Parasitology Flashcards
What are some questions you could ask yourself about veterinary parasitology?
- What is it?
- How did the animal get it?
- Could it have been prevented?
- Is it harmful?
- What can be done to get rid of it?
- What can be done to stop it coming back?
How do animals get an increased worm burden?
- Its rare for helminths to be able to complete their lifecycle without leaving the host… thus if an animal has more worms it must have been exposed to more infectious stages
What is host permissiveness?
Susceptibility
- The likelihood that parasites will establish patent infections in the host after exposure/contact
In non-permissive hosts, parasites… what?
- Fail to establish patency / are killed or hide in tissues (paratenic host)
- Establish only in small numbers
- Generally fail to affect host health
How does cross-grazing affect parasitism?
e.g. sheep and cattle in a paddock together
Uses non-permissive hosts to reduce infection
What age animals are usually the most permissive?
Young animals
- Immunologically naive
- There is no evidence that maternally derived antibodies provide any protection against helminths
- However very young animals aren’t usually eating much pasture
- May be infected by milk
What is age immunity?
When older animals can be harder to infect even if it is occurring for the first time
e.g. T.canis infects 3 week old pups but not 3 month old pups by HT route
What is acquired immunity?
Experience of infection allows immune system to develop
- Reduces host permissiveness
- Generally poor or slow to develop for helminths
- better for migratory GI and pulmonary species
- poor for LI species
- very poor for tissue dwelling helminths
How does browsing behaviour of herbivores affect their parasite burden?
Browsing animals generally have fewer nematode parasites than grazing animals
- they don’t eat where they poo!
What are some other host factors that can affect parasite burden?
Breed differences
Individual differences
Robustness/ resilience
Host response
Typical strongylid lifecycle….
Egg is a morula when laid
- L1 hatches from egg and feeds on bacteria to grow
- It enters lethargus
- It then moults to L2
- The infective stage is L3 which is still enclosed in L2 cuticle and is referred to as ensheathed [L3]
- After entry into the host by ingestion, exsheathment occurs
- Migratory strongylids start migrating after exsheathment and moult in organs they migrate through
- Most inhibit at L4 stage (allows them to survive harsh conditions)
Why is Nematodirus spp the exception of strongylids?
Develops into [L3] before hatching
- Larger egg - slow developing
What are the three things that drive nematode biology outside the host?
- Oxygen (poo pat)
- Moisture
- Temperature
What is the minimum temperature below which no activity/ development occurs?
5-10C
- Below this they will coil up and become quiescent
What happens when temperature is above 5-10C?
The rate of development starts to increase exponentially
- Higher temps mean the faster rates are offset by increased death
> 40-50C lethal quickly
What is the optimum temperature for nematode development?
25-27C
- high development rate and low mortality rate
- Eggs hatch in 24 hours
- [L3] reached in 6-7 days
Which type of faecal material has the best ability to retain moisture?
Dung pats > loose sheep pellets > diarrhoea
[L3] from which animals are less likely to develop or survive well?
- Eggs from older more immune sheep
- From resistant/ immune animals
