & CInfluenza A

Eight –ssRNA molecules

Infects humans and animals such as pigs and birds

Can cause serious infections

Influenza B Eight –ssRNA

molecules Infects only

humans Can cause

serious infections

Influenza C Seven –ssRNA

molecules Infects only

humans Can cause only

minor infections usually in a family or classroom

Antigenic VariationsAntigenic Variations

The influenza virus mutates easily and can change from year to year.

This is why you need a flu shot every year to prevent the flu.

Influenza can mutate in two different ways.– Antigenic drift– Antigenic shift

Antigenic VariationsAntigenic Variations

Antigenic Drift Minor changes in HA and

NA Occurs in influenza A and

B Antibodies are not

effective against new mutation

Causes a minor epidemic about every two years

Antigenic Shift Major changes in HA and

NA Occurs only in influenza A Two different influenza

viruses enter cell and combine causing a new influenza strain

Causes major epidemic about every 10 years

Influenza MicrobiologyInfluenza Microbiology

The stomach flu is usually caused by other viruses or bacteria, not influenza.

No matter what flu shots come out, some people still get the flu.

The virus is constantly changing and mutating making it hard for the body to combat what would seem like a simple RNA