Foot and Mouth Disease

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VIRUSES
PICORNAVIRUSES



Morphology

  • Very small (25nm) RNA virus
  • 12 capsomeres (1 per vertex)
  • 5 subunits per capsomere
  • 1 molecule of virus protein (VP) per subunit
  • 4 virus proteins (VP1-VP4)
  • VP1 is the attachment protein

Antigenicity

  • FMDV was the first animal virus in which serotypes were isolated
  • To date, there are (important in bold):
    • Oise (O)
    • Allemagne (A)
    • C (also German)
    • South African Territories (SAT) 1, 2, and 3
    • India (Asia-1)
  • Each serotype has at lease three subtypes
  • Serotype and subtype can be quickly identified by ELISA using guinea pig antisera
  • All isolates are virulent

Hosts

  • Cloven-hoofed animals, EXCLUDING the horse
    • Cattle
    • Sheep
    • Goats
    • Pigs
    • Deer
    • Elephants
    • Wild ruminants: buffalo, kudu, impala, etc

Pathogenesis

  • Primary replication in the upper respiratory tract, tonsils, or upper alimentary tract
  • Aerosol excretion during this incubation period
  • Viremia
  • Virus targets stratum spinosum of stratified squamous epithelia and mucus mebranes
  • Secondary vesicles appear after incubation of 2-14 days
  • Appearance of lesions by age:
    • 0-2 days: unruptured vesicles
    • 1-3 days: newly ruptured vesicles with adherent epithelia at margins
    • 3-7 days: ruptured vesicles, loss of epithelia, no marked fibrous margin
    • 7-10+ days: open lesions with marked fibrous margin
  • Prevalence of lesions by species:
    • Pigs:
      • Lesion at coronary band means infection is usually less than a week old
      • Lesions grow down claw at a rate of 1mm per week
    • Cattle

Epidemiology

Diagnosis

Control