Atypical acute parasitic gastroenteritis weanlings

RVL Surveillance Bulletin 4

October 2018

Atypical acute parasitic gastroenteritis (worm infestation) in weanlings, Autumn 2018

The Regional Veterinary Laboratory (RVL) service has observed a pattern of unusual cases of gut worm infestation in weanlings in autumn 2018. These cases have generally been characterised by:

  • Acute disease (signs of illness have come on suddenly)
  • Low or negative worm egg counts shortly before death or after death in some cases on which necropsy (detailed veterinary post mortem examination) was carried out
  • A history of intensive dosing in other cases on which necropsy was carried out
  • Geographical concentration in the Midwest region
  • Severe damage to the gut visible to the naked eye, but no visible worms. Microscopic examination of the gut tissues revealed large numbers of prepatent (immature) worms.


This syndrome should not be confused with “summer scour syndrome” where recognised gut pathogens, including worms and other parasites, are not found.

Cases of the atypical worm infestation syndrome have been found in at least seven different herds in counties Limerick, Clare and Tipperary, during the months of September, October and November. Both dairy and beef animals have been affected.

It is possible that the unusual syndrome is associated with the long dry spell during the summer of 2018 whereby many of the infective larvae were trapped within the dried faecal pats. Mass translation of these infective larvae onto pasture in a short period of time following the arrival of rain may give rise to sudden infestations in individual animals with a large number of larvae. This could also explain the sudden onset of severe signs and the absence or scarcity of worm eggs in dung samples.

Thanks to Limerick RVL for the information provided. Further information on the work of the RVL service is available here:


 Atypical Gastroenteritis

 Inflammatory changes & thickening in the abomasal wall of a weanling with atypical gastroenteritis

 Photo:  Denise Murphy, Athlone RVL

Species: Bovine
3:43 PM on Mon, 19 November