Foot and Mouth disease

FOOT AND MOUTH DISEASE

Synonym : Aphthous fever,Aftosa,Enzootic apthiae

Definition

  • Acute highly contagious febrile disease of cloven footed animals
  • Formation of vesicles in mouth and feet of cattle,sheep, goat and swine

Etiology 

  • Picorna virus group,
  • GENUS-APHTHOUS VIRUS
  • Serotypes – O, A,C, and South African type SAT1, SAT2, SAT 3  and Asia 1 of which O,A,C and Asia 1 - prevalent in India

Incubation period

  • Few hours to few days
  • Sheep: Incubation period is 3 to 8 days

Susceptibility

  • All cloven footed animals and it is rarely fatal except in very young animals
  • The disease is also seen in elephants and camels

Transmission

  • Ingestion of contaminated materials

Pathogenesis

Vrius is epitheliotropic

  • Virus invades epithelial cells, multiplies resulting in vesicle firmation finally causing focal areas of inflammation
  • Invades lymph and blood results in viremia and reaches epithelium of other mucous membrane, interdigital space, dorsum of tongue, gums etc.producing vesicles
  • Causes myocardial degeneration in young calves

Clinical signs

  • High temperature
  • Vesicles appear on mouth
  • Rupture leaving ulcer - refuses feed and water
  • Vesicles on cleft of feet leading to lameness
  • Also seen in lightly haired parts (Udder and teat)
  • Produces smacking noise or smacking of tongue
  • Drooling of saliva

Gross lesions

  • Vesicles on the mucosa of lips, dorsum of tongue and palate in cattle and also in coronet, udder and teat
  • Lesions also seen – Rumen, reticulum and omasum
  • Haemorrhage and diffuse oedema in mucosa of abomasum and small intestine
  • Death may be due to gastroenteritis and myocardial lesions in young calves -"Tigroid heart"
  • In sheep: Oral lesions appear on the dental pad only

Microscopic lesions

  • Vacuoles appear in the cells of epithelium with eosinophilic cytoplasm and pyknotic nuclei. These small vesicles coalesce to form larger ones and the epithelium gets detached
  • Hyaline degeneration and necrosis of myocardial fibres and also in sketetal muscles - "Tigroid heart appearance"
  • Secondary bacterial infections produces osteomyelitis and suppurative arthritis

Secondary Effects

  • Mastitis
  • Anaemia
  • Disturbances in sexual function
  • Diabetes
  • Over growth of hair
  • Cardiac cicatrices
  • Panting
  • Dyspnoea
  • Delayed growth of young animals

Important sequelae of FMD is infertility and decreased production probably due to endocrine damage especially the thyroid gland

Diagnosis

  • Clinical signs and lesions
  • Complement fixation test
  • Virus isolation and polymerase chain reaction 
Last modified: Saturday, 17 December 2011, 9:54 AM