Parasites Of Sheep

Question 1

What parasite typically causes scour in lambs in August to September following ingestion of larvae on the pasture in July?

Answer 1

Telodorsagia circumsincta
- type 1 disease seen in August to September

• type 2 disease seen in late winter / early spring the year after exposure

Question 2

What is the source of telodorsagia circumsincta?

Answer 2

Ewes - periparturient egg rise

Question 3

What parasite typically causes high morbidity, high mortality acute diarrhoea in 4-12 week old lambs in May-June time?

Answer 3

Nematodirus battus

Question 4

What parasite causes acute weakness, anaemia and sudden death in Autumn?

Answer 4

Fasciola hepatica

Ddx haemonchus

Question 5

What parasite causes weight loss, bottle jaw and anaemia in January to May?

Answer 5

Fasciola hepatica (chronic)

Question 6

What is the epidemiology of nematodirus battus?

Answer 6

Source - eggs from lambs on pasture in the previous year
Hatching occurs after a period of chill and mean day / night temperature of greater than 10c
Overwinter and ingested by lambs in spring
Cause disease in May - July

Question 7

What parasite causes black scour in lambs or replacements in late autumn / winter?

Answer 7

Trichostrongylus vitrines
Trichostrongylus colubriformis
Trichostrongylus axei

Question 8

What parasite causes disease in both adults and lambs?

Answer 8

Haemonchus contortus

Question 9

At what age do lambs start developing immunity to parasites?

Answer 9

5-6 months

Question 10

When does peri-parturient immunosuppression occur in the ewe?

Answer 10

2-4 weeks before lambing, until 6-8 weeks after the end of lactation

Question 11

What population of ewes should you leave in refugia?

Answer 11

10%

Leave the single bearing ewes - less immunosuppression

Question 12

How can you avoid under dosing sheep?

Answer 12

Weight and dose to the heaviest animal 
Ensure that the gun is calibrated
Use a good dosing technique 
Put on yard for 24h post treatment 
Dose into the oesophagus

Question 13

When should you dose sheep?

Answer 13

Autumn
Winter
Early spring

• can coincide with lambing time and scab treatment

Question 14

What is the SCOPs guidelines to reducing resistance on farms?

Answer 14

Work out targeted control strategy 
Use quarantine 
Test for anthelmintic resistance
Administer correctly
Use anthelmintics only when necessary
Select appropriate anthelmintic for task
Adopt strategies to preserve susceptible populations 
Reduce dependence

Question 15

How should you control parasites in lambs that are born in January and finished outside in May / June?

Answer 15

Nematodirus risk
Assess pasture risk
- if turned out onto pasture not grazed by lambs in the previous 2 years then no treatment is required

If turned out on dirty pasture
- dose Benzamidazoles - every 15 days (PPP) April - June
- could suggest to combine this with weighing
(not moxidectin - resistance)

Perform FEC every 3-4 weeks - check for coccidia
Also consider coccidiostats - diclazuril / toltrazuril

Question 16

Devise a worming strategy for lambs born in February / March which are finished outside in March - July?

Answer 16

Nematodirus risk
Telodorsagia, Trichostrongylus and Haemonchus - peak in later Summer so not a concern

Turn out on to pasture not grazed in past 2y if possible
Benzamidazoles q 15 days from turnout until June
Perform FEC every 3-4 weeks and check for coccidia - diclazuril / toltrazuril if required

Question 17

What parasite prophylaxis should you provide for lambing in March and turnout March - May, finished in July?

Answer 17

Nematodirus risk
Telodorsagia, trichstrongylus and haemonchus cause disease after July so not a concern

Turn out onto pasture not grazed in the past 2 years if possible
If not possible treat with Benzamidazoles q 15 days until finishing
Perform FEC every 3-4 weeks
- diclazuril and toltrazuril if necessary

Question 18

Devise a worming strategy for store lambs on pasture summer to later Autumn and finished inside.

Answer 18

Risk:
Telodorsagia, haemonchus, fasciola, Trichostrongylus
Nematodirus can occasionally cause disease in Autumn too

Turn out onto clean pasture where possible
Try to use home bred stores
Quarantine any bought in stores
- treat with monapantel / derquantel for roundworms
- triclabendazole for fluke
Perform FEC every 3-4w

If nematode risk…
Treat with ivermectin q 5w (PPP 3w + 2w RA)
Treat with moxidectin q 6w (PPP 3w + 2w)
Treat with Benzamidazoles q3w

If fluke risk…
Treat with triclabendazole at housing
Treat with closantel in January
Treat with Albendazole in spring

Question 19

How should you treat nematodes in hill flocks?

Answer 19

Treat when they are handled
Moxidectin? Good and long acting
Ivermectin - RA and no resistance in N.battus
Triclabendazole Autumn, closantel January, Albendazole March

Question 20

What is a good quarantine worming strategy for sheep?

Answer 20

Monapantel or derquantel and abamectin - nematodes
Triclabendazole - fluke
Closantel in 7w and again in another 7w - fluke
Moxidectin/ doramectin - sheep scab

Hold off pasture for 24-48h
Then return to the contaminated pasture

Question 21

When should you dose the ewe?

Answer 21

48h before turn out - moxidectin / ivermectin
- reduces pasture contamination for lambs

Only treat - thin sheep, triplet bearing ewes, shearlings

Question 22

How does acute fasciolosis present?

Answer 22

Sudden death, anaemia, dysponea, pale

Disease in September - December
2-6 weeks after ingestion

Question 23

How does subacute fasciolosis present?

Answer 23

Late autumn onwards

Haemorrhagic anaemia 
Hypoalbuminaemia 
Weight loss
Enlarged liver 
Oedema
Blacks disease - Clostridium novyi

Question 24

How does chronic fasciolosis present?

Answer 24

January to March - 4-5 months post infection due to adults in the bile ducts

Hepatic fibrosis
Hypoalbuminaemia 
Anaemia
Weight loss
Sub mandibular oedema

Question 25

How can you diagnose fasciola hepatica?

Answer 25

History and CS
FEC - only positive 12w post-infection
Abattoir returns - migration tracts or adults in bile duct
PME
Haematology
Elevated liver enzymes - 13 day post infection
ELISA - 3w post infection
Coproantigen for fluke - 8-10w post-infection

Question 26

What dosing strategy for fluke should be used for an aver all rainfall in a known fluke area?

Answer 26

October (bought in for housing) - triclabendazole (acute)
January - closantel (subacute and chronic)
April - Albendazole (chronic)

Question 27

What additional dosing should be used on high risk farms during high risk years?

Answer 27

November - triclabendazole

June - triclabendazole (winter infection of snails)