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Host-parasite interactions 3
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- 1What is aggregation?Over dispersion
- 2Give an example of a parasite that causes cycles in the re grouse population.Trichostrongylus tenuis
- Population cycle of red grouse driven by worms, when worming implemented there was no drop in population - 3What are the theoretical prediction of parasites on the effect of host populations?1. Parasite transmission is density-dependent, so parasites can potentially regulate host populations
2. Parasites are most likely to regulate host populations if:
- Effect is on host mortality is low
- Effect on host fecundity is high
3. Time delays in effects on individual hosts will tend to lead to cycles, through overcompensation - 4What is fecundity?Production of offspring
- 5Why will a parasite have more control on population if host mortality is low and fecundity is high?If mortality was high, then less chance for the parasite to reproduce and have an effect - end up killing themselves quicker
- 6How do parasites normally have an effect?High density = increase transmission = increase parasite population
- 7What happens to parasites in normal systems?- Effects on host mortality or fecundity are necessary but not sufficient to prove regulation
- Confounding factors are very common
- So they need to be removed to have a clear view
- But they might be inherently important to the system - 8What are parasites important for?Stability of grazing systems
- Integral to ecosystems - 9What is the affect of parasites on the pheasant and partridge populations?Pheasants propagate parasites life cycle so that the partridges are out-competed and excluded
- 10Is parasite aggregation universal?Yes - non random distribution among hosts
- 11What is the general aggregation for parasites in the host?A few individuals carry the majority of the parasite
- 12What does most parasites being concentrated in a few hosts lead to?- Favour regulation through host fecundity which leads to cycles
- 13What are macroparasites generally?1. Cause morbidity rather than mortality
2. Are highly overdispersed
3. Are underestimated - 14Why are macroparasites underestimated?1. Subclinical infection so nothing obvious
2. Really common to have worms
3. Aggregation leads to underestimation due to systematic underestimation of mean - due to small sample size - 15How can systematic underestimation of the mean be avoided?Need a higher amount of sample so 10-15
- 16What are the 3 mechanisms of aggregation?1. Accumulation of random infection events
- clumping of infection doses
2. Heterogeneity in the environment
- uneven conditions for free-living stages
3. Heterogeneity in the host immune response
- uniform response will decrease aggregation - 17What are the consequences of aggregation?1. Detection of clinical parasitism
2. Sampling a group of animals
3. Target treatment - 18What is TST?Targeted Selective Treatment
- 19When is targeted selective treatment used?To find the individuals that are producing the majority of the eggs
Overdispersion: 80:20 or Pareto rule - 20Give 5 ways in which we can find markers of helminth infection.1. Morbidity: diarrhoea score, dig score, body condition, FAMACHA
2. Immunological/biochemical: Serum pepsinogen, anti-helminth antibodies, liver and bile duct enzymes
3. Potentially useful markers: metabolic markers, inflammatory markers, animal behaviour
4. Parasitological: faecal egg count, helminth-specific antigen or DNA
5. Production: weight gain, milk yield, wool growth/quality, carcass weight/quality - 21How should you TST for nematodes in horses?1. FEC individual counts for horses
2. Predisposition: tendency to be repeated high or low shedders
3. Large yards - serial subsampling
4. On farm of suitably qualified person
5. Care in autumn: encysted cytothostomins - 22What TST for nematodes in sheep?1. FEC
2. FAMACHA: for Haemonchus
3. Diarrhoea / dag score
4. Body condition
5. Weight gain
-automated systems
-tie in to general flock management
6. 'Farmer's eye'
7. Random 'selective' treatment - 23What are 3 main points about aggregation?1. Underpins regulatory effects of parasites
2. Complicates sampling of parasites in a group of hosts (higher sample size)
3. Provides an opportunity to target highly infected individuals - 24What differs with TST in different systems?The indicators used
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- BVSc (Parasitology EM) 2. Agents of disease AD1 Fichas sobre Host-parasite interactions 3, creado por Rachael Jones el 27/02/2017.
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