NADIS Parasite Forecast – February 2013

Use of meteorological data to predict the prevalence of parasitic diseases

The mean UK temperature for December 2012 was exactly equal to the 1961-90 long-term average for the month. England and Wales were around 0.3 °C milder than average, while Scotland was 0.5 °C colder, and Northern Ireland 0.2 °C colder. Temperatures over the October-December period have been below average in most regions, with south-eastern and central southern England the only region slightly milder than its 1961-90 long-term average for the month.

It was one of the wettest Decembers of recent years, with UK rainfall figures of 155 per cent of the 1961-90 long-term average. England was particularly affected, at almost 180 per cent of expected rainfall.

The three-month rainfall figures show that most regions have been significantly wetter than expected, with northern Scotland and Northern Ireland the only exceptions.

Temperature: December 2012 (as °C Above/Below Regional Average 1961-1990)

Temperature: October - December 2012 (as °C Above/Below Regional Average 1961-1990)

Rainfall: December 2012 (as % Above/Below Regional Average 1961-1990)

Rainfall: October - December 2012

(as % Above/Below Regional Average 1961-1990)

The first week of January has seen very mild temperatures, however; this is expected to change with the imminent arrival of cold conditions. The rest of January is expected to be colder than average with a risk of significant snowfall.

Any late January gales and snow often cease during early February and the second week usually sees high

pressure and cold temperatures. Northerly conditions with low pressure and snow are often seen during the last week of February.

February Parasite Forecast/Update David Wilson MA BVMS DSHP DipECSRHM EVS MRCVS, R(D)SVS Farm Animal Practice

The most recent version of this monthly parasite forecast may be accessed at www.nadis.org.uk.

LIVER FLUKE IN SHEEP The very wet summer conditions will have resulted in heavy contamination of many pastures with liver fluke infective stages during the summer and autumn. These infective stages (metacercariae) are a major risk to livestock. Significant risk to stock will extend into February in many situations, particularly as conditions have been quite mild without a prolonged freeze. If a significant freeze over several days does occur, this should help to reduce risk to stock.

Sheep on infected premises will have picked up infection over the late summer, autumn and winter. There have been many losses due to the effect of these

young fluke damaging the liver (acute disease). A tenfold increase in acute liver fluke disease cases has been seen by AHVLA in the last quarter of 2012 compared to the same period of 2011, as reported by SCOPS.

Many infected animals will subsequently suffer from chronic fluke disease, causing ill thrift and poor production if not effectively treated. Chronic cases are seen in every month of the year but usually peak in the late winter/spring.

Regional Weather

(based on Met Office figures)

REGIONS

0 N W Scotland

1 E Scotland

2 N E England

3 E Anglia

4 The Midlands

5 S England

6 S W Scotland

7 N W England

& N Wales

8 S W England

& S Wales

9 N Ireland

Improving Beef and Sheep Health

Submandibular oedema (bottle-jaw) is often seen associated with chronic fascioliasis

Animals should be monitored for indicators of infection; faecal samples from around 10 ewes should identify surviving infection acquired during the peak of pasture infectivity in the autumn and indicate the need to treat the group. More recent infection is harder to detect, but post mortem and abattoir data, or blood tests to show liver damage or previous exposure to fluke may be used as well as keeping a close eye out for disease, which may show as several animals becoming dull and failing to thrive, or poor scanning percentages.

Treatment at or after housing with an appropriate flukicide should be discussed with your vet, as should the approach to those animals remaining out on risky pastures, as acute disease can continue to occur through into March in some years e.g. 2009. In more normal years, stock are often moved back onto potentially higher-risk pastures at this time, as the risk is presumed to be much reduced. This may well not be the case this year.

COCCIDIOSIS

This is caused by microscopic parasites called coccidia, and is associated with high stocking rates. This year, factors such as shortage of bedding and potential nutritional problems could lead to an increased risk of coccidiosis. Other factors are poor levels of hygiene and other disease or nutritional problems.

The common signs of coccidiosis are rapid weight loss and diarrhoea containing mucus and flecks of blood causing staining of the perineum and tail.

Disease may appear in February, in intensively reared January-born lambs, particularly in heavily stocked sheds. Lambs show scour, dullness and abdominal pain, while some may die. Chronic disease may cause simply wasting and poor appetite. Gut damage can lead to continued poor growth, even after treatment.

The early-born lambs tend to pick up infection passed by the ewes and increase the environmental contamination, often without becoming ill. Disease is then more common when later-born lambs are exposed to this increased level of infection.

Diagnosis and treatment are not always straightforward, so veterinary advice should be sought. An important part of treatment will be moving the lambs from the highly contaminated environment if possible.

Preventative measures should address the stocking and hygiene points mentioned above and may include a prophylactic treatment of all lambs around four or five weeks of age, or medicated creep feed.

SHEEP NEMATODES

Parasitic Gastroenteritis (PGE)

Although PGE disease may occur in any month of the year, the risk is relatively low when temperatures are below 5 °C as worm larvae are largely inactive. Current risk may be further reduced by the presence of snow. These inactive larvae can actually survive the winter well, and they may contribute heavily to the infective pasture larval population in the spring.

Milder spells may lead to a continuing risk of PGE in store lambs and hoggs through the winter, particularly on paddocks heavily contaminated earlier in the season; for example, by an outbreak of clinical PGE. This can continue into February given suitable conditions. The need to dose outwintered store or replacement lambs during the winter can be assessed using faecal egg counts. Adult sheep may also develop PGE during the winter, often concurrently with diseases such as fascioliasis or Johne’s disease, nutritional stress and/or late pregnancy.

Milder spells may lead to a continuing risk of PGE in outwintered stock

Contaminated pastures can only be considered “safe” after the majority of larvae have died. Rising spring temperatures cause the larvae to become more active

and, if they are not ingested by a potential host, they use up their energy reserves and die. This often begins to occur around April, with pastures classed as low-risk from late June if no sheep have grazed them in the spring, or medium risk if grazed in the spring by adult non-lactating sheep.

A veterinary parasite control plan for the forthcoming grazing season should be formulated on an individual farm basis including identifying any safe grazing available at turnout in spring (e.g. last year’s cattle pastures) or in midsummer (e.g. aftermath for weaned lambs). Following the guidelines in the Sustainable Control of Parasites in Sheep (SCOPS) manual should reduce selection for anthelmintic resistance.

LIVER FLUKE IN CATTLE

Very many cattle will have been exposed to high levels of liver fluke challenge when at grass. This does not often cause acute disease as it does in sheep, but causes chronic fluke disease leading to weight loss, poor growth and poor production which can be found at any time of year, but there is a peak of cases over the winter.

Faecal egg identification, blood tests and bulk milk tests in dairy cows can be used to monitor herds for levels of infection, in addition to keeping a close eye out for signs of disease mentioned above perhaps also with anaemia, bottle jaw, poor fertility and poor milk yield or metabolic disease in dairy cows.

Liver fluke (Fasciola hepatica) egg

Any winter treatments in housed or outwintered cattle will depend on the previous treatments as well as the likely risk, and should be discussed with your vet. It should be borne in mind that grazing cattle may have been exposed to fresh infection after any previous treatments, and housed cattle may still be carrying infection that was too young to be killed by treatments given at or after housing.

As with sheep, in more normal years outwintered stock are often moved back onto potentially higher-risk pastures at this time, but this may be too dangerous this year.

The number of chronic fluke cases peaks over the winter

CATTLE NEMATODES

Calves and yearlings may have been exposed to high levels of worm infection when grazing in the autumn this year. At that time of year, most of the infection that is picked up becomes inhibited in the stomach wall of the cattle, and doesn’t go on to cause immediate disease. The problem may occur now, in late winter/spring, as these larvae begin to develop again. If large numbers emerge from the gut wall at the same time, then disease can result, with watery scour and dehydration (Type 2 ostertagiasis). Often only a small proportion of the group is affected, but those animals are often severely ill and some may die. Very occasionally, adults may be affected.

Youngstock old enough to have been grazing in the autumn may be at risk of Type 2 ostertagiasis in late winter unless they received an effective housing anthelmintic

Cattle may be particularly at risk if they were returned to pastures before housing that they had grazed earlier in the season.

Anthelmintic treatment of youngstock at housing is mainly given to prevent this disease, and must be with a drug effective against inhibited larvae; group 3 (ivermectin-type) drugs are usually recommended. Affected animals may have a low or zero worm egg count, but blood tests (pepsinogen) may indicate worm damage to the abomasum.

ECTOPARASITES

Phil Scott DVM&S, DipECBHM, CertCHP, DSHP, FRCVS

Sheep Scab

Sheep scab infestations causes rapid weight loss. Increased feeding to restore body condition proves expensive.

It is estimated that in some regions where there are high densities of sheep farms, up to 50% of flocks may be affected annually. Economic losses accrue due to increased feed costs to compensate for rapid loss of body condition. Low lamb birthweights and mortality rates occur in lambs born to ewes with severe sheep scab during pregnancy. Slaughterhouse condemnation of carcases and downgrading of leather can further add to financial loss.

On a flock basis, sheep scab is characterised by intense itching, with repeated rubbing of the shoulders and flanks along the ground or against fences, foot stamping, clawing at the flanks, and biting the shoulders. Tufts of wool are characteristically seen on fences and hedges.

As the disease progresses, wool is lost and the skin becomes thickened and covered with scabs.

Veterinary confirmation of Psoroptes ovis is essential. There are well-proven and effective prevention measures which must be part of the veterinary flock health plan.

Maintain a closed flock wherever possible.

Maintain secure double-fenced perimeters where they contact other fields containing sheep.

Treat all purchased sheep upon arrival on farm and quarantine for the correct time.

Investigate all cases of pruritus and fleece loss.

Lice and sheep scab often occur on the same poorly-managed premises

Treatment

Treatment strategies vary between farms and must be discussed with your veterinary surgeon.

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

NADIS seeks to ensure that the information contained within this document is accurate at the time of

printing. However, subject to the operation of law NADIS accepts no liability for loss, damage or injury

howsoever caused or suffered directly or indirectly in relation to information and opinions contained in or

omitted from this document.

To see the full range of NADIS livestock health bulletins please visit www.nadis.org.uk

Copyright © NADIS 2013

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