Bovine spongiform encephalopathy

BOVINE SPONGIFORM ENCEPHALOPATHY


Synonym -  Mad cow disease

Definition

  • It is a non-inflammatory, degenerative disease of CNS in cattle, which is invariably fatal caused by prion protein (PrP)

Incidence

  • First reported in 1986 in British dairy herd, later in Ireland, in cattle exported from England to Oman, Italy, Denmark, Germany, Canada. Reported in native cattle of France, Switzerland and Portugal

Etiology

  • Caused by a prion protein (PrP)
  • Normal prion protein does not cause the disease but the abnormal form produces neurologic disease

Incubation period

  • Unusually long about 4-5years

Transmission

  • Feeding of meat / bone meal /meat meal supplements to cattle

Pathogenesis

  • Normal prion protein (PrP) in neurons of CNS (α – helix iso form)
  • Transformed (change in shape or form) to abnormal form (PrPsc) (β – pleated sheet)
  • Prion protein becomes resistant to digestion by proteases
  • Accumulation of PrPsc in neural tissue causes prion diseases
  • Following oral infection long incubation period before infection
  • At this time infective agent is present in low concentration in lymphoid tissue in tonsils, suprapharyngeal lymphnode and lymphoid tissue of intestine
  • Spread to other lymph nodes and spleen
  • Continues to replicate in extra intestinal and intestinal lymphnodes for even a year
  • Reaches CNS -the target organ

Clinical signs

  • Long incubation period (4-5years)
  • Apprehension, anxiety, fear
  • Abnormalities in posture and gait
  • Extreme sensitivity to sound and touch
  • Loss of weight
  • Repeated falling
  • Recumbency
  • Clinical signs last for 2 weeks to 6 months
  • Because of the peculiar and uncontrollable behavior of the affected cow, the disease in called as “Mad – cow disease”
  • Mostly females are affected

Microscopical lesions

  • Vacuolation in cytoplasm of neurons of the neuropil (spongiosis)
  • Gliosis
  • Ballooned neurons with narrow rim of cytoplasm
  • Scrapie – associated fibrils under electron microscopy of brain tissue

Diagnosis

  • Based on clinical signs
  • Pathology of brain of affected animals
  • Use of antibodies against prion protein
Last modified: Monday, 19 March 2012, 6:33 AM