Institute of Infection, Veterinary and Ecological Sciences, Department of Infection Biology and Microbiomes, University of Liverpool, Liverpool Science Park IC2, 146 Brownlow Hill, Liverpool, L3 5RF, UK.
Silage Solutions Ltd, Bwlch y Blaen, Pontrhydygroes, Ceredigion, SY25 6DP, UK.
Vet Parasitol. 2020 Sep;285:109218. doi: 10.1016/j.vetpar.2020.109218. Epub 2020 Aug 17.
The parasitic liver fluke, Fasciola hepatica, has a detrimental impact on food security and poses a welfare concern to ruminant livestock. F. hepatica metacercariae, shed from an intermediate mud snail host, encyst on vegetation and present a source of infection to grazing livestock. Feeding grass silage to ruminants is a common practice, however the role it plays in the transmission of F. hepatica remains largely unknown. Our current understanding relies on historical studies that are not representative of current silage production and did not apply molecular methods to detect F. hepatica DNA persistence within silages. This study determined the impact of specific fermentation factors, including grass dry matter (DM) content (20, 30 & 40 %), length of ensiling period and maintaining an anaerobic environment on F. hepatica metacercariae viability. In vitro excystment assays demonstrated that regardless of grass DM content, metacercariae ensiled under anaerobic conditions were not viable from two weeks post-sealing. Metacercariae recovered from ensiled grass of 20 % DM content subjected to aerobic spoilage, remained viable for up to 10 weeks. DNA of F. hepatica remained detectable for up to 10 weeks in both anaerobic and spoiled silages. This study highlights i) the importance of maintaining an anaerobic ensiling environment to eliminate the risk of F. hepatica transmission from silage and ii) an inverse relationship between grass DM content and duration of metacercariae survival within spoiled silages. Improving our understanding of trematode metacercariae survival rates within silages, especially of highly pathogenic species such as F. hepatica, allows farmers to make informed decisions regarding on-farm parasite control.
寄生性肝片吸虫，Fasciola hepatica，对食品安全有不利影响，并对反刍动物的福利构成关切。F. hepatica 的囊蚴从中间泥螺宿主中脱落，在植被上形成囊包，成为放牧牲畜的感染源。给反刍动物喂食青贮饲料是一种常见做法，但它在肝片吸虫传播中的作用在很大程度上仍不清楚。我们目前的理解依赖于历史研究，这些研究不能代表当前的青贮饲料生产情况，也没有应用分子方法来检测青贮饲料中肝片吸虫 DNA 的持续存在。本研究确定了特定发酵因素对肝片吸虫囊蚴活力的影响，包括牧草干物质（DM）含量（20%、30%和 40%）、青贮时间长度和保持厌氧环境。体外脱囊实验表明，无论 DM 含量如何，在厌氧条件下青贮的囊蚴在密封后两周内均无活力。从 20% DM 含量的青贮草中回收的，经历有氧腐败的囊蚴，在长达 10 周内仍具有活力。在厌氧和腐败青贮饲料中，F. hepatica 的 DNA 可检测长达 10 周。本研究强调了 i）保持厌氧青贮环境的重要性，以消除肝片吸虫通过青贮饲料传播的风险；ii）牧草 DM 含量与腐败青贮饲料中囊蚴存活时间之间的反比关系。提高我们对囊蚴在青贮饲料中存活率的理解，特别是对高度致病性的物种如 F. hepatica，使农民能够就农场寄生虫控制做出明智的决策。
