Systematic Veterinary Virology

TRANSMISSION

• FMDV spread by following methods:
• Direct or indirect contact with infected animals.
• Through aerosol from infected animals
• Feeding contaminated garbage (meat, milk, blood, glands, bones, cheese, etc.)
• Contact with contaminated objects (hands, footwear, clothing).
• Artificial insemination.
• Contaminated biological such as hormones
• Through animate objects (A person in contact with infected animals can have sufficient FMDV in his or her respiratory tract for 24 hours to serve as a source of infection for susceptible animals)
• As airborne, especially in temperate zones for a distance of (up to 60 km overland and 300 km by sea.
• In an outbreak of FMD, the roles of the three primary hosts in transmission are as follows:
  • Sheep act as maintenance hosts,
  • Pigs act as amplifiers,
  • Cattle act as indicators.
• When sheep or goats become infected with FMDV, the disease may not be diagnosed for a long time because signs and lesions are very mild. But during this time, the animals will be producing infectious aerosols, contaminating fomites, and spreading the virus by contact.
• Foot-and-mouth disease in pigs spreads very rapidly, for they produce 30 to 100 times more virus in aerosols than sheep or cattle. (An infected pig can produce a hundred million infectious doses per day).
• When cattle are infected with FMDV, signs and lesions usually develop more rapidly and are more severe than in pigs, sheep, or goats. If cattle, sheep, and pigs are exposed together, cattle will usually get sick first.
• Some animals particulary recovered cattle can be carriers of FMDV. Most ruminant species harbour the virus in their pharyngeal tissues for a long period.