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NADIS Parasite Forecast - October

PF Capture

At the start of August the weather was unsettled with low pressure in charge, and wet in the south. It was generally changeable during the first fortnight, and windy at times in the first week. It was often more settled in the second half, although the 20th had a notably vigorous depression for the time of year which brought strong winds to many parts of England. Frequent southerly winds brought a spell of high temperatures over much of England, especially East Anglia and the south-east, which peaked on the 23rd when a few spots recorded 34 °C.  (

October Parasite Forecast/Update

The most recent version of this monthly parasite forecast may be accessed at


This month's parasite forecast focuses upon liver fluke for three reasons:

  • 2016/17 is likely to present a high liver fluke disease risk in western regions of the UK
  • 2015/16 was a high risk year for liver fluke in these same regions leading to pasture contamination this spring/summer
  • Surveys and field data reveal that the majority of farmers do not know which is the best fluke treatment to use against specific stages of the developing parasite.


Chronic liver fluke (right) in a ewe causing death in January 2016, normal healthy liver left.  This situation arose because the farmer had used albendazole in October 2015 and no other flukicide drugs. Seek advice when unsure of fluke risk and which drugs to use.

Section of the liver featured above (normal liver, top; fluke-infected liver, bottom).


Industry representatives have urged farmers to consult their veterinary surgeon and SQP to develop their knowledge of liver fluke to ensure flock profitability and sheep welfare.

  • Liver fluke disease was a major disease problem in western regions of the UK over the winter months of 2015/16.
  • If wet conditions prevail throughout September this will result in a 'high risk' of liver fluke disease in western regions of Scotland, Wales, and northwest England.
  • A more accurate prediction of fluke risk will be provided during October once September weather conditions have been analysed but this may come too late for some farms with a history of liver fluke disease.
  • It is likely that prophylactic treatment with triclabendazole during September/early October will be necessary on those farms in Scotland, northwest England, and Wales where there is a history of liver fluke disease.
  • Central and eastern regions of England are forecast to be at 'low risk'.

Signs of liver fluke disease

  • Sheep with acute fluke infestation may simply be found dead without prior signs of illness therefore it is important to have all sudden deaths investigated to allow immediate implementation of preventive measures.
  • Postmortem examination is essential to establish a diagnosis of acute fluke.
  • Less severe clinical signs include reduced grazing, rapid weight loss, weakness, abdominal pain, anaemia, and slow to gather.


Less severe clinical signs of subacute liver fluke diseases include rapid weight loss, poor fleece, and weakness.


Anaemia (pale mucous membranes) caused by liver fluke disease


  • Triclabendazole is the only flukicide effective against very young immature flukes.
  • Evasion strategies should be adopted wherever possible by not grazing potentially contaminated, poorly-drained areas.
  • Where flukicide treatment is necessary, sheep should be moved from these infested pastures.
  • Stratergies to monitor the effectiveness of fluke treatments should be developed in conjunction with your veterinary surgeon.
  • The coproantigen ELISA test can be used to detect the presence of fluke two to three weeks after dosing which make indicate triclabendazole resistance, and farmers should contact their veterinary practitioner for further advice where such drug resistance is suspected.
  • Faecal egg count reduction tests are unreliable in acute fluke infections as eggs don't start to appear in faeces until 10-12 weeks post-infection.
  • Later fluke treatments (November/December onwards) could include either closantel or nitroxynil especially when triclabendazole resistance is suspected/proven on the farm.
  • Flocks with no previous evidence of fluke disease must maintain their farm's biosecurity especially with respect to purchased sheep but also cattle.


Evasion strategies for liver fluke should also be adopted wherever possible by not grazing potentially contaminated, poorly drained areas.

Parasitic Gastroenteritis (PGE)

  • Clinical PGE is likely as larval challenge remains high on contaminated pastures.
  • Use of Group 4 (monepantel) or Group 5 (derquantel and abamectin) anthelmintics at this time of year can be considered in flocks to prolong the efficacy of the more commonly used Group 1-3 anthelmintics, and are essential in those flocks with confirmed triple-resistance (all anthelmintics in Groups 1-3).  These POM-V products should only be used after detailed consultation with your veterinary surgeon (see August 2016 parasite forecast for further discussion).


Consult your SQP or veterinary surgeon should scouring occur after movement onto 'safe pasture'.

Anthelmintic treatments pre-tupping

  • Anthelmintic treatment of all breeding females pre-tupping is rarely necessary
  • Dosing all ewes pre-tupping may select for anthelmintic resistant strains.
  • In general terms, anthelmintic treatment should be targeted at leaner ewes, gimmers, or those sheep with dags.  These sheep should form no more than 5% of the group.
  • Rams are often neglected at this time and a faecal worm egg count will decide whether a pre-tupping anthelmintic treatment is necessary.


Poor fleece, lower body condition compared to peers and widespread dags two months after weaning. Anthelmintic treatment should be targeted at such leaner ewes. Investigate potential cause(s) if a high percentage of sheep (>5%) are in such poor condition despite good grazing.


  • Cattle may also be at risk from liver fluke in western regions of the UK this autumn
  • The choice of treatment in cattle will be influenced by risk of infection; meat/milk withdrawal periods; risks posed by other parasites; and ease of administration.
  • A bulk milk tank ELISA to monitor herd exposure to fluke and efficacy of control programmes is available.
  • Do not administer combined closantel and ivermectin preparations immediately on housing in October or November because closantel is not effective against early immature liver flukes.
  • Cattle exposed to liver fluke infection should be dosed with closantel or nitroxynil at least six weeks after housing to ensure that all fluke stages in the liver are susceptible to these drugs.
  • Very few products can be used in dairy cattle, and veterinary advice should be sought for treatments at drying off and only considered if there is evidence of fluke infection in the herd.
  • Observe meat and milk withholding periods, so it is important to check labelling on individual products.


  • Growing cattle housed after their first or second season at pasture should be treated with either a Group 1 or 3 anthelmintic at housing, which are effective against inhibited larvae.
  • Pour-on Group 3 preparations have the added advantage they are also effective against both sucking and chewing lice.



Severe louse infestations reflect poorly on farm management, cause reduced growth and raise animal welfare concerns

Local farm conditions may vary so consult your veterinary surgeon. Parasite control should be part of your veterinary health plan.