Listeriosis

Case history - Observations

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• 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