CSIRO Livestock Industries

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CSIRO Livestock Industries
Interspecific Parasite Interactions Agent-Based
Modelling
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Why are interactions important?
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How may parasites interact?

• Direct interactions
• competition for a resource
• toxic / non-toxic excretions

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How may parasites interact?

• Indirect interactions
• Alteration of host environment
• Host immune response

Host Immunity
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Evidence from a wild host
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Evidence from a wild host
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Simple Model
-ve
-/ve
ve

• Interactions may increase / decrease the
  efficacy of vaccine
• May cause unexpected increases in previously
  benign species

Lello, Boag, Fenton, Stevenson Hudson (2004)
Competition and mutualism among the gut helminths
of a mammalian host. Nature 22nd April
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CSS Research Team

• CSIRO Collaborators
• Sue McClure Immunology
• Peter Hunt Molecular identification of larvae
  
• Robert Dobson Parasitology and modelling
• International Collaborators
• Andrew Fenton Mathematical modelling
• (University of Cambridge)
• Mark Viney Parasites and immune interactions
• (University of Bristol)

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The Original Model
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The Advanced Model
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Preliminary Results
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Experimental Protocols in Sheep

• 70 sheep currently infected with
• Haemonchus contortus
• Trichostrongylus colubriformis
• Ostertagia circumcincta
• H. c. with T. c.
• H. c. with O.c.
• T. c. with O. c.
• H.c with T.c. and O.c.
• 10 week infection
• FEC and larval differential carried out weekly
• Immune parameters monitored
• Final cull
• full worm count
• tissue samples for immune response
• measurements

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Sheep Helminth Interactions What we knew!

• In Host
• Ostertagia circumcincta displaces Haemonchus
  contortus (change in abomasal pH cross
  immunity)
• In Faeces
• H. contortus suppresses development of
  Trichostrongylus vitrinus
• T. vitrinus suppresses development of T.
  colubriformis
• T. colubriformis and H. contortus no effect
• In Field
• H. contortus controlled and T. vitrinus appears

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Sheep Helminth Interactions Preliminary Results

• Is egg output affected by interspecific
  interactions?
• Species Egg Output / g diff combined FEC
  / g
• H. contortus suppressed by O. Circumcincta
• O. circumcinta suppressed by both H. contortus
  and T. colubriformis
• T. colubriformis not affected

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Haemonchus contortus egg output in single and
mixed infections
10000
1000
97 to 99 reduction
Egg Output
100
10
1
H.c.
H.c. with T.c.
H.c. with O.c.
Hc with T.c. O.c.
Group
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Ostertagia circumcincta egg output in single and
mixed infections
1000
100
93 to 99 reduction
Log Egg Output
10
1
0.1
O.c.
O.c. with H.c.
O.c. with T.c.
O.c. with T.c. H.c.
Group
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Sheep Helminth Interactions Preliminary Results

• Is adult worm burden affected by interspecific
  interactions?
• H. contortus suppressed by O. circumcincta only
• No significant effects of other species on O.
  circumcincta or T. colubriformis

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Haemonchus contortus adult numbers in single and
mixed infections
66 to 73 reduction
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THANKS!

• Andrew Fenton University of Cambridge and
  London Zoological Society
• Peter Hudson Penn State University
• Ian Stevenson Sunadal Data Solutions
• Rachel Norman University of Stirling

Brian Boag for data, rabbit knowledge and a lot
of support
Malcolm Knox CSIRO Livestock Industries Kerri
Tyrrell CSIRO Livestock Industries Debbie
Hickey CSIRO Livestock Industries Fiona
MacArthur CSIRO Livestock Industries Peter
Bradley CSIRO Livestock Industries
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