GIN and PGE

Gastro-intestinal nematodes and Parasitic gastro-enteritis

Why is the location of a gastrointestinal nematode important?

to identify the nematode and the pathology of the disease

Which 2 GINs are found only in the abomasum of the sheep?

teladorsagia circumcincta

trichostrongylus axei

Which GINs are found in the sheep small intestine?

cooperia species

trichostrongylus species

Which GINs are found in the sheep large intestine?

chabertia species

oesophagostomum species

Which location in the sheep GI tract is the least clinically significant for GINs?

large intestine - does not cause many problems

Which GINs are grouped under ‘typical trichostrongyles’?

telardorsagia circumcincta

cooperia species

trichostrongylus species

What is hypobiosis?

a temporary, genetically programmed arrested development of larvae within the host in response to a trigger received by the free-living L3

What is the ‘typical trichostrongyle’ life cycle?

1. adult worms in abomasum of host mate and produce eggs

2. eggs are shed in the faeces of the host

3. L1 and L2 both occur within the faeces, and larvae feed on bacteria in the faeces

4. during L3, larvae are separated from faecal matter and spread onto pasture by rain splash

5. L3 larvae are ingested by a new host (infective stage)

6. prepatent period lasts approx 3 weeks

7. larvae enter L4 and L5 in GI tract of host and then the cycle repeats once larvae are mature

During which stage of the ‘typical trichostrongyle’ lifecycle are the larvae free-living?

L1-L3

What are the features of trichostrongyle eggs?

thin wall

barrel shaped

undifferentiated - contain undeveloped morula

What is the prepatent period?

the time taken from the time of infection to the detection of eggs in the faeces

What is a patent infection?

an infection that can be detected

Where does hypobiosis occur?

inside the host

What is the primary species involved in parasitic gastroenteritis?

teladorsagia circumcincta

What stimulates larva to hyperbiose?

a drop in ambient temperature

What are the identifying features of adult teladorsagia circumcincta?

very common in temperate regions

approx 1 cm long

slender, pinky-brown worm

fine cervical papillae at the head end in both males and females

found in sheep abomasums

males have a bursa and spicules

How does teladorsagia circumcincta develop?

1. L3 larvae are swallowed by grazing sheep

2. larvae travel to abomasum and burrow into gastric glands

3. larvae develop to L4 and L5

4. L5 emerge into the lumen of the abomasum where they mature to adults

5. adult worms mate here and females lay eggs

What does hypobiosis allow to happen?

an accumulation of a large number of L4 larvae in the mucosa, as they are not developing and leaving the host

How is pathogenic gastroenteritis caused?

1. large numbers of developing teladorsagia circumcincta larvae accumulate and develop in the gastric glands of the host and damage the glands

2. parietal cells are replaced by undifferentiated epithelial cells (as cannot repair and replicate)

3. acid production is lost due to the loss of parietal cells

4. abomasum pH increases which prevents the bacteriostatic effect

5. pepsinogen is no longer converted to pepsin by acid

6. the permeability of mucosa increases

What are the clinical signs of type 1 PGE?

profuse watery diarrhoea

weight loss

inappetance

dehydration

death

What is the key sub-clinical sign of type 1 PGE?

poor weight gain due to reduced appetite/ feed intake and loss of plasma proteins into the GI tract

Which demographic most commonly develop type 1 PGE?

first season grazing lambs around mid-summer

What causes type 2 PGE?

simultaneous emergence of mature teladorsagia circumcincta after a period of hypobiosis which causes a sudden surge of the parasites in the abomasum

Which trichostrongylus species is not found in the small intestine?

t. axei

What is caused when trichostrongylus species are predominantly responsible for a PGE infection?

black scour

What are the identifying species of trichostrongylus species?

very small (4-7mm)

smallest of the GIN worms in the abomasum

excretory pore at the head end (appears as a notch in the cuticle) which is only found in this species

females have no vulval flap and very few eggs

How do you differentiate between male and female trychostrongylus worms?

males have bursa and short, unequal spicules

females have eggs

How do trychostrongylus species develop?

larvae develop deep in sub-epithelial tunnels in the mucosa

What do trychostrongylus cause when they emerge in the host?

villous atrophy

haemorrhage

oedema

diarrhoea

What does trichostrongylus disease cause?

weight loss/ poor weight gain

black scour

poor skeletal growth

When are cooperia species typically found?

in cattle and sheep

very common but not strongly pathogenic

What are the identifying features of cooperia species?

tightly coiled worm

cephalic vesicle (appears as inflation on head end)

male has short, stumpy spicules

What can heavy infections of cooperia cause?

catarrhal enteritis

villous atrophy

oedema of intestinal mucosa