Looking Like Lots of Listeria Locally- report from the SAC

Looking Like Lots of Listeria Locally- report from the SAC

February brought with it multiple diagnoses of listeriosis in all its forms suggesting there may be a high risk of disease this spring.  Very muddy ground conditions may be to blame in some cases.

The presentations the SAC have seen on separate farms are:

  • Abortion – Has been diagnosed in sheep, beef and dairy cattle with all isolates bar one (L. ivanovii) being L. monocytogenes.  Very occasionally pin point abscesses are seen on the foetal liver.  Abortion can occur from 5 to 12 days after infection.
  •  Encephalomyelitis – usually caused by Listeria bacteria entering areas of damaged oral mucosa, gaining access to the trigeminal nerve, ascending to the brain stem and producing micro-abscesses.  Do not dismiss listeriosis as a differential if the typical signs of unilateral facial paralysis are absent.  Depending on lesion distribution they may not be seen.  The pathogenesis means that 2 to 6 weeks can elapse between infection and the development of clinical signs.  It is difficult to culture listeria from the brain stem so histopathology is often needed to confirm a diagnosis.

As lambing approaches, please consider listeriosis as a differential diagnosis, as well as the common metabolic causes of nervous disease in adult sheep.

  • Abomasitis/enteritis/septicaemia – Clinical signs of scour, pyrexia, dullness and anorexia can be seen within 2 days of infection.

Listeria sp. are ubiquitous environmental bacteria and are also found in the faeces of normal animals.  They will multiply in silage following entry of air and when pH is ≥ 5.5.  Spoiled silage is traditionally blamed for most outbreaks of listeriosis but in cases seen has not always been fed.  The wet winter has left muddy conditions which could increase disease risk through ingestion of soil.

  • Avoid feeding silage that is either obviously spoiled or from punctured bales.  The top layer of the pit and the outer layer of bales are highest risk.
  • Clean away uneaten silage before adding more.
  • Make silage accessible to sheep avoiding trampling by muddy feet.
  • If rolls are fed directly onto the ground change the area where feeding takes place.
  • Check silage analyses for high pH and/or high ash content (>80g/kg DM) indicating large amounts of soil contamination at harvest e.g. cut very low, molehills or wet weather at harvest.

Submitting abortion material or non viable nervous disease cases for PM will help in confirming the diagnosis where necessary.

Related SEV Branch