Ecology of the free-living stages of major trichostrongylid parasites of sheep

Grazing systems and worm control in sheep: a long-term case study involving three management systems with analysis of factors influencing faecal worm egg count

“…On the second point relating to larval die-off between grazing periods, the factors affecting survival of L 3 on pasture have been reviewed by O'Connor et al (2006). The ensheathed infective L 3 is the stage of the lifecycle most resistant to adverse environmental influences but, as the L 3 cannot feed, survival is reduced by factors that increase motility or metabolic rate, and thus deplete metabolic reserves, such as rainfall and elevated temperatures.…”

“…On farmlet C, rest periods were rarely below 50 days and sometimes over 150 days, with a mean of 98 days (Table 3) thus allowing time for significant larval die-off in most cases. It should be noted that, in practice, these spelling times will overestimate the decrease in larval populations on pasture as L 3 may continue to develop and appear on pasture for several weeks following removal of stock, particularly in the case of T. colubriformis and T. circumcincta (O'Connor et al 2006). The improved level of control of worms on farmlet C was associated with significantly increased susceptibility to worm infection (Colvin et al 2012) and reduced animal productivity as shown by reduced liveweights (Hinch et al 2013a) and fat scores (Hinch et al 2013b) of livestock on this farmlet relative to those on farmlets A and B.…”

“…On the other hand, the susceptibility of H. contortus eggs to desiccation and low temperatures is likely to make them just as susceptible to rapid rotational grazing as they would be under tropical conditions, but probably for different reasons. Temperature and moisture are often limiting in the Northern Tablelands for development of H. contortus eggs to L 3 (O'Connor et al 2006(O'Connor et al , 2007, and failure of development is likely to be a major mechanism operating in this environment. The superior ability of Trichostrongylus and Teladorsagia species to survive in the embryonated egg stage during cool dry conditions relative to Haemonchus could account for the species difference in response to IRG observed in this experiment.…”

Animal health aspects of adaptation to climate change: beating the heat and parasites in a warming Europe

“…The latter are voided onto pasture as eggs and need to undergo a period of development, to the infective stage larvae, at pasture. The dependence of the developmental success and survival of these stages on climatic factors (O'Connor et al, 2006), as well as the complexity involved in predicting the overall, often contrasting, effects of climate change on the abundance of infective larvae Morgan and van Dijk, 2012) have been reviewed in detail. Briefly, increases in environmental temperature will increase the proportion of parasite populations being able to develop, as well as development rates of those populations.…”

Do lagomorphs play a relay role in the evolution of the Trichostrongylina nematodes?

“…This may be interpreted as an adaptative phenomenon in order to limit the number of parasites present (massive or repetitive infestations) or to preserve the parasite when conditions are unfavourable in the natural environment, i.e. seasonal influences on infective larvae on pasture (Levine, 1963;Eysker, 1997;O'Connor et al, 2006) or the host immune responses can inhibit the normal development of the parasitic phase of the life cycle (Eysker, 1978, Christensen et al, 1992. In the Heligmosomidae, this arrest of development does not exist since the larvae leave the pseudocyst which disappears at the beginning of the patent period.…”