Microbiology of Influenza

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

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

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.

Glycoprotein Spikes Hemagglutin 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 & 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

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

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

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