1. Microbiology of Influenza

2. Introduction
The influenza virus is the only member of the orthomyoxviruses family.
There are three types, A, B and C.

3. Influenza 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

4. Glycoprotein Spikes
Glycoprotein 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.

5. Glycoprotein Spikes Hemagglutin
Endocytosis is triggered when it binds to pulmonary epithelial cells.
Image courtesy of
Neuraminidase
Hydrolyzes mucous in the lungs so virus can attach to the cell surface.
Image courtesy of

6. Influenza A, B & C Influenza A Influenza B Influenza C
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

7. Antigenic 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

8. Antigenic Variations Antigenic Shift Antigenic Drift
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
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

9. Influenza 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