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NADIS Parasite Forecast - November

Use of meteorological data to predict the prevalence of parasitic diseases

PF Capture

September was dominated by high pressure, bringing plenty of fine and settled early-autumn weather, with only a few short interruptions. This meant that rainfall was limited in most regions, and temperatures were generally above average, though with no exceptional warmth on any particular days.

The provisional UK mean temperature was 13.9 °C, 1.3 °C above the 1981-2010 long-term average. This made it the equal-fourth warmest September for the UK in a series since 1910, although not as warm as 2006. It was also only the fifth time that the UK mean temperature for September has equalled or exceeded that for August. Rainfall was well below average in most places, with less than 20% of the long-term average over large swathes of the country, and an overall UK figure of just 23% of average. This was provisionally the driest September in a series since 1910, though only slightly drier than 1959. It was also the driest calendar month for the UK since August 1995. Sunshine was very close to normal overall, though it was sunnier relative to average on the western side than further east. (

November 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 very wet month in most areas of the UK, September was the second driest since records began.

Even taking the worst case scenario for October with a maximum score on the MORECs scale, there are no predicted high risk regions for liver fluke disease this year and only a moderate risk covering Scotland; all other areas of the UK are predicted to have a low risk.

  • In general, early flukicide treatments to prevent acute/subacute fluke infestations in moderate risk areas using triclabendazole should now be followed by closantel or nitroxynil 6-8 weeks later.
  • The low risk for the western half of England and Wales could mean that fluke treatments can be delayed until later in the autumn when closantel or nitroxynil could be used in areas where previously triclabendazole was necessary.
  • While the liver fluke risk is predicted to be low to moderate, preventing pasture contamination by strategic treatments remains an integral component to control liver fluke disease next year.



  • 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.
  • The dry weather during September may have prevented nematode larvae from either leaving the faecal mass, or migrating onto the herbage. Contaminated pastures will become infective after wet weather when a flush of infective larvae will appear on the pasture and this may be dangerous for grazing stock.
  • Outbreaks of trichostrongylosis are often seen in late autumn/winter in store and replacement lambs, and sometimes gimmers.  Heavy infestations can cause black foetid diarrhoea with associated rapid weight loss.
  • As the weather becomes colder, most acquired Haemonchus larvae will inhibit in the abomasal wall of the host sheep resuming development again in the spring if left untreated.  Treatment will be indicated in those flocks with a history of haemonchosis; note that arrested larvae will not produce eggs.


Fig 1

Over-stocked pastures and wet weather during October may lead to late season problems with parasitic gastroenteritis.


Fig 2

Trichostrongylosis is often seen in late autumn/winter in store and replacement lambs.

  • Consult your veterinary surgeon regarding the possible use of Group 4 (monepantel) or Group 5 (derquantel and abamectin) anthelmintics at this time of year to prolong the efficacy of the more commonly used Group 1-3 anthelmintics.
  • Anthelmintics belonging to Groups 4 and 5 are essential in those flocks with confirmed triple-resistance (all anthelmintics in Groups 1-3).
  • Use of Groups 4 and 5 anthelmintics could also be considered when moving fattening lambs onto catch crops where the refugia concept is less important.


Fig 3

Consult your veterinary surgeon about using Groups 4 and 5 anthelmintics before moving fattening lambs onto catch crops.

Anthelmintic treatments around tupping time

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

Fig 4

Anthelmintic treatment should be targeted at leaner ewes and those sheep with dags.


Fig 5

A pooled faecal worm egg count will decide whether your rams require a pre-tupping anthelmintic treatment.


  • Outbreaks of lungworm may occur after prolonged dry weather when sudden heavy rain, especially thunderstorms, releases infective larvae that have been locked up in faecal pats.
  • Growing cattle housed after their first or second season at pasture should be treated with either a Group 1 or 3 anthelmintic at housing.


  • Despite the low fluke risk this year in many regions, 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.
  • When using combination products such as closantel and ivermectin, the timing of treatment must relate to closantel (six weeks after housing) as too early treatment after housing will be ineffective against early stage flukes.

Fig 6

Severe liver fluke infestation.  Treatment with closantel must be delayed until at least six weeks after housing.


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