INFLUENZA VIRUS

INTRODUCTION  Family orthomyxoviridea  Genus influenza virus  Genome RNA  Types A, B, C

HISTORY  In 1918, J.S. Koen, a veterinarian, observed a disease in pigs  In 1928, N. McBryde attempted to transmit influenza from pig to pig  Robert 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 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 RBCs 16 HA antigenic subtypes from H1 –H16 80 % 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

NEURAMINIDASE It is shaped like a square There are 9 subtypes of NA:N1 through N9 The top consists of 4 identical proteins forming a roughly spherical shape Its 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

o These 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