Influenza Overview

  • Influenza Characteristics

    • Known as the flu, caused by virus strains in the Orthomyxoviridae family.

    • Key components include Hemagglutinin (HA), Neuraminidase (NA), and RNA genome.

Structure of Influenza Virus

  • Neuraminidase (NA)

    • An enzyme that helps the virus to escape from the infected cells by cleaving sialic acid residues.

  • Hemagglutinin (HA)

    • A glycoprotein that facilitates the binding of the virus to the host cell by attaching to sialic acid on the cell surface.

  • Envelope

    • A lipid bilayer that surrounds the virus, derived from the host cell membrane.

  • RNA Genome

    • Composed of eight segments of RNA, coding for various proteins essential for viral replication and infection.

HA and NA Functions

  • HA Binding Site

    • Region on the Hemagglutinin where sialic acid binds, critical for the virus's ability to infect host cells.

Historical Overview of Influenza Strains

  • Key Influenza Strains and Their Impact

    • 1889 – H2N2

    • 1900 – H3N8 and H3N2

    • 1918 – H1N1 (Spanish Flu), caused up to 50 million deaths globally; related to avian flu genes.

    • 1957 – H2N2 (Asian Flu), resulted in about 70,000 deaths in the U.S.; first found in China.

    • 1968 – H3N2 (Hong Kong Flu), led to approximately 34,000 deaths in the U.S.; features genes from human and avian influenza.

    • 1977 – H1N1 (Russian Flu

    • 2000 – H5N1 (Avian Flu), H1N2, H3N2

    • 2009 – H1N1 (Swine Flu), ended up claiming at least 14,000 lives globally; vaccines were developed within 3 months of the first reported cases.

Clinical Focus 13.1: Pandemics Overview

  • Influenza A Pandemics in the Last Century

    • 1918-19: H1N1 caused significant mortality with up to 50 million deaths worldwide.

    • 1957-58: H2N2, approximately 70,000 deaths in the U.S.; combination of human and avian genes.

    • 1968-69: H3N2, resulted in around 34,000 deaths in the U.S.; also a mix of human and avian genetic material.

    • 2009-10: H1N1 again, with a death toll of at least 14,000 worldwide; vaccine available rapidly.

Virological Composition

  • Figure Components (Env, Gag, Pol)

    • Envelope Proteins

    • Surface Glycoprotein SU (gp120)

      • Part of the envelope that aids in binding to host cells.

    • Transmembrane Glycoprotein TM (gp41)

      • Facilitates fusion of viral and host cell membranes.

    • GAG (Core Proteins)

    • Membrane Associated Protein MA (p17)

      • Structural component contributing to the virus's stability.

    • Capsid CA (p24)

      • Forms the shell of the virus protecting its RNA.

    • POL (Polymerase and Related Proteins)

    • Protease PR (p9)

      • Enzyme responsible for cleaving proteins during the viral life cycle.

    • Polymerase RT & RNAse H (p66)

      • Replicates RNA genome and processes RNA of the virus.

    • Integrase IN (p32)

      • Integrates viral genetic material into the host genome.