McElwain Andrew, Warren Micah B, Pereira Felipe B, Ksepka Steven P, Bullard Stephen A
Department of Biological Sciences, College of Liberal Arts and Sciences, State University of New York (SUNY) at Oswego, 30 Centennial Drive, Oswego, NY 13126, USA.
Aquatic Parasitology Laboratory, School of Fisheries Aquaculture and Aquatic Sciences, College of Agriculture, Auburn University, 203 Swingle Hall, Auburn, AL, 36849, USA.
Int J Parasitol Parasites Wildl. 2019 Jun 13;10:41-58. doi: 10.1016/j.ijppaw.2019.05.006. eCollection 2019 Dec.
Little information is available on host-parasite relationships between bivalves and larval nematodes. Herein, we describe nematode larvae (likely stage 2) in the infraorder Ascaridomorpha infecting the foot, intestine, and mantle of a freshwater mussel (Alabama rainbow, [Conrad, 1834]) and detail histopathological changes to infected tissues. A total of 43 live mussels from the South Fork of Terrapin Creek, Alabama, were collected between 2010 and 2014, with 14 sectioned for histopathology and 29 dissected. Of the 14 sectioned mussels, 5 appeared to be uninfected, and 7, 1, and 1 had histozoic infections observed in the foot and intestine, intestine only, and mantle edge and foot, respectively. Twenty-three of 29 (79%) of the mussels dissected were infected by live nematodes, and mean nematode abundance was 8.3 (CL = 5.23-13), with 2 mussels infected with >100 nematodes each. Thus, with a total of 32 of the 43 collected mussels observed with nematodes, overall infection prevalence was 74.4% (CL = 0.594-0.855). The 18S rDNA of this nematode was 99% similar to that of several ascaridids (species of Kathlaniidae Lane, 1914 and Quimperiidae Baylis, 1930) that mature in aquatic/semi-aquatic vertebrates; the recovered 18S phylogenetic tree indicated this nematode from shares a recent common ancestor with (Ascaridomorpha: Quimperiidae; GenBank Accession Number KY476351). Pathological changes to tissue associated with these infections comprised focal tissue damage, but a cellular response was not evident. The Alabama rainbow possibly represents an intermediate or paratenic host. Given these results, the nematode is likely not pathogenic under normal stream conditions; however, high intensity infections in the foot could inhibit pedal extension and retraction; which would have demonstrable health consequences to a freshwater mussel. Based on our review of the bivalve mollusc parasite literature, a collective biodiversity of 61 nematodes reportedly exhibit some degree of symbiosis (from commensal to parasitic) with 21 bivalves (28 nematode spp. from 17 marine bivalve spp.; 33 nematode spp. from 4 freshwater bivalve spp.); only four records exist of putatively parasitic nematodes from Unionida. The present study represents the first description of a nematode species that invades the tissues of a Unionidae species.
关于双壳贝类与线虫幼虫之间的宿主 - 寄生虫关系，目前所知甚少。在此，我们描述了蛔形亚目线虫幼虫（可能为第二期）感染淡水贻贝（阿拉巴马虹彩贻贝，[康拉德，1834年]）的足部、肠道和外套膜的情况，并详细阐述了受感染组织的组织病理学变化。2010年至2014年间，从阿拉巴马州龟溪南支流共采集了43只活贻贝，其中14只用于组织病理学切片，29只进行解剖。在14只进行切片的贻贝中，5只似乎未被感染，7只、1只和1只分别在足部和肠道、仅肠道以及外套膜边缘和足部观察到组织内感染。在解剖的29只贻贝中，有23只（79%）被活线虫感染，线虫平均丰度为8.3（置信区间 = 5.23 - 13），有2只贻贝各自感染了100多条线虫。因此，在采集的43只贻贝中，共有32只观察到有线虫感染，总体感染率为74.4%（置信区间 = 0.594 - 0.855）。这种线虫的18S核糖体DNA与几种在水生/半水生脊椎动物体内成熟的蛔科线虫（1914年莱恩的Kathlaniidae科和1930年贝利斯的Quimperiidae科的物种）的18S核糖体DNA相似度为99%；恢复的18S系统发育树表明，这种来自阿拉巴马虹彩贻贝的线虫与（蛔形亚目：Quimperiidae科；GenBank登录号KY476351）有最近的共同祖先。与这些感染相关的组织病理学变化包括局部组织损伤，但未观察到明显的细胞反应。阿拉巴马虹彩贻贝可能代表中间宿主或转续宿主。基于这些结果，在正常溪流条件下，这种线虫可能不具致病性；然而，足部的高强度感染可能会抑制足的伸展和收缩；这将对淡水贻贝产生明显的健康影响。根据我们对双壳贝类寄生虫文献的综述，据报道共有61种线虫与21种双壳贝类表现出某种程度的共生关系（从共栖到寄生）（17种海洋双壳贝类中有28种线虫；4种淡水双壳贝类中有33种线虫）；关于Unionida目假定寄生线虫的记录仅有4条。本研究首次描述了一种侵入Unionidae科物种组织的线虫物种。
