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Internal Parasites
& Lifecycles

Descriptions
Symptoms
Sheep

The lifecycle of a roundworm

Parasite lifecycle

Step 1 

All roundworms begin as eggs. These eggs are produced by female adult roundworms living in the gut of the animal. 

Step 2 

These eggs are passed out in the animal’s dung onto the ground. 

Step 3 

The eggs hatch into larvae, given the right environmental conditions (sufficient moisture levels and temperature). 

Step 4 

The larvae develop and become infective. They move up blades of grass in water droplets, where they can be eaten by grazing sheep. 

Step 5 

Once ingested, the larvae enter the gut of the animal and either develop into adults quickly, or they may stay in an “inhibited” stage until a later time (for example, during a summer drought or winter cold). 

When the external conditions are “right” (i.e. favourable for worm survival) all the inhibited larvae develop into adults. 

Introduction to Sheep Worm Monitoring

The table below offers a summary of the most important roundworms of sheep in Australia

Internal Parasite Site of Infection

Teladorsagia circumcinta

(Small brown stomach worm)

Absomasum

Haemonchus contortus

(Barber's pole worm)

Absomasum

Trichostrongylus spp.

(Black scour worm)

Small Intestine

Nematodirus spp.

(Thin-necked intestinal worm)

Small Intestine

Oesophagostomum spp.

(Nodule worm/Large bowel worm)

Large Intestine

Sheep Internal Parasites & Best Practice Worm Monitoring

Barbers Pole Worm

Haemonchus contortus

Parasite - Barbers Pole

What is it?

Barbers Pole is a round worm nematode

Resides in the abomasum (4th stomach) - burrow in and attach through the lancet on their head

The females have a banded (barber pole) colouration and can be 20mm to 30mm in length (males are pale pink and 15mm in length)

Each female can lay 10 000 eggs per day and an animal can have thousands of females feeding off it
These eggs are laid and passed with the faeces to hatch and develop to L3 larvae in 7 days

The ideal environmental conditions are warm moist spring, summer, and autumn seasons

The L4 larval stage can become inhibited from transitioning to adult stage and migrate into abomasal wall until seasonal conditions become more viable for egg laying

Widespread resistance to anthelmintic groups and even multi-combinational drenches

What are the Symptoms?

The females are blood feeders and can consume 0.05ml / day each

This can lead to anaemia, lethargy, weakness and death

Animals will show pale gums and pale eyelids

Sheep with good nutrition and with high condition scores can be affected, collapse and die but are more resilient than poorer condition score sheep

What does it mean for you?

Affects all sheep irrespective of condition score, age or breed

Clinical and Sub-clinical production losses

Death by anaemia

Loss of condition and depressed growth rates

Reduction in meat and wool production

Solutions & Next Steps

Drenching with an effective sheep drench
WEC to monitor egg output with larvae differentiation
Quarantine new sheep until potential risk is accessed
Recovery from a severe infection is slow and requires the provision of adequate nutrition

Black Scour Worm

Trichostrongylus spp.

Parasite - Black Scour

What is it?

Black scour worm is a round worm nematode

There are several species T. colubriformis, T.vitrinus, T. rugatus (arid regions) & T. axei (found in abomasum)

6-8mm in length and the L4 larvae burrow into the GI mucosa of the abomasum or small intestine to mature

Females produce 200 eggs per day
Causes diarrhoea, especially in young sheep

The ideal environmental conditions are in late summer and autumn

T. colubriformis occurs in the warmer summer rainfall areas while T. vitrinus occurs more frequently in winter rainfall areas

Widespread resistance to anthelmintic groups and even multi-combinational drenches

What are the Symptoms?

Black scour worm causes damage to villi of the small intestine

Symptoms include:
    • appetite loss
    • lethargy
    • malabsorption
    • scours (generally black in colour)
    • the malnutrition and dehydration effects may result in death

What does it mean for you?

Affects all sheep irrespective of condition score, age or breed

Clinical and Sub-clinical production losses

Death through scouring

Loss of condition and depressed growth rates

Reduction in meat and wool production

Solutions & Next Steps

Drenching with an effective sheep drench
WEC to monitor egg output with larvae differentiation
Quarantine new sheep until potential risk is accessed
Recovery from a severe infection is slow and requires the provision of adequate nutrition

Small Brown Stomach Worm

Teladorsagia circumcincta

Parasite - Small Brown

What is it?

Small Brown stomach worm is a round worm nematode

Small in size (8-12mm)

Resides in the abomasum (4th stomach) - causes lesions on the mucosal wall

Females can lay 100 eggs per day
Small brown stomach worm has a winter dominant lifecycle

Widespread resistance to anthelmintic groups and even multi-combinational drenches

What are the symptoms?

Small brown stomach worm causes inflammation to the mucosal wall

Interferes with digestion resulting in less metabolisable energy and protein available

Symptoms include:
    • scours
    • rapid weight loss
    • immune depletion
    • physical damage to the mucosa
    • anaemia, loss of plasma proteins
    • loss of appetite & milk suppression
    • death

What does this mean for you?

Affects all sheep irrespective of condition score, age or breed

Clinical and Sub-clinical production losses

Death through scouring and malnutrition

Rapid loss of condition and depressed growth rates

Reduction in meat and wool production

Solutions & Next Steps

Drenching with an effective sheep drench
WEC to monitor egg output with larvae differentiation
Quarantine new sheep until potential risk is accessed
Recovery from a severe infection is slow and requires the provision of adequate nutrition

Nodule Worm

Oesophagostomum columbianum

Nodule Worm

What is it?

Found in the Summer rainfall areas of Northern NSW and Southern Qld

Causes nodules predominantly in the large intestine and colon

Economic loss for sausage casings

What are the symptoms?

Soft faeces, may contain blood and have high levels of mucous

Unthrifty sheep

What does this mean for you?

Affects all sheep irrespective of condition score, age or breed

Clinical and Sub-clinical production losses

Death through scouring

Rapid loss of condition and depressed growth rates 

Reduction in meat and wool production

 

Solutions & next steps

Drenching with an effective sheep drench

WEC to monitor egg outlay with larvae differentiation

Quarantine new sheep until potential risk is accessed

Large mouthed bowel worm

Chabertia ovina

What is it?

Chews and damages the mucosal plugs of the intestinal lining

Causes thickening and haemorrhage of the intestinal lining

Winter rainfall distribution

The female worm lays 3,000-5,000 eggs/day

Occurs primarily in lambs

What are the Symptoms?

Soft faeces, may contain blood and have high levels of mucous

Unthrifty sheep

What does this mean for you?

Affects all sheep irrespective of condition score, age or breed

Clinical and Sub-clinical production losses

Death through scouring

Rapid loss of condition and depressed growth rates 

Reduction in meat and wool production

 

Solutions & next steps

Drenching with an effective sheep drench

WEC to monitor egg outlay with larvae differentiation

Quarantine new sheep until potential risk is accessed

Small intestinal worm (exacerbates mixed infections)

Cooperia spp

What is it?

6-9mm in size, often seen coiled up

Live in small intestine

Lay 1-400 eggs per day

What are the symptoms?

Increases the symptoms of mixed infections

What does this mean for you?

Affects all sheep irrespective of condition score, age or breed

Clinical and Sub-clinical production losses

Death through scouring

Rapid loss of condition and depressed growth rates 

Reduction in meat and wool production

 

Solutions & next steps

Drenching with an effective sheep drench

WEC to monitor egg outlay with larvae differentiation

Quarantine new sheep until potential risk is accessed

Thin-necked intestinal worm (primarily lambs)

Nematodirus spp

What is it?

Live in small intestine

Require frosts to trigger hatching

Large, hardy eggs (reside in the environment for months)

Larva develops within egg (50-100 eggs/day)

What are the symptoms?

Ill thrift, scours, dehydration

Death within 2-3 days

What does this mean for you?

Affects all sheep irrespective of condition score, age or breed

Clinical and Sub-clinical production losses

Death through scouring

Rapid loss of condition and depressed growth rates 

Reduction in meat and wool production

 

Solutions & next steps

Drenching with an effective sheep drench

WEC to monitor egg outlay with larvae differentiation

Quarantine new sheep until potential risk is accessed

Sheep Faecal Egg Count Sampling and Culturing

Further Reading

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