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NADIS Parasite Forecast - December

Use of meteorological data to predict the prevalence of parasitic diseases

PF Capture

October came as quite a contrast to the previous month, as the weather became unsettled and wet by the 3rd and remained so through the majority of the month, interspersed with only short periods of drier weather. With winds frequently from the south, this October was another month with well above average temperatures, and notably warm on the 31st.

The provisional UK mean temperature was 11.1 °C, which is 1.6 °C above the 1981-2010 long-term average. This made it the equal-tenth warmest October for the UK in a series since 1910, and only marginally cooler than the Octobers of 2011 and 2013. Rainfall was above average in some areas, particularly across much of Scotland and Cumbria, with double the long-term average around the Solway Firth and the Isle of Man. The overall UK rainfall was 125% of average. Sunshine was rather below normal overall, with a UK figure of 91%. The sunniest areas relative to average were Northern Ireland, the Western Isles of Scotland and the east coast of England. (

December Parasite Forecast/Update

The most recent version of this monthly parasite forecast may be accessed at


  • Outbreaks of trichostrongylosis in store and replacement lambs are a risk if mild wet weather extends into December with farmers not accustomed to drenching sheep so late in the year.
  • Continue to monitor worm egg counts of pooled faecal samples.

Fig 1

Trichostrongylosis in store and replacement lambs is a risk if mild wet weather extends into December.


  • After closantel treatment in November in all regions, fluke treatments can probably be delayed until January when closantel or nitroxynil could be used.
  • Albendazole and oxyclozanide are effective from 10-14 weeks post infestation and can be used when treatment is recommended to remove adult flukes in late spring (often in May).
  • Treatment in May will further limit pasture contamination by fluke eggs reducing the risk of disease later in 2015.


Lice in sheep

  • Louse populations are highest in sheep during late winter.
  • Spread occurs by direct contact.
  • Lice infestations are widespread in most sheep flocks.
  • Use of plunge dipping for other reasons, such as control of sheep scab, cutaneous myiasis and headfly problems, effectively controls louse infestations.
  • Louse infestations can also be controlled with topical application of high cis cypermethrin or deltamethrin but these are best used soon after shearing.

Fig 2

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


Fig 3

Poor flock husbandry and a welfare concern - heavy louse infestation affecting a ewe in poor condition.


Sheep scab

  • Sheep scab is caused by the mite Psoroptes ovis; cattle are rarely affected.
  • Mites are most commonly transmitted by direct contact with infested sheep.
  • Sheep scab can be introduced to a flock by carrier sheep, including purchased animals, sheep returning from grazing, and strays especially on common grazing.
  • Recently infected sheep may not show clinical signs of sheep scab.
  • In most 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.
  • Animals are often seen at different stages of the disease within affected flocks.


Fig 4

Frequent rubbing against fences may indicate sheep scab infestation but is also commonly seen with louse infestations.


Fig 5

Wool along the length of this fence is not normal and warrants immediate investigation.


Fig 6

Animals are often seen at different stages of the sheep scab infestation within affected flocks.

Fig 7

Neglected sheep scab; wool is lost and the skin becomes thickened and covered with scabs.

Treatment of sheep scab

  • Treatment should be discussed with your veterinary surgeon.
  • Plunge dips containing dimpylate (active substance) kill scab mites within 24 hours and affords residual protection for several weeks. 
  • Plunge dipping also treats lice, blowflies, and ticks present on the host.   
  • Macrocyclic lactones (avermectins and milbemycins) given by injection can be effective against sheep scab mites, keds and sucking lice, but have no value for the control of blowflies, chewing lice, chorioptic mange or ticks in sheep.
  • It is essential that all sheep are gathered and correctly treated.
  • Handling pens and fields should be considered as a source of re-infection for at least 17 days after removal of untreated sheep.
  • All additional introduced animals should be treated and quarantined for sufficient time.



  • Out-wintered cattle considered at risk should be dosed for fluke now with a product with some activity against immature fluke.
  • Housed cattle, if not already dosed after housing, may be dosed with closantel or nitroxynil (when housed for 6 weeks or more) or albendazole, clorsulon or oxyclozanide (when housed for 12 weeks or more), thereby avoiding the use of triclabendazole and reducing selection pressure for resistance.
  • Serum or bulk milk ELISA testing and slaughterhouse liver reports, are practical methods of detecting fluke-infected herds.



  • Ostertagia larvae ingested by susceptible stock during the autumn may have halted development and over-winter (as early L4) in the abomasal (stomach) wall.
  • These larvae resume their development in late winter/spring and can cause outbreaks of acute scour with deaths (type 2 ostertagiosis).
  • Susceptible animals exposed to helminth-contaminated pastures during the later 2014 grazing season will be at risk from type 2 ostertagiosis unless they have been dosed with a larvicidal anthelmintic at housing or at least before late winter.
  • Lungworm outbreaks decrease significantly in November. Coughing in unvaccinated susceptible cattle at pasture before housing, or in un-dosed stock after housing, should be investigated for the possibility of lungworm.
  • Autumn-born beef calves should not require anthelmintic treatment at housing.


Fig 8

Susceptible cattle exposed to contaminated pastures during the later 2014 grazing season will be at risk to type 2 ostertagiosis unless they were dosed with a larvicidal anthelmintic after housing.


Fig 9

Autumn-born beef calves should not require anthelmintic treatment at housing.



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