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Parasitic Gastroenteritis (view source)
Revision as of 16:27, 26 December 2008
, 16:27, 26 December 2008→Rate of Infection
*if infected stock grazed pasture previous year
*if infected stock grazed pasture previous year
*longer lifespan in colder weather
*longer lifespan in colder weather
b) ''Larval numbers decline in the spring'':
b) ''Larval numbers decline in the spring'':
*stock ingest remaining overwintered L3
*stock ingest remaining overwintered L3
*strongyle eggs passed out with faeces onto pasture
*strongyle eggs passed out with faeces onto pasture
c) ''Development from egg to L3'':
c) ''Development from egg to L3'':
*development is therefore influenced largely by '''macroclimate''' and '''temperature'''. Net result = concertina effect.
*development is therefore influenced largely by '''macroclimate''' and '''temperature'''. Net result = concertina effect.
d) ''Translation of infective larvae''
d) ''Translation of infective larvae'':
*movement of larvae from dungpat onto grass in order to infect final host
*movement of larvae from dungpat onto grass in order to infect final host
*L3 must cross a zone of repugnance around the dungpat (up to 45cm) - normally left ungrazed
*L3 must cross a zone of repugnance around the dungpat (up to 45cm) - normally left ungrazed
*L3 cross zone by swimming in a film of moisture. Also, beetle and earthworm activity, rain splash, soil migration, etc.
*L3 cross zone by swimming in a film of moisture. Also, beetle and earthworm activity, rain splash, soil migration, etc.
e) ''Autoinfection peak in infective larvae'':
*due to larvae reaching L3 stage simultaneously ("concertina" effect) and translation of L3 onto pasture
*factors affecting either egg - L3 development or translation will influence the timing of the peak, e.g. cold spring, dry summer
*decline in L3 after autoinfection peak due to a combination of (a) shorter lifespan in warmer weather; and (b) autumn flush of grass growth
f) ''Overwintering of larvae'':
In temperate climates, some species can overwinter on the grass, while others cannot. In either case, nematodes may survive inside the host for long periods of time, not as normally developing adult worms (that would be expelled within a few weeks), but as larval worms that have become temporarily arrested in their development and may remain inside the host 'asleep' for many months.