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NADIS Parasite Forecast - October

Use of meteorological data to predict the prevalence of parasitic diseases

PF Capture

August was an often unsettled month with some large daily rainfall totals in some areas. Ex-Hurricane 'Bertha' passed over the UK on 10th to 11th bringing some unseasonably windy and wet weather, before moving into the North Sea and maintaining a cool and showery regime. The second half of the month saw some notably cool days and nights with some early ground frosts, and remained unsettled resulting in a cool and wet month overall.

The provisional UK mean temperature was 13.9 °C, 1.0 °C below the 1981-2010 long-term average. This was the coolest August for the UK since 1993, ending a sequence of eight warmer than average months. Rainfall was above average, particularly across northern Scotland which had its wettest August in a series from 1910. The UK overall received 156% of average rainfall and this was equal-seventh wettest in the series. It was a slightly sunnier than average month in the north and west with 107% of average sunshine hours for the UK overall. (

October Parasite Forecast/Update

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


Weather conditions during early summer (May to July) were drier than normal, and this low rainfall in most areas contributed to an early forecast of 'low to normal liver fluke disease risk'. While August was a wet month in most areas, much of September has been dry and warm.  Taking the worst case scenario and affording September and October maximum scores on the MORECs scale, there is a high risk of liver fluke disease only in Scotland with a moderate risk in all other areas except for the SE of England where there is only a low risk.

  • It should be remembered that the fluke forecast covers very large geographical areas and farmers should consult their own veterinary surgeon regarding recommendations for their own flock.
  • However, in general, early flukicide treatments to prevent acute/sub-acute fluke infestations using triclabendazole may only be necessary in Scotland.
  • The moderate risk for the western half of England and Wales could mean that fluke treatments are delayed until later in the autumn.
  • The effectiveness of fluke treatments should be monitored by your veterinary surgeon.
  • Strategies using alternative flukicide products, such as closantel, should be included later in the year in high risk areas to overcome potential triclabendazole resistance problems.
  • Flocks with no previous evidence of fluke disease must maintain their farm's biosecurity especially with respect to purchased sheep but also cattle.

Fig 1

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


Continue quarantine treatments of all purchased stock

  • Quarantine arrangements are still essential to reduce the risk of introducing anthelmintic-resistant worms with purchased sheep.
  • Current best practice involves sequential full dose treatments with either monepantel (Zolvix) or derquantel/abamectin (Startect) and moxidectin 1% injection upon arrival on farm.
  • Confine sheep for 24-48 hours, then turn out onto pasture recently grazed by sheep.
  • Maintain purchased stock in separate groups and monitor closely for disease for at least 30 days before mixing with home flock.



  • Clinical PGE is likely to become a problem on contaminated grazing in many areas as the larval challenge increases because farmers are not sending lambs to market at present due to low prices leading to over-stocked pastures.
  • Use of Group 4 (monepantel) or Group 5 (derquantel and abamectin) anthelmintics at this time of year could 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).  The use of such products should only be used after detailed consultation with your veterinary surgeon.

Fig 2

  • 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 and is discouraged in the SCOPS guidelines.
  • In general terms, anthelmintic treatment should be targeted at leaner ewes, gimmers, or those sheep with dags.
  • Rams are often neglected at this time and a faecal worm egg count will decide whether a pre-tupping anthelmintic treatment is necessary.


Fig 3

Anthelmintic treatment should be targeted at leaner ewes, gimmers, or those with dags. Investigate cause if a high percentage of sheep are in poor condition.


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


Cattle exposed to liver fluke infection should be dosed after housing; the interval between housing and treatment will depend on the efficacy of the product used against immature fluke stages. For example if closantel is used, it must be given at least six weeks after housing to ensure that all fluke stages in the liver are susceptible to this drug.


Fig 4

Pour-on Group 3 preparations have the added advantage over other anthelmintic options in that they are effective also against both sucking and chewing lice.



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