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