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Editorial Information

Professor Mike Taylor BVMS PhD MRCVS DipEVPC DipECSRHM CBiol MRSB

Published 2017

Parasite Forecast - November 2017

17-11 Capture

September started off dry and sunny in many parts of Britain, but the rest of the month was unsettled, with an unusually high number of rain days across England. The UK mean temperature was 0.1 °C below the long-term average of 12.6 °C for the month.   Rainfall was mostly above normal except in parts of SE England and NW Scotland, with over double the average amount in the extreme SE of England.

November Parasite Forecast/Update


Liver Fluke Forecast

  • The updated regional fluke forecast, based on rainfall to the end of September, indicates the potential for a "high-risk" of fluke infection in North and West Scotland and South Wales this autumn; and "medium-risk" in the Scottish borders, North Wales and parts of NW and SW England.
  • Central and eastern regions of England are currently forecast to be at "low-risk".
  • The situation may change depending on rainfall in October and the final regional fluke-risk forecast will be issued next month.

17-10PF F1

  • An earlier forecast for acute fluke disease issued with the September forecast and based on regional weather data in August to October last year, and May and June this year, predicted that localised areas of Western Scotland, and North Wales were at "high-risk".
  • As well as the regional fluke forecast, more local NADIS forecasts will be produced in November.
  • More detailed information will be made available through veterinary practices


17-11 PFF2


Liver Fluke

The recommendations for liver fluke treatments for November/December are:

  • Triclabendazole (TCBZ) is the drug of choice in cases of acute fluke disease because it is effective against very young immature fluke stages.
  • A second treatment with TCBZ is likely to be necessary in parts of Scotland and South Wales where there remains a very high liver fluke disease risk.
  • Where TCBZ- resistance is suspected, treatments from November onwards could include either closantel or nitroxynil, which are active on later immature (> 6-7week-old) and adult fluke.
  • Fluke faecal egg count reduction tests to detect TCBZ- resistance are unreliable in acute fluke infections as eggs don't start to appear in faeces until 10-12 weeks post-infection.
  • Instead, the coproantigen ELISA test can be used two to three weeks after dosing and farmers should contact their veterinary practitioner for further advice where such drug resistance is suspected.
  • Farmers in other regions of the UK should consult their veterinary surgeon about fluke treatment as action may be necessary during November if treatment has not already been given.

Signs of Acute Fluke Disease

  • Sheep with acute fluke infestation, in which there are large numbers of immature flukes, may simply be found dead without prior signs of illness therefore it is important to have all sudden deaths investigated to allow immediate preventive measures.
  • Post-mortem examination is essential to establish a diagnosis of acute fluke.
  • Less severe clinical signs include reduced grazing, rapid weight loss, weakness, abdominal pain and anaemia.

17-11 PFF3

Less severe clinical signs of subacute liver fluke diseases include rapid weight loss, abdominal pain and anemia.


17-10 PF F3
Anaemia (pale mucous membranes) caused by liver fluke disease

Parasitic Gastroenteritis (PGE)

  • Prolonged wet and mild weather will give rise to flushes of infective worm larvae on pastures.
  • Outbreaks of trichostrongylosis are often seen from late October onwards in store and replacement lambs, and sometimes yearlings.
  • Heavy infestations cause black foetid diarrhoea (black scour) and rapid weight loss.
  • Sudden outbreaks of haemonchosis can occur as the female worms are prolific egg-layers, resulting in high FEC and rapid pasture contamination under optimal conditions.
  • With reports of sporadic cases this autumn, look out for affected sheep showing clinical signs similar to acute fluke, including sudden death.
  • Monitor lamb liveweight gain (LWG) or worm faecal egg counts (FEC) to determine the need for anthelmintic treatments.
  • As the weather becomes colder, most acquired Haemonchus larvae will inhibit in the abomasal wall of the host sheep resuming development in the spring if left untreated but note that arrested larvae do not produce eggs so FECs may be negative.

17-11 PFF5

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


17-11 PFF6
Trichostrongylosis can also affect gimmers in the late autumn/winter



Consult your veterinary surgeon about wormer choice before moving fattening lambs onto catch crops

Anthelmintic treatments post tupping

  • A faecal worm egg count will decide whether anthelmintic treatment is necessary in rams after mating; marked condition loss may compound parasite problems.

17-11 PFF8

This ram has lost a great deal of condition over a 7-week mating period.  Worm FEC will decide whether rams require worming after tupping.




17-11 PFF9

Severe liver fluke infestation.  Treatment of housed cattle may need to be repeated or delayed after housing, to ensure all flukes are removed.


  • Growing cattle housed after their first or second season at pasture should be treated with products containing either a Group 3-ML or Group 1-BZ anthelmintic at housing, which are effective against inhibited worm larvae.
  • Group 3-ML pour-on preparations have the added advantage they are also effective 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.


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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