Listeriosis

An adult ewe with a right sided head tilt

Case history - Observations

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Sheep with listeriosis
  • A homebred cheviot cross ewe
  • Ewe is bright alert and responsive
  • Reduced feed intake
  • General clinical examination was normal
  • It is the only affected individual in the flock

Further investigation

A more detailed neurological was performed which revealed;

  • Right sided head tilt
  • Left sided nystagmus
  • Muscle fasiculations (twitching) on right side of muzzle
  • Stumbling to the right

A head tilt is a common presentation in sheep, the main differentials are;

  • Listeria monocytogenes
  • Vestibular (middle ear) disease
  • Brain abscess
  • Trauma
  • Meningitis
  • Polioencephalomalacia (CCN)
  • Hepatic encephalopathy

Diagnosis

Diagnosis is usually based on clinical signs, age and flock history. Further tests that may contribute to a diagnosis are a cerebrospinal fluid tap (benefit to individual and flock) or a necropsy (benefit to flock). The history and clinical signs in this ewe were highly suggestive of listeriosis and so treatment was initiated with a 5 day course of intramuscular procaine penicillin and a one of injection of dexamethasone. The ewe improved with treatment with a resolution of most of the neurological signs and an improvement in the head position. The ewe also returned to normal appetite.

Disease:

Listeriosis is generally caused by poor quality silage being fed to ewes at an age when their teeth are erupting (18 to 24 months). Silage with a pH >5.0 allows for the multiplication of the bacteria which then enters the body through breaks in the oral mucosa around the growing teeth. Outbreaks typically affect about 2% of stock but can be higher. Clinical disease is often not seen until 10-21 days after silage feeding starts.

Prevention:

  • Discard spoiled silage (or feed to cattle)
  • Clean troughs daily
  • Clear leftover feed
  • Avoid soil contamination of feed and troughs
  • Store silage appropriately
  • Addition of acidifying products to grass silage