Pathogenicity

PATHOGENECITY

Symptoms

  • Four syndromes
    • Subclinical
      • Infections are the most common form of infection.
      • Usually outbreak occurs when fed with poor quality, high pH silage, particularly during cold weather.
    • Neonatal infections
      • Characterised as visceral infections with a septicemia.
      • Often gastroenteritis and bilateral meningitis.
      • Deaths are frequent in neonatal animals.
    • Listerial abortion
      • It is a sporadic condition in cattle and sheep.
      • It occurs after 4-8 months pregnancy. Retained placenta is common.
    • Neural Listeriosis (circling disease):
      • The incubation period ranges from 14 to 40 days.
      • The disease is more common in winter or early spring.
      • The clinical presentation of meningoencephalitis in adult ruminants may begin with signs of depression and confusion.
      • The ears droop; animal holds its head to one side.
      • Protrusion of the tongue and salivation are common and twitching or paralysis of the facial and throat muscles may occur.
      • When the animal moves, it tends to be in a single direction, giving rise to the common name of circling disease.
      • In the terminal stages, the animal may fall and will be unable to rise.
    • In poultry, there are signs of
      • Torticolis
      • Weakness
      • Incoordination of legs and
      • Sudden death in young birds
  • The disease is usually fatal in sheep, pigs and horses.

Lesions

  • Micro-abscess in the brain stem, usually unilateral, together with perivascular cuffing is very characteristic of listeriosis.
  • The lesions are most common in the mid brain, pons and medulla oblongata.
  • In addition to this there will be generalized septicaemia, focal necrosis of the liver and spleen will be seen.
Last modified: Monday, 4 June 2012, 4:49 AM