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16 Cards in this Set
- Front
- Back
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What main factor affects parasite transmission? |
Density |
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Theoretically, when are parasites most likely to regulate host populations during infection? |
When host mortality is low - death to host results in death of parasite
And host fecundity (reproducing abilities) is high - parasites can live longer (Overcompensation results in cycles) |
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What factors interfere with the ability to see the effect mortality and fecundity has on the parasite populations? |
Confounding factors - may be inherently important (e.g. increased density in soay sheep living on island with no predators) |
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Give an example where competition between host species is mediated by parasites.
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Parasites in pheasants has no effect on muscle mass, but does in partridges, reducing their competition |
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Generally speaking, how does parasite aggregation present itself? |
Few individuals hold much of parasite population |
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What does parasite aggregation result in? |
Regulation through fecundity, resulting in cycles. |
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Do macroparasites cause morbidity or mortality? |
Morbidity |
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Why are macroparasites overdispersed? |
Samples generally too small, with underestimation of mean number of parasites per cow. |
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What causes parasite aggregation? |
Clumping of infection doses (e.g. tick oviposition, nematode larvae around faeces) Heterogeneity in environment (uneven living conditions for free-living stages e.g. Faciola) Heterogeneity in host immune response (uniform would decrease aggregation) |
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What are the consequences of aggregation? |
Clinical parasitism detectable in some species - can be used for targeting treatment |
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Why is targeted selective treatment used? |
Treating only those with highest burden prevents resistance and leaves refugia to allow immunity |
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What are some indicators that targeted selective treatment should be used in a particular animal? |
Morbidity - Body condition, diarrhoea etc Immunological tests - Serum pepsinogen, antihelminth antibodies Parasitological - Faecal egg count, antigen detection Production - Weight, milk yield Also, behaviour, inflammatory and metabolic markers useful |
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How do you decide whether to use targeted selective treatment for nematode burdens in particular horses? |
Individual FEC, mark at 200 eggs per gram Or serial subsampling (groups of 3-5) |
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Is there a predisposition pattern for nematode infection in horses? |
Yes - Previously high eggs shedders tend to get reinfected |
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Why must care be taken in autumn in terms of worm burdens in horses? |
Encysted cythostomins |
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How do you decide whether to use targeted selective treatment for nematode burdens in particular sheep? |
FEC FAMACHA (Haemonchus) Diarrhoea (dag) score Body condition Weight gain Farmer's judgement (Random 'selective' treatment) |
