L1 Transmission Flashcards
4 types of transmission
Simple/direct - 1 host in lifecycle
Complex - >1 host, intermediate host
Free living stages - eg Helminth eggs, infective larvae
Host/host - filarial nematode microfilarae/L3s, Tapeworm plero and proceriods
3 features of free living infective stages
Large numbers to maximise chance f successful transmission
Environmentally resistant
Targeted for new host, behavioural adaptation to enhance chance of finding host
Describe Ascaris transmission strategy
Strategy is to heavily contaminate environment - 2000 eggs per worm per day.
Eggs not infective, requires time external to host to become infective.
Temp dependent process, springtime infective - when there are more susceptible piglets.
Describe Hookworm transmission strategy
L3 larvae infective
Behavior is to move away from faeces to higher CO2 conc and warmth.
5000-15000 eggs per day
How did parasitism evolve in nematodes
Appears to have evolved many times
Many free living nematodes have resistant larval form and can arrest development.
L3 stage infective in animal parasitic nematodes. non feeding, arrest the continue development when conditions improve.
Entomopathogenic nematodes could be a mode of parasitism evolution.
Entomopathogenic nematodes -
eg Steinemema, Heterorhabiditis.
Infective larvae carry specialised bacteria.
Bacteria released in host, and kill host.
Worms feed on bacterial soup and multiply.
Infective larvae released from dead hosts.
Maybe suggest how parasitism evolved?
Describe transmission of filarial worms - Onchocerca and Wuchereria.
insect transmitted
L1 W. microfilariae circulate in blood, or in skin, O.
In vector develop to L3 stage and transmitted to mammalian host.
Describe how a circadian rhythm can help parasites.
Microfilariae of W. bancrofti. In day - concentrated in capillaries of lung. At night - peripheral blood.
Varies in location according to biting range, can vary geographically for same strain.
Uses cue of O2 gradient in lung capillaries.
Why is changing host in a complex lifecycle important?
Must change host to receive signal to continue development.
Often moult when change host, so can activate different genes/epigenetic processes to change morphology, physiology and biochemistry. Must have different biology as in different environment.
differences in environment between a mammalian and insect host?
Mammalian - 37 degrees, hot. high O2, vertebrate immune response, MF development blocked.
Insect - ambient temp, low O2, invert immune response, L3 development blocked.
How does Toxoplasma gondii promote transmission?
Can change behaviour of intermediate host eg rat.
Makes rat bolder so more likely to be preyed on by cat, allowing transmission.
Demonstrated by Berday et al 2000.
sheep selected for low and high FEC showed differences in behaviour. how?
R sheep - less grazing on tussocks, so less parasites
S sheep - higher FEC, altered behaviour to graze more on tussocks.
Less behavioural alteration of sheep with low FEC
