Listeriosis
An adult ewe with a right sided head tilt
Case history - Observations
- 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