Animal Science, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia; Department of Animal Science, College of Natural Resources, Royal University of Bhutan, Lobesa, Bhutan.
Animal Science, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia.
Vet Parasitol. 2022 Mar;303:109683. doi: 10.1016/j.vetpar.2022.109683. Epub 2022 Feb 25.
The prevalence of gastrointestinal nematodes (GINs) is dictated by environmental conditions which influence the survival, development, and migration rates of the free-living stages. While the faecal pellet is the most important micro-environment for GINs, limited data on the impact of temperature and faecal water content (FWC) on their survival, development, and migration limits accurate prediction of nematode pasture infectivity. This study investigated the impact of temperature and FWC on the dynamics of the free-living stages of T. vitrinus, T. colubriformis and T. circumcincta by incubating faecal samples from sheep harbouring mono-specific infection of the GINs in temperature-controlled incubators at constant temperatures ranging from 0° to 40°C and nominal target FWCs ranging from 0% to 80% for 8 days. The different life cycle stages (eggs, pre-infective larvae, intra-pellet infective larvae and extra-pellet infective larvae) were enumerated each day using a modified McMaster technique. Multiple linear regression analysis was used to assess the impact of environmental effects on the recovery of each life cycle stage. A one-way ANOVA was used to compare the life cycle stage tallies between species. Survival and development of each life cycle stage were elucidated by fitting the obtained experimental data to an existing mathematical model which described the dynamics of the free-living stages of the GIN lifecycle. Development of eggs to infective larvae were only observed at target temperatures of 20 and 30ºC (and some development at 40 °C for T. colubriformis). This study predicted development of a minimum of 1% of eggs to intra-pellet infective larvae at temperature ranges of 9-39, 10-39 and 10-38ºC with optimum development occurring at 23, 23 and 20ºC for T. vitrinus, T. circumcincta and T. colubriformis, respectively. Development of eggs to intra-pellet infective larvae was observed at nominal FWC targets of 20% and above where increasing FWC up to 60% resulted in increased tallies of intra-pellet infective larvae. The model predicted that development of eggs to intra-pellet infective larvae required a minimum FWC of 13%, 16% and 17% for T. circumcincta, T. colubriformis and T. vitrinus respectively with higher FWC requirements for migration out of the faecal pellets. Development of T. circumcincta eggs to infective larvae was slower than the other species with only 33% of the T. circumcincta eggs predicted to develop to infective larvae at its optimum temperature and FWC as compared to 47% for T. vitrinus and 56% for T. colubriformis.
肠道寄生虫（GINs）的流行受到环境条件的影响，这些条件影响自由生活阶段的生存、发育和迁移率。虽然粪便颗粒是 GINs 的最重要的微观环境，但关于温度和粪便含水量（FWC）对其生存、发育和迁移的影响的数据有限，限制了对寄生虫牧场感染性的准确预测。本研究通过在温度控制培养箱中孵化来自单种感染 GIN 的绵羊的粪便样本，在 0°C 至 40°C 的恒定温度和 0%至 80%的名义目标 FWC 下孵育 8 天，研究了温度和 FWC 对 T. vitrinus、T. colubriformis 和 T. circumcincta 的自由生活阶段动态的影响。使用改良的 McMaster 技术每天对不同的生命周期阶段（卵、前感染性幼虫、内粪便感染性幼虫和外粪便感染性幼虫）进行计数。使用多元线性回归分析评估环境效应对每个生命周期阶段恢复的影响。使用单向方差分析比较不同物种之间的生命周期阶段计数。通过将获得的实验数据拟合到描述 GIN 生命周期自由生活阶段动态的现有数学模型中，阐明每个生命周期阶段的存活和发育。仅在目标温度为 20 和 30°C（和一些在 40°C 下为 T. colubriformis）时观察到卵发育为感染性幼虫。本研究预测在 9-39、10-39 和 10-38°C 的温度范围内，至少有 1%的卵发育为内粪便感染性幼虫，而 T. vitrinus、T. circumcincta 和 T. colubriformis 的最佳发育温度分别为 23、23 和 20°C。在名义 FWC 目标为 20%及以上的情况下，观察到卵发育为内粪便感染性幼虫，而 FWC 增加到 60%会导致内粪便感染性幼虫的计数增加。该模型预测，卵发育为内粪便感染性幼虫需要 T. circumcincta、T. colubriformis 和 T. vitrinus 分别为 13%、16%和 17%的最低 FWC，而从粪便颗粒中迁移出来的 FWC 要求更高。T. circumcincta 卵发育为感染性幼虫的速度比其他物种慢，只有 33%的 T. circumcincta 卵在其最佳温度和 FWC 下预测发育为感染性幼虫，而 T. vitrinus 为 47%，T. colubriformis 为 56%。
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