Parasite Forecast

Issue: October

Weather report

The initially dry but latterly unsettled weather experienced in August has seen a return to more typical conditions for parts of the UK, whilst in others the warmer, drier weather experienced so far this season has continued. The overall UK average temperature in August 2018 was 15.3°C, 0.3°C above the long term average (1981-2010 data), whilst rainfall for the UK was 95% of the long term average.

Regionally, average temperatures were comparable to the monthly average for all regions of Scotland and Northern Ireland, and above average for all regions of England and Wales. The average temperatures over the previous 3 months (June – August 2018) was above average across all regions. Rainfall varied around 10-20% above and below the long term average across all regions, while the average rainfall for all three previous months was below the long term average for all regions.

Liver fluke: provisional Autumn forecast

The provisional fluke forecast for Autumn 2018 is based on monthly rainfall and temperature data from May-August 2018.

This provisional forecast is currently predicting low risk across the UK at the regional level (Figure 1), although it should be noted that some parts of western Scotland have been flagged as medium to high risk. These risk levels may change based on the weather experienced in September and October.

Figure 1: Current regional risk for liver fluke in Autumn 2018 is low. However, local conditions should be taken into consideration when evaluating on farm risk

It is important to note, as highlighted in a recent joint press release issued by the working groups for sustainable parasite control in sheep and cattle (Sustainable Control of Parasites in Sheep or “SCOPS” and Control Of [cattle] Worms Sustainably or “COWS”), that local factors must also be taken into account when considering on farm risk from liver fluke. The dry hot weather does not necessarily guarantee low infection levels on all farms or even between different areas on individual farms.

Development of liver fluke and its intermediate host, the mud snail (Galba truncatula; Figure 2) on pasture is dependent upon temperature and rainfall with warm wet conditions optimal. On farms with permanently wet areas and/or permanent water bodies snails may therefore continue to thrive in hot weather.

Figure 2: A large number of mud snails (Galba truncatula) recovered from a farm in Lancashire, August 2018. While the current dry weather indicates lower risk for liver fluke consideration should be given to on farm conditions relating to local rainfall and wetlands. Photo credit: Bethan John, University of Liverpool.

Despite the overall low predicted risk, continued vigilance for signs of disease and on farm contingency plans in the event of an outbreak are of great importance at this time of year in the context of liver fluke on your farm.

Advised actions include:

  • Monitoring for signs of disease:
    • Sudden death in heavy acute infections
    • General dullness, anaemia and shortness of breath
    • Rapid weight loss, fluid accumulation
  • Routine diagnostic testing to give a greater insight into the current infection:
    • Post-mortem in acute outbreaks (Figure 3).
    • Antibody ELISAs are available for testing individual sheep and cattle through blood sampling, or to monitor herd-level infection status in dairy cattle through testing bulk milk tank samples.
    • A faecal antigen test is also available for testing individual animals.
    • Worm egg counts can be used to diagnose infection in individuals, or groups of animals when using a composite sample. However, these cannot be relied upon for the diagnosis of acute disease, which is more common in the autumn months.
    • For more information on diagnostic options, please speak to your vet.

Figure 3: Acute liver fluke infection may be easily detected at post-mortem as parasitic tracks on the liver. Acute disease is more common in sheep (pictured) compared to cattle. Where outbreaks of disease occur, post-mortem of lost stock is a useful way of confirming diagnosis and ensuring correct treatment.

 Where acute disease occurs, treatment with triclabendazole is recommended as this is the only product effective against both adult and immature stages of the parasite.

    • It is also advised to test for treatment efficacy through pre- and post-treatment diagnostic testing. For more information about efficacy testing, please speak to your vet.
  • Risk of infection can also be reduced by identifying high risk fluke pastures and avoiding grazing these during peak risk periods.
    • Both sheep and cattle are susceptible to infection with liver fluke, meaning pastures previously grazed by either species should be considered a potential risk to the other.
    • Mud snails are generally found in damp, muddy areas.

Buying in livestock: quarantine treatments

All animals coming onto farm should be considered a potential source of parasites. Where buying in new stock, quarantine measures should be taken. This includes worms, for which the introduction of resistant strains is of particular concern, and ectoparasites (i.e. lice and mite infestations) such as a recent outbreak of Psoroptic mange in cattle reported in September 2018 by the Animal and Plant Health Agency’s Veterinary Investigation Centre in Carmarthen.

For sheep, current best practice advised by SCOPS is as follows:

To prevent introduction of resistant roundworms and sheep scab:

  1. Sequential treatments with either a 4-AD product (monepantel) or 5-SI (derquantel in combination with abamectin), and injectable moxidectin.
  2. Hold purchased animals away from pasture for 24-48 hours post treatment, then turn out to “dirty” pasture previously grazed by sheep.
  3. Maintain purchased stock separately for at least 30 days to monitor for disease before mixing.

Where resistant liver fluke is a concern:

  1. Triclabendazole resistance is increasingly common in the UK. Assume that brought-in animals are infected with resistant liver fluke.
  2. Hold purchased animals away from pasture, or on grazing free of mud snails (dry, well drained pastures) until at least 4 weeks after treatment.
  3. Treat animals with either:
    1. 2 doses of closantel, 6 weeks apart
    2. 2 doses of nitroxynil, 7 weeks apart
    3. Alternative strategies using a combination of products may help prevent introducing resistance to any one particular flukicide. For more advice on this, please seek veterinary advice.

For cattle, COWS guidelines highlight the importance of knowing disease status of purchased animals or their farm of origin.

  1. For roundworms, particularly those infected with lungworm and/or 3-ML resistant Cooperia:
    1. House animals on arrival and implement control measures ahead of turn out in spring.
    2. Treat with effective anthelmintic. N.B. for 3-ML resistant Cooperia, treatment with either a 1-BZ or 2-LV product is advised.
    3. Test efficacy of treatments
  2. For ectoparasites such as mites and lice, treat with a 3-ML or permethrin product to prevent spread during winter housing
  3. For liver fluke, specific guidelines have been developed for bought in cattle based on the three basic principles of HOUSE, TREAT and TEST.

For more information concerning the implementation of effective on farm quarantine procedures please speak to your vet.

Roundworm infections

Whilst the warm and dry summer months have resulted in to relatively low risk season for roundworm infections in grazing livestock, recent unsettled spells of rainfall and continued warm weather may introduce some risk into the late grazing season. Many of the disease-causing roundworm larvae will remain infective on grazing pastures to the end of the season. It is therefore important to maintain vigilance for signs of disease in at risk animals grazing potentially contaminated pastures:

SHEEP

Parasitic Gastroenteritis (PGE) and haemonchosis

PGE is a disease of lambs in their first grazing season, whilst haemonchosis may affect both lambs and ewes.

Advised actions include:

  • Monitoring for signs of disease:

PGE:

Haemonchosis:

  • Loss of appetite
  • Diarrhoea
  • Dehydration
  • Weight loss
  • Sudden death (acute infections)
  • Anaemia and general fatigue (Figure 4)
  • Oedema or fluid accumulation (e.g. bottle jaw)
  • Progressive weight loss and loss of appetite (chronic infections)

 

Figure 4: Anaemia can be seen as pale mucus membranes, particularly around the eyes. Anaemia is a common sign in heavy infections of blood feeding parasites such as Haemonchus contortus and Fasciola hepatica.

  • Consider worm egg counts if infection status is unknown
  • Where anthelmintic treatments are required:
    • Move to safe pasture (eg. silage aftermath) if available.
      • Leave animals on dirty pasture for 2-3 days prior to moving.
      • Aim to leave at least 10% of the flock untreated
    • Check efficacy through worm egg counts:
      • Re-test 10-12 individuals at 7-14 days post treatment depending upon the product used.

CATTLE

Lungworm

Lungworm larvae may survive drier periods of weather within faecal pats to be dispersed onto pasture en masse following periods of rainfall, such as those recently experienced. Cases have been recently detected in Scotland (Figure 5) and, naïve animals such as unvaccinated calves in their first grazing season or bought-in dairy cattle on farms with a known history of disease could still be at risk.

 

Figure 5: Clinical cases of lungworm similar to above have been detected in parts the UK in September 2018.

Advised actions include:

  • Monitoring for signs of disease:
    • Widespread coughing in the group, initially after exercise then at rest
    • Increased respiratory rate and difficulty breathing (Figure 6).
    • Rapid loss of weight and body condition.
    • Milk drop in lactating cattle
    • Death in heavy infections
  • Where infection is suspected, treat animals with an anthelmintic and remove affected cattle to “safe” pasture (e.g. aftermath) or house in a well ventilated building.

Figure 6a and 6b Early signs of lungworm infection include widespread coughing and elevated respiratory rates.

Dosing at housing

Housing presents an opportunity in the ongoing control of parasitic disease on farm. Worm burdens acquired over the grazing season may be targeted effectively at this time without risk of animals becoming re-infected. There are also benefits on growth and feed efficiency associated with treating cattle for fluke at housing. As is the case during the grazing season, any treatments administered should be based on evidence of infection, such as clinical disease and/or diagnostic testing (e.g. worm egg counts).

Treatment efficacy should also be considered at this time since ineffective treatments may result in a continued parasitic burden (with associated reductions in productivity) and potential pasture contamination with resistant parasites at turn-out the following grazing season.

  • For growing cattle housed after their first or second season treatment with products containing either a Group 3-ML or Group 1-BZ anthelmintic is recommended at housing. These products are effective against encysted stage larvae acquired in the latter stages of the grazing season. If untreated, heavy burdens of encysted larvae can cause type-2 ostertagiosis in later winter or the following year due to triggered mass emergence.
    • Encysted worm burdens cannot be assessed by worm egg count.
  • Whilst housing effectively eliminates risk of infection with pasture associated parasites such as intestinal roundworms and flukes, risk of louse infestations may increase at this time since these parasites can spread directly from animal to animal very easily once they are penned in close proximity to one another in what are relatively dry, warm conditions. Group 3-ML pour-on preparations have the added advantage they are also effective against both sucking and chewing lice (Figure 7).
  • Cattle exposed to liver fluke infection can either be dosed with a product other than triclabendazole either at housing, or at a delayed interval post-housing. Provided levels of infection are not too severe, the latter option is more desirable in the context of drug resistance, since it allows triclabendazole to be used more sparingly, preserving its efficacy on farm for when it is most needed (i.e. in acute clinical disease).
    • If using a product other than triclabendazole it will be necessary to either repeat or delay treatment so that all flukes are of a sufficient age for the drugs to be fully effective. For example, if treating with closantel COWS recommend delaying treatment for 6-7 weeks post-housing before treating.
    • Some of these alternative products, such as albendazole,  oxyclozanide also have the added benefit of being licenced for use in lactating animals provided milk withhold periods are observed. It is important to check labelling of individual products.
    • Whichever product is ultimately used, cattle should be tested later in the housing period to assess treatment efficacy.

For more information please speak to your vet, or visit the COWS website.

Figure 7: Pour-on preparations of 3-ML wormers are also effective in controlling sucking and chewing lice.

John Graham-Brown BVSc MSc PhD MRCVS
October 2018

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