Williams C F, Vacca A R, Lloyd D, Schelkle B, Cable J
School of Biosciences, Cardiff University, Main Building, Museum Avenue, Cardiff CF10 3AT, UK.
Dis Aquat Organ. 2013 Sep 3;105(3):211-23. doi: 10.3354/dao02618.
Spironucleus vortens is a protozoan fish parasite of veterinary and economic importance in the ornamental aquaculture industry. Despite this, key aspects of the life cycle of this organism, including its mode of transmission, have not been fully elucidated. We developed a non-invasive method for quantifying S. vortens in freshwater angelfish, which was then used to investigate parasite transmission and aggregation within host populations. As previously observed for S. meleagridis and S. salmonis, motile S. vortens trophozoites were detected in host faeces using light microscopy. Species-level identification of these flagellates was confirmed using 16S rDNA PCR. Faecal trophozoite counts were significantly correlated with trophozoite counts from the posterior intestine, the primary habitat of the parasite. This novel finding allowed effective prediction of intestinal parasite load from faecal counts. Overall, faecal count data revealed that 20% of hosts harbour 83% of parasites, conforming to the Pareto Principle (80/20 rule) of parasite aggregation with implications for parasite transmission. Trophozoites survived for ≥36 d outside the host within faeces and remained motile at low pH (comparable with that of angelfish stomach). No putative S. vortens cysts were observed in cultures or faecal samples. This calls into question the commonly accepted hypothesis that a protective cyst is required in the life cycle of S. vortens to facilitate transmission to a new host.
旋核涡虫是一种原生动物鱼类寄生虫，在观赏水产养殖业中具有兽医和经济重要性。尽管如此，这种生物生命周期的关键方面，包括其传播方式，尚未完全阐明。我们开发了一种非侵入性方法来量化淡水神仙鱼体内的旋核涡虫，然后用该方法研究寄生虫在宿主种群中的传播和聚集情况。正如之前对火鸡旋核虫和鲑鱼旋核虫的观察，利用光学显微镜在宿主粪便中检测到了活动的旋核涡虫滋养体。使用16S rDNA PCR确认了这些鞭毛虫的物种水平鉴定。粪便滋养体计数与寄生虫主要栖息地后肠中的滋养体计数显著相关。这一新颖的发现使得能够根据粪便计数有效预测肠道寄生虫负荷。总体而言，粪便计数数据显示，20%的宿主携带了83%的寄生虫，符合寄生虫聚集的帕累托原则（80/20规则），这对寄生虫传播具有影响。滋养体在粪便中于宿主体外存活≥36天，并且在低pH值（与神仙鱼胃的pH值相当）下仍保持活动。在培养物或粪便样本中未观察到推定的旋核涡虫囊肿。这对普遍接受的假设提出了质疑，即旋核涡虫的生命周期中需要一个保护性囊肿来促进向新宿主的传播。
