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Introduction

The influenza virus

Influenza virions are enveloped particles of spherical or elongated shape, measuring 80–120 nm in diameter and containing a segmented, single-stranded RNA genome (see Chapter 2). 12, x RA Lamb, RM Krug. Orthomyxoviridae: the viruses and their replication. DM Knipe, PM Howley, DE Griffin (Eds.) et al. Fields Virology 4th edn. (Lippincott Williams & Wilkins, 2001) (1487 - 1531) 13 x PF Wright, RG Webster. Orthomyxoviruses. DM Knipe, PM Howley, DE Griffin (Eds.) et al. Fields Virology 4th edn. (Lippincott Williams & Wilkins, 2001) (1533 - 1579) The influenza virus belongs to the family of the Orthomyxoviridae. There are three influenza genera, or virus types, within this family: influenza A, B and C. Influenza A viruses have been responsible for the major pandemics of influenza in the last century and are also the causative agents for most of the annual outbreaks of epidemic influenza. Therefore, this book will be limited mostly to a discussion of the characteristics and impact of influenza A viruses.

Figure 1 presents an electron micrograph of the influenza A virus. A characteristic feature of the virus is its outermost layer of spike-like projections. These are the two viral surface glycoproteins, haemagglutinin (HA) and neuraminidase (NA), which are embedded in the lipid membrane of the viral envelope. HA, the major spike protein, is responsible for attachment of the virus to specific receptors on the host cell surface. HA also mediates a fusion reaction between the viral envelope and the cell membrane, through which the viral genome gains access to the interior of the cell (see Chapter 2). Once inside the cell, the viral RNA is replicated and viral proteins are synthesized, leading to the production of many thousands of new virus particles per cell. Ultimately, the cell dies as a result of the infection. In the lungs and airways, this process of cell lysis leads to desquamation of the respiratory epithelium as one aspect of influenza pathogenesis (see Chapter 5).

Figure 1 Negative-stain electron micrograph of influenza A virus. source: Courtesy of Drs Takeshi Noda and Yoshihiro Kawaoka.

f01-01-9780723434337

References in context

  • Figure 1 presents an electron micrograph of the influenza A virus.
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x

Figure 1 Negative-stain electron micrograph of influenza A virus. source: Courtesy of Drs Takeshi Noda and Yoshihiro Kawaoka.

f01-01-9780723434337

References in context

  • Figure 1 presents an electron micrograph of the influenza A virus.
    Go to context

References

Label Authors Title Source Year
12

References in context

  • Influenza virions are enveloped particles of spherical or elongated shape, measuring 80–120 nm in diameter and containing a segmented, single-stranded RNA genome (see Chapter 2).12,13 The influenza virus belongs to the family of the Orthomyxoviridae.
    Go to context

  • There are many different influenza A virus subtypes, differing in the nature of the HA and NA glycoproteins on their surface.12,13 Sixteen HAs and nine NAs have been identified.
    Go to context

RA Lamb, RM Krug. Orthomyxoviridae: the viruses and their replication. DM Knipe, PM Howley, DE Griffin (Eds.) et al. Fields Virology 4th edn. (Lippincott Williams & Wilkins, 2001) (1487 - 1531) 2001
13

References in context

  • Influenza virions are enveloped particles of spherical or elongated shape, measuring 80–120 nm in diameter and containing a segmented, single-stranded RNA genome (see Chapter 2).12,13 The influenza virus belongs to the family of the Orthomyxoviridae.
    Go to context

  • There are many different influenza A virus subtypes, differing in the nature of the HA and NA glycoproteins on their surface.12,13 Sixteen HAs and nine NAs have been identified.
    Go to context

  • Influenza pandemics are the result of so-called antigenic shift of the virus (see Chapter 3).13 This means that a virus with a new HA (and NA) is introduced into the human population.
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  • The current information supports the concept that new pandemic influenza viruses are derived from avian virus reservoirs.13,15–17 Avian influenza viruses may be directly transmitted to humans, which probably occurred in the case of the 1918 Spanish flu virus.18,19 The possibility of direct transmission of an avian influenza virus to humans became evident for the first time during the H5N1 outbreak in Hong Kong in 1997.20,21 In this incident, 18 people were infected with the chicken flu virus, six of whom died.
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  • In addition to the emergence of new human influenza virus subtypes with pandemic potential, established human virus subtypes undergo significant antigenic adaptation, referred to as antigenic drift (see Chapter 3).13 Antigenic drift involves minor changes in the HA, NA and possibly also other viral antigens, that occur due to mutations in the viral genome, resulting in amino acid substitutions in antigenic sites.
    Go to context

PF Wright, RG Webster. Orthomyxoviruses. DM Knipe, PM Howley, DE Griffin (Eds.) et al. Fields Virology 4th edn. (Lippincott Williams & Wilkins, 2001) (1533 - 1579) 2001

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