NADIS Parasite Forecast - December 2013
Use of meteorological data to predict the prevalence of parasitic diseases
The first 10 days of November have been 1 or 2 °C colder than usual apart from south-east England, with more than the usual amount of rainfall. Forecasts suggest conditions will remain cold and wet in the north with some snow on the hills, with more settled conditions the south, becoming changeable later in the month.
The second week of December is traditionally wet and windy, and the last week often brings gales and heavy rain or sleet. The intervening weeks are usually quiet and frosty, although these patterns may be changing.
Long-term forecasts are unreliable, but suggest a milder and wetter than average winter in 2013-2014.
December 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 FORECAST
The October data complete the final fluke forecast. This suggests the risk of a high prevalence of liver fluke disease in northern and western Scotland, and Northern Ireland is likely to be at similar risk. Occasional losses due to fluke continue to be forecast in north-western England/north Wales, while the southwest/south Wales region has just fallen out of this category, and joins the rest of the UK, where disease levels are forecast to be low.
Most of the UK dropped from the occasional disease category to the low risk category between the initial (August) and final forecasts due to a period of continuing dry weather.
Another way of assessing the likely risk of fasciolosis is to look at the total monthly rainfall of a region as a percentage of the long-term average. If the sum of the percentages for May, June and July is over 300, and the sum for August, September and October is also over 300, then the forecast risk is high. This condition was not met for any of the regions in 2013, emphasising the lower risk from the summer infection of snails this year.
The return of wet conditions in October may lead to some late snail infections which could overwinter. If May and/or June 2014 are wet, then Mt figures indicate there may be a risk of early disease in the summer of 2014 from the winter infection of snails in Scotland, Wales, western England and most likely Northern Ireland also. A fluke forecast for the winter infection will be produced in early July next year, which will take into account the climatic conditions in the spring/early summer as infection emerges from the snails.
Although most field conditions will have been too dry for fluke and snail development, ditches or permanently boggy ground may still produce high-risk grazing, particularly given the high levels of initial contamination expected following last year's wet conditions. Fencing-off of such areas provides some control of infection without increasing selection for flukicide resistance.
This ewe with subacute fluke disease shows depression, loss of condition and weakness
SHEEP LIVER FLUKE
Deaths due to acute and sub-acute disease may continue into the winter in higher risk situations, with ill-thrift and poor production due to chronic disease likely to be identified throughout the year, but peaking in the winter/spring.
Mean October temperatures across the UK were above 10 °C in all regions, indicating that fluke and snail development will have been continuing. Metacercariae on the pasture will survive and remain infective for a variable length of time, many until the end of December, and some will overwinter. Cases of acute fluke from the summer infection may therefore occur through January or even later, with only a hard frost thought to significantly reduce risk.
This ewe with chronic fluke disease remains quite bright, but is progressively loosing condition
Farms with a history of fluke or those at risk from infection (ideally with evidence of fluke infection from monitoring) should consider a winter (December/January) dose to remove adult and immature fluke, following on from the doses given earlier in the year.
Sheep in high-risk areas may remain exposed to potentially risky pastures through the winter and if so consideration should be given to administering at least one repeat dose to these animals 4-6 weeks later.
Triclabendazole is usually the drug of choice at this time of year, as it is effective against young immature fluke. It is important to monitor for flukicide resistance as this is an increasing concern with this drug. If risk is assessed to be lower, then it may be best to use one of the other drugs with activity against immature fluke (closantel, nitroxynil), even though they are less effective against young immature fluke
Subacute fluke disease around mating time can be a cause of reduced scanning percentage in ewes, increasing barren rates and reducing twinning percentage
The treatment of any outbreaks of acute or sub-acute fasciolosis should involve a move to fluke-free ground if possible. If closantel or nitroxynil rather than triclabendazole are used to treat disease then follow up treatments are usually needed to remove those fluke too young to be treated by the first dose. If a move is not possible, then treatment will be needed throughout the risk period, perhaps even every three weeks in the highest risk situations.
There are likely to be fewer worm larvae on pastures in December than there were during the late summer/autumn, but many pastures may be infective enough to cause disease and poor growth during the winter. Below about 5 °C, the worm larvae are inactive and don't cause many problems, but temperatures can't be relied upon to stay below this level at any time of year, particularly during a milder winter such as the one suggested for 2013-14 by long-term forecasts.
Below about 5 °C, worm larvae are mostly inactive and are not very infective
Third stage larvae survive well in cold and wet conditions, with pasture levels reducing more quickly in the spring as the temperature begins to rise. Although the warmer climate has extended the period of the year during which eggs can develop, temperatures below 10 °C allow very little development from egg to third stage larva.
Faecal egg count monitoring of batches of grazing store or replacement lambs is an invaluable tool in controlling PGE, and can help avoid the unnecessary use of anthelmintics (see SCOPS guidelines). It is also an important part of the investigation of poor growth rates in these animals. Around ten fresh samples can be collected from the pasture following gathering in a field corner for ten minutes and these can be examined at the laboratory, vet practice or on farm, ideally individually or otherwise pooled. Decisions about dosing and further sampling can then be made with veterinary advice.
Faecal egg count monitoring is an invaluable tool in controlling PGE
The late return of wet conditions this year may have increased the exposure of stock to late Haemonchus contortus infection. This is likely to remain as inhibited larvae in the animals over the winter. This means that acute haemonchosis becomes less of a risk as the weather becomes colder, but the inhibited larvae can emerge in the spring causing type 2 disease around lambing time with potentially serious consequences. Investigating the presence or absence of Haemonchus on a farm is an important part of the flock health plan.
CATTLE LIVER FLUKE
See also general fluke forecast above
Diagnoses of liver fluke in cattle usually increase through the autumn to reach relatively high levels by December, and reach maximum levels around February/March (VIDA 2002-2012).
Cows affected over the winter will show condition loss and reduced fertility. Dairy cows will also suffer reduced milk yield/quality and increased metabolic disease.
The treatment of dairy cattle in milk is currently limited to adulticides (albendazole and oxyclosanide) with a 60 or 72 hour milk withdrawal respectively. In addition, some triclabendazole preparations (but not all) may be used early in the dry period. Please check data sheets or with a qualified person for advice.
Liver fluke in cattle causes loss of condition and loss of appetite often in the winter. There is a swelling under the chin in some more advanced cases (bottle jaw)
The need for control measures should be assessed on local and farm history, and monitoring by egg counts, post-mortem examination or abattoir feedback and individual or bulk milk serology.
For control, cattle housed around 6 weeks ago may be given a closantel or nitroxynil treatment now that the flukes are at least 6 weeks old. Depending on previous treatments and grazing conditions, out-wintered cattle may require a December/January flukicide treatment effective against adult and immature fluke.
The dry summer is likely to have led to a lower challenge with Ostertagia in grazing youngstock this year. However, the return of rains in October will have released larvae from crusted faecal pats and this late challenge risks the build-up of large numbers of inhibited larvae within the cattle. There is a therefore an increased risk of type 2 ostertagiosis this year in any youngstock that grazed contaminated pastures in the autumn and did not receive a larvicidal dose of anthelmintic at housing.
This may be a particular issue for calves moved back to earlier grazings prior to housing. The housing dose also clears any lungworm infections that are present. In most cases, adults do not need a housing dose although this may have implications for ectoparasite control and veterinary advice should be sought. Group 3 (macrocyclic lactone) wormers are usually recommended for the housing dose due to their larvicidal activity. Outwintered cattle should not be left on potentially heavily contaminated grazing.
The incidence of lungworm disease in December usually falls to low levels again after its peak in August to October. Coughing in grazing or undosed housed animals should still be investigated. The stormy weather often seen in December may release larvae onto the pasture, leading to local high-risk conditions for susceptible out-wintered stock.
Phil Scott DVM&S, DipECBHM, CertCHP, DSHP, FRCVS
Lice in Cattle
Infestations with lice affect all cattle-producing countries and can cause production losses due to reduced feeding time and damaged hides (Fig 1). Louse populations are highest in cattle kept indoors during the winter months and those in poor body condition rather than the reverse situation where lice cause debility.
Treatment uses a pour-on synthetic pyrethroid or organophosphate preparation. Injectable group III anthelmintics (ivermectin, doramectin and eprinomectin) will remove all sucking lice and >98 per cent of biting lice, and all lice when used as pour-on preparations. All cattle in direct contact must be treated.
Group 3 (macrocyclic lactone, ML) wormers are usually recommended for the housing dose due to their larvicidal activity and efficacy against lice.
Local farm conditions may vary so consult your veterinary surgeon. Parasite control should be part of your veterinary health plan
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