INFLUENZA VIRUS

INTRODUCTION

Family orthomyxoviridea Genus influenza virus

Genome RNA

Types A, B, C

HISTORYIn 1918, J.S. Koen, a veterinarian, observed

a disease in pigsIn 1928, N. McBryde attempted to transmit

influenza from pig to pigRobert Shope inoculated unfiltered material The term “influenza” was coined by an

Italian in the mid-1700’s to connote a disease resulting from miasma (bad air).

Wilson Smith, Christopher Andrews, and Patrick Laidrow first identified the virus that causes human influenza

STRUCTURE OF INFLUENZA Roughly Spherical

Virion diameter ranges from 80-120 nanometers

Enveloped virus,the outer layer is lipid membrane taken from host in which virus multiplies

Inserted on membrane are SPIKES

These spikes are the glycoproteins known as Hemagglutinin (HA)

Neuraminidase (NA)

These are the proteins that determine the type of the influenza virus(A,B, and C) and the subtypes(e.g. A/H1N1)

Embedded on the lipid membrane is the M2(ion channel),which is the target of the antiviral adamantanes

Beneath the lipid membrane is a viral protein called M1(matrix protein).This protein which form a shell gives strength and rigidity to the lipid envelope

Interior of the virion are the viral RNAs ,genetic material which code for proteins

NEP,another protein is also present

Its genome is not single piece of nucleic acid but consists of pieces of segmented negative sense RNAs

Influenza A and B 8 segments of ssRNA Influenza C

7 segments of ssRNA with negative polarity

HEMAGGLUTININ Named because of its ability to

agglutinate or clump the host’s RBCs16 HA antigenic subtypes from H1 –H1680% spikes are hemagglutinin It is a trimeric,combination of three

identical proteins,bound together to form a cylindrical shape

It binds virus to target cell and enter viral genome in the target cell

Hemaggulutinin

VIRUS HOST INTERACTION

NEURAMINIDASEIt is shaped like a squareThere are 9 subtypes of NA:N1 through

N9The top consists of 4 identical proteins

forming a roughly spherical shapeIts is involved in the release of progeny

virus from infected cells by cleaving sugars that bind the mature viral particles

It cleaves terminal sialic acid residues from host membrane bound glycoprotein and glycolipids

NEURAMINIDASE

oThese proteins are the antigen to which antibodies can be raised These proteins are the targets of antiviral drugs

The virus is constantly changing its structure