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Editorial Information

Professor Mike Taylor BVMS PhD MRCVS DipEVPC DipECSRHM CBiol MRSB

Published 2017

Parasite Forecast - December 2017

17-12 Capture

October started changeable and was dominated by a warm moist south-westerly, with some higher than average temperatures at times, ending up colder by the end of the month. The UK mean temperature was 11.3 °C, with mean maximum temperatures generally 1 to 2°C above average.  It was a drier than average except in western Scotland, Cumbria and north Lancashire, with below average rainfall amounts in southern and eastern areas.


December Parasite Forecast/Update


Liver Fluke Forecast

  • The summer has been one of the wettest on record with higher than average rainfall during the months of May through to October in many parts of GB. Based on cumulative wetness scores, the NADIS fluke forecast is predicting a "high-risk" of fluke infection in North, West and central Scotland, West Wales and Cornwall this autumn; with "medium-risk" in Eastern Scotland, and parts of North and South West England.
  • Most of Central and Eastern regions of England are forecast to be at "low-risk".
  • More localised and detailed fluke-risk information will be available through veterinary practices participating in the new NADIS parasite control initiative.




  • If a second triclabendazole (TCBZ) treatment was required in the higher, acute fluke-risk regions of the country, the next fluke treatment can probably be delayed until January.
  • Where TCBZ- resistance has been confirmed, or is suspected, then consider the use of either closantel or nitroxynil, which are active on later immature (> 6-7week-old) and adult fluke.
  • Chronic liver disease in sheep, due to the presence of adult fluke, peaks in the late winter/early spring.
  • Affected sheep may show a progressive loss of condition, weakness, lowered appetite, emaciation, a brittle open fleece, the development of anaemia characterised by pale mucous membranes, and submandibular oedema ("bottle jaw").
  • Albendazole and oxyclozanide are effective from 10-14 weeks post infestation and can be used when treatment is recommended to remove adult flukes only.
  • Subsequent spring treatments will remove any surviving adult flukes and prevent pasture contamination by fluke eggs reducing the risk of disease later in the year.
  • Farmers in lower fluke-risk regions of the country should consult their veterinary surgeon about fluke control measures.
  • If sheep have not been treated, then faecal samples from around 10 animals will identify patent fluke infection acquired during the autumn and indicate the need to treat the flock.

Parasitic gastroenteritis (PGE)

  • Outbreaks of trichostrongylosis in store and replacement lambs, and even gimmers, are a risk during mild, wet weather in November and December.
  • Continue to monitor worm egg counts on pooled faecal samples where there is a risk of disease.
  • Heavy infestations cause black foetid diarrhoea (black scour) and rapid weight loss.

17-12 PFF2

Trichostrongylosis in store and replacement lambs is a risk if mild wet weather continues through November.

Scab and Lice

  • Sheep scab is typically encountered during the autumn/winter months from September to April.
  • The symptoms of both sheep scab and lice can be similar and so diagnosis is important before deciding on treatment.
  • For scab diagnosis, tests available include examining skin scrapings from suspect sheep or an antibody test on blood samples.
  • Sheep scab, caused by the presence of psoroptic mites (Psoroptes ovis), can be very debilitating with significant loss of condition, secondary infections and eventually deaths if not treated.
  • Remember also that sheep scab is notifiable in Scotland.
  • Infestation leads to severe pruritus, wool loss, restlessness, biting and scratching of infested areas, weight loss, reduced weight gain and in some cases, death.
  • The fleece is wet, sticky, yellow, and frequently contaminated with dirt from the hind feet.
  • Typically, after eight weeks' infestation, or so, the hair loss on the flanks may extend to 20 cm diameter surrounded by an area of inflammation and serum exudation. The skin is often thrown into thickened corrugations.

17-12 PFF3

Early sheep scab - rubbing causing breakage of wool over the chest wall.

17-12 PFF4

Advanced sheep scab -there is extensive fleece loss over the chest which is wet, sticky and yellow at the edges due to serum leaking from the skin.
  • Lice infestations are commonly mistaken for sheep scab and vice versa.
  • Like sheep scab, louse populations are highest in sheep during late winter with spread occurring by close contact with other sheep.
  • Infestations of chewing lice are widespread in most sheep flocks. Sucking lice are not a problem in the UK.
  • Louse burdens are most severe in lean/emaciated sheep, are highly visible, and often highlight poor stock management.
  • The welfare implications of heavy louse infestations must not be forgotten.

Scab and Lice Treatments

  • Sheep scab can be controlled by administration of an injectable macrocyclic lactone (ML). Treatment requires either a single, or repeat injection 7-10 days apart, depending of the product and active ingredient.
  • Because of the growing concern over selection of ML-resistance in roundworms and scab mites, it is important to ensure scab treatments are given correctly following current SCOPS guidelines.
  • Louse infestations can be controlled with topical application of high cis cypermethrin or deltamethrin, but these are most effective on shorn sheep.
  • Plunge dipping in diazinon controls both scab and lice infestations.

17-12 PFF5

Louse populations are highest during late winter and may cause disrupted feeding patterns, fleece damage/loss, and self-inflicted trauma.

17-12 PFF6

Poor flock husbandry - heavy louse infestation affecting a hogg in poor condition. Immediate treatment is necessary for welfare reasons.


Liver Fluke

  • Out-wintered cattle in high fluke-risk areas may need dosing in December, but because acute fluke is rare, consideration should be given to using either alternatives to TCBZ.
  • Seek advice and base treatments on local farm conditions and the NADIS fluke forecast.
  • Cattle dosed on housing with these alternative treatments should be tested for the presence of adult fluke, or given a second treatment to ensure all fluke are removed.
  • The interval between housing and testing or re-treatment will depend on the product used. For closantel or nitroxynil the re-treatment interval is 6-7 weeks; and for oxyclozanide or albendazole the interval is 10-12 weeks.
  • Faecal egg counting, serum or bulk milk ELISA testing, and slaughterhouse liver reports, are practical methods of detecting fluke-infected herds.
17-12 PFF7
Slaughterhouse liver reports are a practical means of detecting fluke-infected herds and flocks. The mature flukes are found in the bile ducts but are shown here on the surface of the liver.

Parasitic gastroenteritis (PGE)

  • Autumn-born beef calves should not require anthelmintic treatment at housing.
  • Ostertagia larvae ingested by susceptible yearling stock during the autumn may have arrested their development and overwinter (as early L4) in the abomasal (stomach) wall.
  • These arrested larvae resume their development in late winter/spring and can cause outbreaks of acute scour with subsequent death (type 2 ostertagiosis).
  • Susceptible animals exposed to contaminated pastures during the later grazing season will be at risk from type 2 ostertagiosis unless they have been dosed with an anthelmintic effective against inhibited larvae, at housing, or at least before late winter.
  • Lungworm outbreaks decrease significantly from November onwards. Coughing in unvaccinated susceptible cattle at pasture before housing, or in undosed stock after housing, should be investigated for the presence of lungworm larvae in faecal samples.

17-12 PFF8

Autumn born beef calves should not require anthelmintic treatment at housing


  • Low burdens of lice are very common in the coats of cattle during the winter months and should not necessarily be considered of significance.
  • However, populations can increase rapidly causing intense itching, or anaemia if sucking lice are present.
  • Both chewing and sucking lice are found on cattle in the UK.
  • Heavy louse infestation may be a sign of other underlying conditions and an indicator of ill-thrift.
  • A range of pour-on or spot-on synthetic pyrethroid products (containing alpha-cypermethrin, deltamethrin or permethrin) and macrocyclic lactones are commonly used.
  • Injectable macrocyclic lactones are effective against sucking lice but may have only limited activity against chewing lice.
  • It is advisable to use the product most suitable for the time of year and cattle management system cattle involved.
  • See the COWS website at for details of products available.

17-12 PFF9

Heavy louse infestations in cattle may be a result of ill-thrift or other underlying causes.


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


Worming ewes at lambing time

· With lambing now well under way, attention should be focusing on controlling parasite burdens in ewes.

· The principle aim of worming ewes is to minimise the future contamination of pastures by worm egg output during the 'peri-parturient rise" (PPR).

· Eggs passed in the faeces of infected ewes hatch and develop into infective larvae, which can cause disease in lambs later in the season.

· Worm faecal egg output is much reduced in well fed ewes in good condition.

· Provision of 'safe grazing' for ewes and lambs available at turnout will also help avoid the risk of worm infections in lambs later in the season.

o 'Safe' pastures should not have been grazed by lambs the previous year and include fields grazed by cattle last year; and re-seeded pastures.

· If only limited safe grazing is available, then this should be reserved for ewes with twin lambs whilst those with single lambs can graze the more contaminated pastures.

· As wormer resistance is becoming more common, advice on worming ewes is changing, influencing both the choice and frequency of treatment post-lambing.

· The timing and choice of wormer are both important in controlling the PPR, as the ewes can quickly become re-infected, particularly when grazing heavily infected pastures post turnout.

· Current worming advice recommends leaving a proportion of the ewes untreated by targeting treatments to include;

o Gimmers and young ewes

o Ewes nursing twins and triplets

o Ewes in low body condition

· Ewes with single lambs or those in good body condition can be left undosed unless there is a risk from fluke or haemonchosis.

· Persistent, or long-acting wormers, which provide a prolonged period of protection if given later in the lactation period before ewes become re-infected from the in refugia population can be highly selective for resistance.

· Worms in refugia include the population of worms present in untreated sheep and the free-living population of eggs and larvae not exposed to wormers.

· The recommendation for long-acting formulations of moxidectin, is to use these products prior to lambing, or at turnout.

Further details can be found on the SCOPS website at

Ewe worming treatments should aim to reduce pasture contamination during the periparturient rise whilst at the same time not selecting for anthelmintic-resistant strains of parasites.

Some ewes nursing singles could be left untreated; seek veterinary advice for your farm.


· Severe outbreaks of nematodirosis can occur in 6 to 12-week-old lambs usually from April to June in some years, depending on prevailing weather conditions.

· Cold late springs followed by sudden changes in temperature can trigger a mass synchronised hatch of infective larvae leading to severe production losses and even death in lambs grazing contaminated pastures.

· Monitor the SCOPS website ( for regular updates on risk of disease in your area.

· As weather conditions during March and April can significantly alter early season predictions of nematodirosis for flocks lambing during March/April, an updated disease risk will be included in the NADIS May parasite forecast.

Nematodirus control

· Control is best achieved by grazing lambs on pasture not grazed by lambs the previous year ('safe pasture').

· Where this is not possible, and local weather conditions are such that an early hatch occurs, then late January/February-born lambs may need prophylactic anthelmintic drenching before the end of March. Consult the SCOPS website regularly for disease risk in your area.

· Late March/April-born lambs may require prophylactic anthelmintic drenching in May if prolonged cold weather during April delays hatching.

· While incidents of wormer resistance have been reported with Nematodirus, white drench (1-BZ) wormers are still generally recommended to control this parasite.

· As disease is primarily caused by developing larvae, faecal egg count (FEC) monitoring is unreliable in determining risk and the need to treat.

· When a white drench (1-BZ) wormer is used in outbreaks of nematodirosis, the FEC of several lambs should be checked 10 days later for the presence of other worm species, which if present, would require treatment with a wormer from another group.


Nematodirus infection in lambs.  These lambs suffered a serious and costly check in growth rate.


· Outbreaks of coccidiosis may be encountered during April in lambs between 4-8 weeks of age, particularly in twin lambs grazing contaminated pastures.

· Coccidiosis is a disease of intensive husbandry with stress a major factor in triggering outbreaks of disease.

· Adverse weather conditions, poor colostrum supply, overcrowding, wet muddy paddocks previously grazed by sheep, and/or extended housing periods all predispose.

· Reduction of stocking densities, batch rearing of lambs, creep feeding and avoidance of heavily contaminated pastures/premises are measures that can be taken to reduce the risk of disease outbreaks.

· Disease prevention can also include strategic dosing lambs on contaminated pastures with diclazuril or toltrazuril at around 3-4 weeks of age, or administration of medicated creep feed containing decoquinate for 28 days.

Liver fluke

· Sheep on premises with known fluke populations, or in high risk areas, should already have been dosed in the autumn and early winter and may need to be dosed again this spring.

· Chronic liver fluke may still be encountered in sheep flocks and can be confirmed by checking for the presence of fluke eggs in faeces.

· On positive farms, the presence of fluke eggs in faecal samples reflects inadequate control of fasciolosis and control should be reviewed.

· Limiting pasture contamination with fluke eggs from patent infections will help reduce subsequent fluke challenge later in the year.

· Flukicides containing closantel, nitroxynil, oxyclozanide or albendazole (at the fluke dose rate), are all effective against adult flukes present during the spring and should be used to reduce reliance on triclabendazole.

· Sheep should always be moved to clean pastures after treatment; and supplementary feeding may be necessary to maintain condition.




· Housed, yearling cattle not dosed in the autumn, may be at risk from type II ostertagiosis towards the end of the housing period.

· Prevalence of clinical disease is usually comparatively low and only a proportion of animals in a group may be affected.


· The disease presents as intermittent diarrhoea with loss of appetite and rapid loss of body weight.

· Mortality in affected cattle can be high unless early treatment with a wormer effective against both arrested and developing larval stages is given.

PGE Control

· Decisions should have been made on the parasite control plan for the forthcoming grazing season.

· Prevention of PGE in growing cattle on a sustainable basis is best achieved by annual rotational grazing (cattle/sheep/crops) but this is not often possible on many farms.

· Parasite control plans based on anthelmintic use may be strategic (early season dosing) or "wait-see" (monitor/treat in the latter part of the grazing season).

· To be effective, strategic worm dosing needs to be initiated at, or around turnout, to limit pasture contamination up to mid-July by which time the over-wintered larval population should have declined to insignificant levels.

o Strategic treatments include administration of a bolus at turnout. or administration of pour-on, or injectable macrocyclic lactones (MLs) at defined intervals.

· Cattle treated strategically should remain set-stocked, or moved to safe pastures (aftermaths) when these become available.

· If "wait and see", then ensure that effective, regular monitoring and diagnostic procedures are in place to act quickly if required.

· Where lungworm is a problem, there is still time to discuss control, including vaccination, with your veterinary surgeon before turnout in most areas.

· Vaccination of calves over two months-old requires two doses of lungworm vaccine four weeks apart with a second dose at least two weeks before turnout.

· For more information see the COWS ( website.


Unless safe grazing is available, dairy calves and suckled calves born during the previous autumn require preventive treatment in their first full grazing season to control PGE

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