Foot and Mouth Disease

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