Welcome to NADIS. Are you a...

Vet SQP Farmer/Animal Keeper Industry Professional Researcher Not In Animal Health Industry

You will only be asked this once.

Editorial Information

Professor Mike Taylor BVMS PhD MRCVS DipEVPC DipECSRHM CBiol MRSB

Published 2017

Parasite Forecast - September 2017

17-09 PF Capture

July was an unsettled month with only brief fine spells, starting off warm in the south-east but cool in the north-west. The month ended wet and often quite cool, with some heavy persistent rain at times especially in the south, while in Scotland the weather was mostly bright and showery. The UK mean temperature was 15.1 °C, being slightly warmer than average in the Midlands, East Anglia and southern England, but slightly cooler than average in Scotland.  Rainfall was generally above normal, particularly in the south, and many parts of central southern and SE England had over twice the normal amount.

September Parasite Forecast/Update




  • Warm, wet summers create suitable conditions for the fluke life cycle to take place and snail host
  • populations to rapidly increase, leading to a build-up of infective fluke stages by late summer/early autumn.
  • It is now time to review liver fluke control measures on your farm. Farmers should consult their veterinary surgeons so that there is a plan in place, and the correct drugs, to prevent liver fluke disease this autumn.
  • A UK regional fluke-risk forecast, first developed over 50 years ago, based on summer rainfall and evaporation data, has been issued annually.
  • A new NADIS fluke-risk forecast that calculates monthly and cumulative wetness scores for the summer months (May to October) at a more local level is being  launched this year.
  • The fluke forecast uses data from Met Office Rainfall and Evaporation Calculation System (MORECS) with output to a 40 x 40 km grid covering mainland Britain.
  • Based on the cumulative wetness scores for each grid, a fluke risk map can then be produced with high-risk areas appearing red; medium-risk amber; and low-risk green.
  • Even within these grid areas, local conditions and individual farm circumstances can vary so contact your vet for further information and advice.


17-09 PFF1

Fluke risk map

Acute Fluke Risk

17-09 PFF2

Chronic Fluke Risk

  • Rainfall in all regions of the country has been below average over the winter and spring this year, but the wet June and July has increased the potential fluke-risk this autumn in some regions.
  • Based on rainfall data to the end of July there is potential for a "moderate risk" of fluke infection this autumn in parts of Scotland, Wales, NW and SW England, although the situation may change depending on rainfall during August, September and October.
  • Central and eastern regions of England are currently forecast to be at low-risk.
  • A more accurate prediction of fluke risk will be provided in November when full weather data are available.

17-09 PFF3

Normal liver (left) and chronic liver fluke (right) - develop a liver fluke control plan with your veterinary advisor now; this farmer did not and paid a heavy price.

17-09 PFF4

Normal liver (top) and chronic liver fluke (bottom); flukicide treatment will not repair such severe liver damage.  This situation resulted because purchased sheep were not correctly treated for immature flukes.


Fluke Control

  • Liver fluke disease can be largely controlled by effective drugs administered at the correct time as directed by the farmer's veterinary surgeon as part of the flock health plan.
  • However, evasion strategies should also be adopted wherever possible by not grazing potentially contaminated, poorly-drained areas from late August onwards.

17-09 PFF5

On high-risk farms move sheep from wet pastures where possible from late August
  • Sheep with acute fluke 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.

17-09 PFF6

Post-mortem examination is essential to establish a diagnosis of acute and subacute liver fluke disease, and other potential causes of sudden death
  • Ensure all lambs are vaccinated against clostridial diseases because migrating flukes predispose to Black disease.
  • Farms with a known liver fluke problem, especially in parts of West Scotland, should consult their veterinary surgeons about treating sheep against immature flukes in September.
  • Triclabendazole (TCBZ) is the drug of choice because it is effective against very young immature flukes, however, advice will also be needed where TCBZ-resistance has been previously suspected on farms.
  • The faecal antigen ELISA test can be used to monitor triclabendazole efficacy two to three weeks after dosing and farmers should contact their veterinary practitioner for further advice where drug resistance is suspected.
  • Later fluke treatments could use closantel or nitroxynil especially if TCBZ- resistance is suspected/proven on the farm.
  • Where closantel and nitroxynil are used to prevent liver fluke disease, accurate dosing is essential. Do NOT drench sheep based upon the heaviest animal in the group as toxicity is possible.  Weigh a representative range of sheep and treat according to weight.  Be very careful not to accidentally treat sheep twice.
  • Flocks with no previous evidence of fluke disease must maintain their farm's biosecurity especially with respect to purchased sheep.

17-09 PFF7

Migrating flukes predispose to the clostridial disease "black disease". As well as prophylactic fluke drenching, ensure all lambs are fully vaccinated (twice, one month apart) to prevent clostridial diseases.

Parasitic Gastroenteritis (PGE)

  • PGE is likely to become a problem on contaminated grazing in many areas as larval challenge continues.
  • Monitor lamb liveweight gain or worm faecal egg counts (FEC) to determine the need for anthelmintic treatments.


17-09 PFF8

Parasitic gastroenteritis affecting fattening lambs is more common following wet weather which enables egg hatching and early larval development.

Quarantine Treatments

  • September is the month of most sheep breeding stock sales and quarantine treatments are essential for all introduced stock.
  • Quarantine arrangements are essential to reduce the risk of introducing anthelmintic-resistant worms with purchased sheep.
  • Current best practice involves sequential full dose treatments with either a 4-AD product (monepantel) or 5-SI (derquantel in combination with abamectin), and injectable moxidectin upon arrival on farm.
  • Treat all sheep on arrival and confine for 24-48 hours; then turnout 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.
  • Liver fluke must also be considered in quarantine treatments.
  • Resistance to triclabendazole (TCBZ), appears to be an increasing problem and one that needs managing on all livestock farms.
  • Assume that brought-in animals are infected with resistant liver fluke.
  • Keep newly arrived animals inside, yarded, or on snail free pastures, away from other livestock, for at least 4 weeks and until quarantine treatments have been completed, the animals have been tested, and results show they are free of infection.


17-09 PFF9

Despite their appearance and absence of diarrhoea, quarantine treatments are essential for replacement rams to reduce the risk of introducing anthelmintic-resistant worms.


Fluke Control

  • Fluke control in cattle requires both management and flukicide treatment options, which will depend on prevailing weather conditions, individual farm conditions and varies year to year so consult your vet.
  • Evasion strategies should also be adapted wherever possible, by not grazing outwintered cattle on potentially contaminated, poorly-drained areas.
  • In high fluke-risk areas, grazing cattle may need to be dosed for fluke with a product with activity against immature fluke.
  • Whilst triclabendazole is the most effective against early immature fluke, because acute fluke is rare in cattle, there are several alternatives available, so ask your vet for advice based on local farm conditions and the NADIS fluke forecast.
  • If treated, cattle should be moved onto fluke-free pastures as soon as possible.
  • There are benefits associated with treating cattle at housing as this will immediately remove the impact of developing and adult flukes on growth and feed efficiency.
  • Where this approach is practiced, cattle should be tested later in the housing period for the presence of adult fluke, or given a second treatment to ensure all fluke are removed.
  • Identification of fluke eggs in faeces, serum or bulk milk ELISA testing, and slaughterhouse liver reports, are practical methods of detecting fluke-infected herds. A bulk milk tank ELISA test is an effective way to monitor herd exposure to fluke and efficacy of control programmes
  • The interval between housing and testing or re-treatment will depend on the product used.
  • Very few products can be used in dairy cattle, and veterinary advice should be sort for treatments at drying off and only considered if there is evidence of fluke infection in the herd.


  • Type 1 ostertagiosis presents in growing cattle with profuse diarrhoea suddenly affecting a large percentage of the group.
  • Immediate treatment of all cattle in the group is important when first signs of acute profuse diarrhoea appear.
  • Outbreaks of ostertagiosis can be prevented by targeted anthelmintic treatments based upon liveweight gain, or anthelmintic treatment based upon faecal worm eggs counts.


17-09 PFF10

Diarrhoea and rapid weight loss caused by type 1 ostertagiosis.

Quarantine Treatments

  • Unlike the situation with sheep, there are no specific recommendations for quarantine treatments to prevent the introduction of anthelmintic-resistant worms as resistance is still relatively uncommon.
  • If poor 3-ML efficacy against Cooperia spp. is observed, then treatment with either levamisole (2-LV) or a benzimidazole (1-BZ) may be considered.
  • As for sheep, assume that brought-in animals are infected with resistant liver fluke.
  • The COWS guide to managing liver fluke in bought in cattle involves the three basic principles of HOUSE, TREAT and TEST.
  • Keep newly arrived cattle inside, yarded, or on snail free pastures, away from other livestock, for at least 4 weeks and until quarantine treatments have been completed, and test results show they are free of infection.


  • August and September are peak months for lungworm disease (husk; hoose).
  • Adult dairy cattle which have not built up immunity through natural challenge in previous years are also susceptible to lungworm and may show a sudden and dramatic drop in milk yield.
  • Any animal showing coughing at rest and an increased breathing rate should be investigated for the presence of lungworm.
  • The presence of lungworm larvae in faeces can be readily undertaken by your veterinary practice with results available within 24 hours but note that clinical signs of lungworm may be present before the infection becomes patent.
  • Prompt anthelmintic treatment is essential. All available wormers are highly effective against adult lungworms and parasitic larval stages.


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

Parasite Forecast Related Health Information
Nematodirus in Sheep
Nematodirus is a parasitic infection which causes profuse scour in lambs...
PGE and Lungworm in cattle
Parasitic gastroenteritis usually affects growing cattle during their fi...
Gastrointestinal Nematodes in Sheep
Parasitic gut worms have the potential to cause significant losses in sh...
Liver Fluke Control in Cattle
In cattle, infection is more commonly encountered in beef cows grazing p...
Liver Fluke Control in Sheep
Liver fluke has always been a problem during the late autumn and winter ...
Case Study
Consider targeted parasite control in beef and sheep throughout grazing ...
Case Study
Don’t ignore the threat of lungworm...
Case Study
Prepare for sheep parasite control in the season ahead...
sponsor logosponsor logoImproving Sheep & Cattle Health