Ostertagiosis and Trichostrongylosis - Sheep

Ostertagiosis and Trichostrongylosis

Parasites

Ostertagia species (abomasum) are responsible for outbreaks of clinical ostertagiosis in lambs; different species are found in sheep and cattle, but the life-cycle and pathogenesis are very similar. Trichostrongylus species found in the abomasum and small intestine also contribute to or may even cause ovine PGE.

Forms of Ovine Ostertagiosis and Trichostrongylosis

Type 1 Ostertagiosis (the predominant from of PGE in sheep)

• Mainly caused by O. circumcincta
• Affects lambs during first grazing season (July - September)
• Clinical signs
  • Diarrhoea
  • Weight loss
  • Reduced appetite

Type 2 Ostertagiosis

• Affects lambs >1 year old after first grazing season (January - May)
• Clinical signs
  • Progressive weight loss
  • Intermittent diarrhoea

Trichostrongylosis

• Caused by Trichostrongylus axei (abomasum) and Trichostrongylus species (small intestine)
• Affects lambs <1 year old towards the end of the first grazing season (November - December)
• Clinical signs
  • Dark foul-smelling diarrhoea ("black scour")
  • Weight loss

Epidemiology of Ovine Ostertagiosis - Periparturient Relaxation in Immunity (PPRI)

• Affects mainly breeding ewes but can also affect non-breeding animals (barren ewes and rams)
• Impaired immunity because of:

1. PPRI (breeding ewes only)
2. Poor plane of nutrition
3. Management (winter housing reduces antigenic stimulation)

• Increased worm egg output because:

1. Increased establishment of L3
2. Increased egg production per female worm
3. Resumed development of arrested larvae

Epidemiology of Ovine Ostertagiosis on clean and contaminated pasture

Clean Pasture

• EE: Ewes' periparturient ("spring") rise in faecal egg count
• AP: Autoinfection peak in L3, from (EE)
• LE: Lamb faecal egg count, from (AP); and
• AP2: Second peak in L3, from (LE)

Contaminated Pasture

• OW: Overwintered L3 on pasture
• EE: Ewes' periparturient ("spring") rise in faecal egg count
• LE: Lamb faecal egg count, from (OW) (no disease)
• AP: Autoinfection peak in L3, from (EE) and (LE)
• LE2: Lamb faecal egg count, from (AP); and
• AP2: Second peak in L3, from (LE2)

Diagnosis of Ovine Ostertagiosis and Trichostrongylosis

• Clinical signs
• Season
• Faecal egg count:
  • High in Type 1 ostertagiosis and trichostrongylosis
  • Variable in Type 2 ostertagiosis
• Blood pepsinogen:
  • Elevated in ostertagiosis only, unless large Trichostrongylus axei burden
• Post-mortem examination:
  • Ostertagiosis:
    • Hyperplastic nodules
    • Raised gastric pH
    • >10,000 adult worms
    • Large numbers of arrested larvae (Type 2 disease only)
  • Trichostrongylosis:
    • Severe enteritis
    • >30,000 adult worms

Control of Ostertagiosis (and Trichostrongylosis)

Clean Pasture

• Source of infection; ewes only
  • Dose ewes around lambing
  • Turn ewes and lambs out onto clean grazing

Contaminated Pasture

• Source of infection; ewes and lambs
  • Dose ewes around lambing (BUT won't prevent reinfection; use medicated feed blocks or intra-ruminal boluses)
  • Dose lambs at weaning and move to clean grazing

NOTE: If no alternative grazing available = dose lambs at weaning and repeat on two or three occasions at monthly intervals