Parasitic helminths in sheep (clinial parasitology)

What are the SCOPS principles?

1. Always make sure treatment is fully effective

2. Reduce dependence on anthelmintics using management and monitoring

3. Avoid bringing in resistant worms and/or other parasites by following a robust quarantine routine. Test for anthelmintic resistance

4. Minimise the selection for worms that are resistant to anthelmintics when you treat sheep

How do you make sure anthelmintic treatment is fully effective?

• Avoid under dosing- dose to heaviest

• Check dosing gun

• Correct technique and product

• Perform treatment check

What are some methods used to reduce reliance on anthelmintics?

• Use diagnostic to inform treatment (FECs, DLWG)

• Rotational grazing practices

• Good plan of nutrition

• Manage concurrent disease

• Genetic selection (EBV for resistance to nematodes)

How do you estimate pasture risk using SCOPS table?

How do you minimise the selection for resistance to anthelmintics when you treat sheep?

1. Don't dose and move

2. Use Target Selective treatments (untreated animals contribute to in refugia population)

3. Avoid LA or dual active products without specific indication

Recall the common nematode infections in sheep

Abomasum + more pathogenic

• Telodorsagia circumcincta

• Trichostrongylus axei

• Haemochus contortus

Small intestine + less pathogenic

• Trichostrongylus vitrinus & T. colubriformis

• Cooperia spp

• Nematodirus battus

How do nematodes cause disease?

• Damage gut lining

• Dec absorption and transit time

• Remove nutrients

• H. contortus = blood feeding

• Host immune response

Explain the concept of hypobiosis

• Arrested development L4 stage inside sheep

• En masse emergence and pasture contamination in late winter and early spring

What are the clinical signs of nematode infection?

• Reduced appetite

• Poor weight gain/ weight loss

• Diarrhoea

• Anaemia (Haemonchosis)

• Death

• Fly strike

How does nematodirosis present?

• Acute severe diarrhoea and death lambs 6-12 weeks old

When does teladorsagiosis present (PGE)?

• Type 1- lambs first grazing season, mid summer onwards

• Type 2- yearlings winter months, emergence of hypobiotic larvae

How does trichostrongylosis present?

• Black scour

• Lambs or replacements in autumn winter

How does haemonchosis present?

• Adults and lambs affected

• Acute regenerative anaemia

• Chronic hypoproteinaemia, anaemia, bottle jaw

• Sudden death

Explain the lamb to lamb cycle of Nematodirus battus

• Eggs shed by lambs one year remain on pasture and infect next years lamb

• Overwinter

• Large number L3 hatch simulatenously

How can nematodirus risk be forecast?

Based on daily temperature to point of hatch

• 7 days >10°C

Explain how you would perform a FEC to inform dosing

• Every 2-4 weeks

• Use dung less than 1 hour old

• At least 10 individual samples per group- 10% larger groups

• Representative group, completely rnaodm

• Air expelled from bag and keep cool

What nematode egg counts are not strongly related to clinical disease?

• Nematodirus

Aside for FEC how can you test for haemonchosis?

• FAMACHA score

  • Use pallour of eye mms

• Very high eggs per gram

• Peanut agglutinin assay - distinguishes from other GIN

  

Recall the features of 1-BZs

• Broad spectrum

• Some activity against hypobiosed

• SOME tapeworms

• Flukes at a higher dose

Recall the features of 2-LVs

• Roundworm only

• Limited availability as single active prep

Recall the features of 3-MLs

• Endectoparaciticide

• Parentereral have persistence of activity against certain parasites (check product)

Give an example of 4-AD and a 5-SI. When would you use them

4- Monopantel

5- Derquantel

• Not routinely, as part of a worm control plan, esp as a quaratine dose or late season break drench

What parameter defines anthelmintic resistance?

<95% efficacy- based on actual parasite burdens (FEC)

What are the key factors influencing the development of anthelmintic resistance in a population?

1. Treatment frequency

2. Proportion of population exposed to treatment

3. Under dosing

4. Biosecurity (new strains introduced)

How do you minimise the anthelmintic resitance of worms when treating sheep?

• Dont dose and move- will infect clean pastures with resistant strains

• With products with persistent activity dose and return to conaminated pasture for a few days to pick up susceptible parasites

• Don't treat everything at same time

• Don't treat everything within group - selective treatment

How do you identify the presence of anthelmintic resistance?

• Poor performance and clinical signs

• FECRT - FEC should be zero after drug admin 95%> reduction= resistance

• Drench test- FEC 7-14 days port treatment

What are the issues with cestode infections in sheep?

1. Carcass condemnations at abattoir

2. Echinococcus granulosus - zoonotic

3. Clinical signs in sheep of “Gid” cysts in the brain

What is the only cestode that the sheep is the primary host for?

Monezia expansa

• Farmers may notice bc of segments in faeces

• Can treat with BZs

What are the taenia species that affect sheep?

• Taenia hydatigena

• Taenia ovis

• Taenia multiceps

(Important bc of meat condemnation)

How are taenia tapeworms in sheep controlled?

Dog is intermediate host- CONTROL IN DOGS

• Treat with praziquantel and don't allow access to pasture

Recall the two forms of liver fluke

Acute disease: sick sheep, sudden death

Chronic disease: thin sheep and associated welfare and prod loss

(No immunity in sheep)

What conditions favour live fluke?

• Rain: inc snail habitat, enables miracidial movement, cerceriae dispersal

• Temp: >10°C

When is liver fluke traditionally seen?

May to October

• Changing due to climate change

What causes acute fluke and when?

• 2-6 weeks after ingestion of very large numbers of metcercariae

• Sept-Dec

• Severe haemorrhage due to migration of immature stages though liver

What are the signs of acute fluke disease?

• Sudden death (haemorrhage and shock)

• Weakness

• Pallor

• Dyspnoea

What causes chronic fasciolosis and when?

• Late autumn/winter/spring

• Metcercariae ingested over longer period

• Blood feeding adults in bile ducts (anaemia)

What are the clinical signs of chronic fasciolosis?

• Haemorrhagic anaemia

• Hypoalbuminaemia (bottle jaw)

• Hepatic fibrosis and cholangitis

• 2° clostridial infection Black's Disease

  

How is fluke diagnosed?

• History C/S

• PM + Abattoir reports

• FEC (sedimentation)- 12 weeks post infection so more for chronic

  

• Coproantigen ELISA

• Serum ELISA antibody (can help to time autumn treatment)

• LFT

• Liver enzymes (non specific)

How is fluke treated?

Flukicides - non have persistence of activity so treat and move to low risk pasture

• Triclabendazole- only one that will kill all stages

How can you control fluke?

• Avoid 'flukey pastures' during high risk periods (e.g.- wetlands)

• Monitor risk, on farm disease and treatment efficacy

• Biosecurity