Difference between revisions of "Ostertagiosis and Trichostrongylosis - Sheep"

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==Ostertagiosis and Trichostrongylosis==
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== Introduction ==
 
  
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''[[Ostertagia]]'' species are nemotodes that inhabit the abomasum and 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. ''[[:Category:Trichostrongyloidea|Trichostrongylus'' species]] are found in the abomasum and small intestine too also contribute to or may even cause ovine [[Parasitic Gastroenteritis|PGE]].  
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==== Parasites ====
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''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 [[Parasitic Gastroenteritis|PGE]].
  
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'''Type 1 Ostertagiosis''' (the predominant form of PGE in sheep) is mainly caused by ''O. circumcincta. ''It affects lambs during their first grazing season ('''July - September'''). '''Type 2 Ostertagiosis '''affects lambs >1 year old after first grazing season ('''January - May'''). '''Trichostrongylosis '''is caused by ''[[Trichostrongylus axei]]'' (abomasum) and ''Trichostrongylus'' species (small intestine) and affects lambs <1 year old towards the end of the first grazing season ('''November - December''').
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==== Forms of Ovine Ostertagiosis and Trichostrongylosis ====
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'''Type 1 Ostertagiosis''' (the predominant from of PGE in sheep)
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*Mainly caused by ''O. circumcincta''
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*Affects lambs during first grazing season ('''July - September''')
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*Clinical signs
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**Diarrhoea
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**Weight loss
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**Reduced appetite
  
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There is impaired immunity because of Periparturient Relaxation in Immunity (PPRI) (breeding ewes only), a poor plane of nutrition or management (winter housing reduces antigenic stimulation). This means there will be an increased worm egg output because of increased establishment of L3, increased egg production per female worm and resumed development of arrested larvae.
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'''Type 2 Ostertagiosis'''
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*Affects lambs >1 year old after first grazing season ('''January - May''')
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*Clinical signs
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**Progressive weight loss
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**Intermittent diarrhoea
  
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If the pasture is 'clean' then there will be a periparturient (spring) rise in faceal egg counts in ewes, which will cause an autoinfection peak in L3 and therefore an increased lamb faecal egg count. This will then cause a larger, second peak of L3 on pasture. If the pasture is 'contaminated', then there will be overwintered L3 on pasture. This will be followed by the ewe's periparturient rise in faecal egg count and the lamb's rise in faecal egg count from overwintered larvae. As before, an autoinfection peak will then occur of L3 on pasture and lamb faecal egg count will increase, followed by another peak in L3 on pasture. This indicates that if the pasture is contaminated, it makes little difference to lamb egg burden, due to the effect of the ewes on L3 numbers.
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'''Trichostrongylosis'''
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*Caused by ''Trichostrongylus axei'' (abomasum) and ''Trichostrongylus'' species (small intestine)
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*Affects lambs <1 year old towards the end of the first grazing season ('''November - December''')
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*Clinical signs
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**Dark foul-smelling diarrhoea ("black scour")
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**Weight loss
  
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==== Epidemiology of Ovine Ostertagiosis - Periparturient Relaxation in Immunity (PPRI) ====
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*Affects mainly breeding ewes but can also affect non-breeding animals (barren ewes and rams)
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*Impaired immunity because of:
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#PPRI (breeding ewes only)
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#Poor plane of nutrition
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#Management (winter housing reduces antigenic stimulation)
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*Increased worm egg output because:
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#Increased establishment of L3
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#Increased egg production per female worm
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#Resumed development of arrested larvae
  
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== Clinical Signs ==
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==== Epidemiology of Ovine Ostertagiosis on clean and contaminated pasture ====
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'''Clean Pasture'''
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*'''EE''': Ewes' periparturient ("spring") rise in faecal egg count
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*'''AP''': Autoinfection peak in L3, from (EE)
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*'''LE''': Lamb faecal egg count, from (AP); and
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*'''AP2''': Second peak in L3, from (LE)
  
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In Type 1 Ostertagiosis the most common clinical signs include diarrhoea, weight loss and a reduced appetite. In the type 2 disease, there may be progressive weight loss and intermittent diarrhoea. In Trichostrongylosis, there will be a dark, foul-smelling diarrhoea ("black scour") and weight loss, which are quite characteristic symptoms of the condition.
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'''Contaminated Pasture'''
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*'''OW''': Overwintered L3 on pasture
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*'''EE''': Ewes' periparturient ("spring") rise in faecal egg count
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*'''LE''': Lamb faecal egg count, from (OW) (no disease)
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*'''AP''': Autoinfection peak in L3, from (EE) and (LE)
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*'''LE2''': Lamb faecal egg count, from (AP); and
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*'''AP2''': Second peak in L3, from (LE2)
  
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==== Diagnosis of Ovine Ostertagiosis and Trichostrongylosis ====
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*Clinical signs
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*Season
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*Faecal egg count:
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**High in Type 1 ostertagiosis and trichostrongylosis
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**Variable in Type 2 ostertagiosis
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*Blood pepsinogen:
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**Elevated in ostertagiosis only, unless large ''Trichostrongylus axei'' burden
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*Post-mortem examination:
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**Ostertagiosis:
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***Hyperplastic nodules
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***Raised gastric pH
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***>10,000 adult worms
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***Large numbers of arrested larvae (Type 2 disease only)
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**Trichostrongylosis:
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***Severe enteritis
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***>30,000 adult worms
  
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== Diagnosis ==
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=== Control of Ostertagiosis (and Trichostrongylosis) ===
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'''Clean Pasture'''
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*Source of infection; ewes only
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**Dose ewes around lambing
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**Turn ewes and lambs out onto clean grazing
  
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The clinical signs plus the season are enough to make a preliminary diagnosis. A faecal egg count should be performed. Results will mostly show high numbers of both ''Ostertagia'' and ''Trichostrongylus''. However, in type 2 ostertagiosis, the numbers of eggs will be variable.
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'''Contaminated Pasture'''
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*Source of infection; ewes and lambs
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**Dose ewes around lambing (BUT won't prevent reinfection; use medicated feed blocks or intra-ruminal boluses)
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**Dose lambs at weaning and move to clean grazing
  
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Bloods should be taken and blood pepsinogen levels measured. This will be elevated in ostertagiosis only, unless there is a large ''Trichostrongylus axei'' burden.
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'''NOTE''': If '''no''' alternative grazing available = dose lambs at weaning and repeat on two or three occasions at monthly intervals
  
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If a post mortem examination is performed on an animal that has died of the condition, one will see hyperplastic nodules and a raised gastric pH in the case of Ostertagiosis. There will also often be >10,000 adult worms. In the type 2 disease there will also be a large number of arrested larvae present too. If the sheep died of ''Trichostrongylus'' infection, there will be a presence of severe enteritis on post mortem and over 30,000 adult worms can be seen.
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[[Category:Trichostrongyloidea]]
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[[Category:Sheep_Nematodes]]
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== Treatment and Control ==
 
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On a '''clean pasture''', the only source of infection are the ewes. So protocol is to dose ewes around lambing, then turn ewes and lambs out onto clean grazing. On '''contaminated pasture, '''ewes and lambs are the source of infection, so still dose ewes around lambing (BUT won't prevent reinfection; use medicated feed blocks or intra-ruminal boluses) and then 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.
 
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Treatment if there is an outbreak of the disease, is anthelmintic drenching and supportive care should diarrhoea be severe enough to warrant this.
 
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{{Learning
 
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|flashcards = [[Small Ruminant Nematodes Flashcards|Small Ruminant Nematodes Flashcards]]
 
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}}
 
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== References ==
 
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Blood, D.C. and Studdert, V. P. (1999) '''Saunders Comprehensive Veterinary Dictionary''' (2nd Edition) ''Elsevier Science''
 
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Fox, M and Jacobs, D. (2007) '''Parasitology Study Guide Part 2: Helminths '''''Royal Veterinary College''
 
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Merck &amp; Co (2008) '''The Merck Veterinary Manual '''(Eighth Edition)'' Merial''
 
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Radostits, O.M, Arundel, J.H, and Gay, C.C. (2000) '''Veterinary Medicine: a textbook of the diseases of cattle, sheep, pigs, goats and horses '''''Elsevier Health Sciences''
 
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{{review}}
 
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{{OpenPages}}
 
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[[Category:Gastric_Diseases_-_Sheep]] [[Category:Expert_Review - Farm Animal]]
 

Revision as of 22:12, 21 April 2010

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

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