Influenza

Influenza A

  • 8 RNA segments
  • Human animal hosts
    • Avian, equine, porcine (🐦, 🐴, 🐷)
  • Combo of
    • 17 HA (Haemagglutinin) - binding
    • 9 NA (Neuraminidase) - mobility though resp tract
  • Human pathogens-
    • H1N1
    • H2N2
    • H3N2
  • Genetic shift = pandemics
  • Genetic drift = epidemic

Influenza B

  • Antigenic DRIFT NOT shift
    • Pandemic (local epidemic)
  • No animal reservoir ❌
  • LOW mortality 😃

Influenza C

  • Cold like illness 🤒
  • 7 RNA
  • No NA
  • NO epidemics

ILI

  • Sudden onset
  • High temp (>38C)
  • One of:
    • Headache
    • Myalgia 💪🏼
    • Sore throat, cough 💦 with no other infection

Clinical manifestation

  • Incubation = 1/5 days
  • SUDDEN onset
  • Seen as
    • Headache
    • Myalgia 💪🏼
    • Cough 💦
    • Fever 🤒
    • Anorexia 🖊
  • Fever peaks 1/2 days = 41 C

H1N1

  • Some GI symptoms

Complications

URTI

  • Otitis media 👂🏽
  • Sinusitis 👃🏼

LRTI

  • Asthma exacerbation 🌬 (COPD)
  • Croup, bronchiolitis 🐶
  • 1° viral pneumonia (rare)
  • 2° bacterial pneumonia
  • Cardiac involvement ❤
  • Reye's syndrome (brain & liver swelling)

At risk

  • Elderly, residential units 👵🏼
  • Children 🚸
  • Chronic:
    • Resp disease
    • HD ❤
    • Diabetes
    • Immunosuppression
    • Haematology
    • Renal failure

Lab Dx

MDCK cells for virus isolation

Direct IF 🔦

NP aspirant (NOT throat swab)

Shell vial Assay 🐚

Live virus needed

PCR

dropped image link
Apple green = positive

Antigenic variation

EM

Antigenic Drift 🏎

  • Point mutation genes encoding H & N surface proteins
  • Human influenza
    • 8 mutations/year
  • Uquine influenza
    • 3
  • Avian influenza
    • Unchanged last 50 years

Antigenic Shift ↔

  • Protein coat change 👕
    • Re-assortment of fragmented genome during replication 🔄
      • Genetic reassortment
  • LESS frequent
    • pandemic strain (no immunity)

Epidemic

  • Influenza A or B
  • Abruptly
    • 2/3 weeks (peak) - 6/8 weeks (lasts)
  • Attack rate
    • 10/20% overall
    • 40/50% in certain population
    • Fatality high (in chronic cx)
      • DM, COPD

Pandemic 🗺

  • New subtypes due to acquisition of genes from animal/ avian viruses 🐕🐦
  • Influenza A
  • Attack rate
    • 50% (+/- 2nd/3rd wave)
    • 80% in selected population
  • Worldwide

Transmission of avian Influenza to human

  • Bird faeces 🐦💩
  • Direct infection rarely occurs

LPAI (low pathogenic avian influenza)

  • H7N7
  • H7N9

HPAI (high pathogenic avian influenza)

  • H7N7
  • H5N1

Controlling spread

Survey

  • Particularly potential pandemic strains
    • Seasonal surveillance via sentinel system 📆🤖

Vaccination 💉

  • Trivalent 3⃣
    • H3N2 & H1N1 (2 A)
    • Seasonal flu (B)

Depends on

  • Antigenic similarity between vaccine and circulating virus
  • Age & immunocompetence (patient)

Protection

  • Re-vaccination pre-season
  • 2 weeks for immunity to develop

Type

  • 1) Inactivated
    • Disrupted virus particles
    • Virus grown in hen's eggs 🥚
      • Issue allergy to eggs
  • 2) Live attenutaed
    • Given intra-nasally 👃🏽
    • Sub-clinical infection 🌡

Anti-viral agents

  • Resistant mutants present thus selective use needed

Matrix protein inhibitors ❎

  • Amantidine & Rimantidine 👨🏻
    • Influenza tx
    • Neuro S/E common

Neuraminidase Inhibitors ❌

  • ZanaMivir & OseltaMivir (TAMIFLU) 👆🏼
    • For influenza A & B