Lecture 2 -- Nematodes of Sheep

Which endoparasites are found in the abomasum of ruminants?

• Teladorsagia circumcincta

• Trichostrongylus axei

• Haemonchus contortus

Which endoparasites are found in the small intestine of ruminants?

• Bunostomum spp.

• Nematodirus spp.

• Cooperia spp.

• Trichostrongylus spp.

Which endoparasites are found in the large intestine of ruminants?

• Oesophagostomum spp.

• Chabertia ovina

• Trichuris ovis

Which endoparasites have a similar trichostrongyle-type life cycle?

• Trichostrongylus spp

• Teladorsagia circumcincta

• Cooperia spp

Describe the life cycle of typical trichostrongyle life cycle.

Step 1: Adult male and female parasites live in the GI tract of the sheep (abomasum or small intestine) and mate.

Step 2: Only the fertilised female produces and lays eggs → Eggs pass through intestinal lumen and are excreted in faeces

Step 3: Eggs develop in faecal pat → L1 hatches 孵出 and feeds on bacteria in faecal pat → Grows to L2 → Moults to L3, which is ensheathed

Step 4: L3 released from the faecal pat by rain splash (L3 is the infective stage, found on grass)

Step 5: When the sheep is grazing the pasture, it picks up the L3 larvae and ingests the infected larvae

Step 6: Depending on what species that parasite is, it either goes to the abomasum or small intestine → It will most to L4 inside the host and matures as L5

What is the pre-patent period (PPP)?

Period of time from ingestion of infective L3 from the pasture to the detection of eggs in the faeces

E.g. If we have naive lambs that had never grazed an infected pasture and we put those naive lambs out, by day 21, all of them would be shedding eggs because they would all have a patent infection

What is a patent infection?

An infection where adult parasites are producing eggs and one be detected (e.g. by faecal egg count)

How long is the pre-patent period (PPP) for PGE nematodes?

~ 3 weeks

What is hypobiosis?

Arrested development of early L4 larvae within the host

• Those infective L3 larvae are ingested and penetrate the abomasal mucosa, where they develop into early L4 larvae

• BUT they then pause their development and remain dormant for several month

• When spring arrives and the temp. increases, the arrested larvae resume development, mature into adult females and males, and mate

What triggers hypobiosis?

Decreasing ambient temperature in autumn

P.S. If the winter is not cold enough, hypobiosis might not occur

Which parasites are shown in this picture?

Teladorsagia circumcinta

What are the key morphological features of adult Teladorsagia circumcincta?

• 1cm in length

• Both sex:

  • Fine cervical papillae at the head

• Males:

  • Symmetrical bursa and spicules at the tail end

  • Spicules can retract/ extend through bursa

Describe the life cycle of Teladorsagia circumcincta in the sheep abomasum.

Step 1: Ingestion of L3

• Sheep eat infective L3 larvae while grazing.

Step 2: Exsheathment and penetration

• L3 Swallowed and reaches the abomasum → After L3 is swallowed, L3 lose their protective sheath and penetrate the abomasal mucosa and burrows into gastric glands

Step 3: Larval development:

• Within the gastric glands, L3 moult to L4 and then L5.

Step 4: Emergence

• L5 (immature adults) emerge from the gastric glands into the abomasal lumen

Step 5: Maturation

• L5 develop into adults, mate, and fertilised females lay eggs in the lumen, which are passed out in the faeces.

How many Teladorsagia circumcincta larvae are needed to cause parasitic gastroenteritis in sheep?

At least 40,000 larvae.

How do Teladorsagia circumcincta larvae cause disease in sheep?

L4 and L5 develop in gastric glands → Damage glands → Parietal cells replaced by undifferentiated epithelial cells → Consequences:

• ↓ Acid production = ↑ Abomasal pH → Loss of bacteriostatic effect

• No conversion of pepsinogen to pepsin

• ↑ Mucosal permeability = Lose the tight junction between cell → “leaky” abomasum → Diarrhoea

What are the key morphological features of adult Trichostrongylus?

• Very small, hair like worms (4-7mm)

  • Smallest gastrointestinal nematodes in sheep

• Excretory pore at head end of the worm

• Female:

  • NO vulval flap

  • <12 eggs uterus can be seen in the uterus

• Male:

  • Bursa present

  • Short, unequal and dissimilar spicules

How do Trichostrongylus spp. larvae cause disease?

L4 and L5 develop deep in sub-mucosa and mucosa → Form sub-epithelial tunnels → Cause villous atrophy, haemorrhage, oedema because of protein loss, and diarrhoea (black scour)

What are the clinical signs of Trichostrongylus infection in lambs?

• Black scour

• Weight loss/ poor weight gain

• Poor skeletal growth

When does Trichostrongylus disease typically occur?

Autumn

Which animals are commonly infected by Cooperia spp.?

Cattle and sheep

What are the key morphological features of adult Cooperia spp.?

• Presence of cephalic vesicle = Cuticular inflation on the head end

• Striation on the head

• Body coiled in the middle of its body = “Watch-spring”appearance

• Male:

  • Short, stumpy spicules

How pathogenic is Cooperia spp.?

Usually mild, but heavy infections can cause disease.

What are the pathological effects of heavy Cooperia spp. infections?

• Reduced weight gain

• Catarrhal enteritis

• Villous atrophy

• Oedema of the intestinal mucosa

Which parasites are shown in this picture, and which morphological feature supports this conclusion?

Teladorsagia circumcincta (Male)

• Symmetrical bursa and spicules

Which parasites are shown in this picture, and which morphological feature supports this conclusion?

Teladorsagia circumcincta (Both sex)

• Cervical papillae at head end

Which parasites are shown in this picture, and which morphological feature supports this conclusion?

Trichostronglyus spp.

• Excretory notch

Which parasites are shown in this picture, and which morphological feature supports this conclusion?

Cooperia spp.

• Presence of cephalic vesicle and cervical vesicle

• Cervical vesicle (Inflated but not bubble like)

• Striation on the head

Which parasites are shown in this picture, and which morphological feature supports this conclusion?

Cooperia spp.

• Coiled body (= “Watch spring” worm)

Which parasites are shown in this picture, and which morphological feature supports this conclusion?

Coopria spp. (Male)

• Short, stumpy spicules

What are the differences between type 1 and type 2 PGE?

Type 1 PGE:

• First season grazing lambs = Lambs that have never been grazed

• Happen in the mid summer

Type 2 PGE:

• Caused by hypobiosed larvae → Simultaneous emergence of L5

• Happen in late winter/ early spring because of the increased temp

What are the clinical sings of PGE (Both type 1 and type 2)?

• Profuse watery diarrhoea

• Weight loss

• Inappetence

• Dehydration

• Poor weight gain

  • Reduced appetite

  • Reduced feed intake

  • Loss of plasma proteins into gastro-intestinal tract

• Death