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Abstract：
BACKGROUND: The roundworms, Parascaris spp., are important nematode parasites of foals and were historically model organisms in the field of cell biology, leading to many important discoveries. According to karyotype, ascarids in Equus are commonly divided into Parascaris univalens (2n = 2) and Parascaris equorum (2n = 4).
METHODS: Here, we performed morphological identification, karyotyping and sequencing of roundworms from three different hosts (horses, zebras and donkeys). Phylogenetic analysis was performed to study the divergence of these ascarids based on cytochrome c oxidase subunit I (COI) and internal transcribed spacer (ITS) sequences.
RESULTS: Karyotyping, performed on eggs recovered from worms of three different Equus hosts in China, showed two different karyotypes (2n = 2 in P. univalens collected from horses and zebras; 2n = 6 in Parascaris sp. collected from donkeys). There are some differences in the terminal part of the spicula between P. univalens (concave) and Parascaris sp. (rounded). Additionally, it was found that the egg\'s chitinous layer was significantly thicker in Parascaris sp. (> 5 μm) than P. univalens (< 5 μm) (F(2537) = 1967, P < 0.01). Phylogenetic trees showed that the sequences of Parascaris from Equus hosts were divided into two distinct lineages based on sequences of the COI and ITS.
CONCLUSIONS: Comparing the differences in roundworms collected from three different Equus hosts, this study describes a Parascaris species (Parascaris sp.) with six chromosomes in donkeys. It is worth noting that the thickness of the chitinous layer in the Parascaris egg may serve as a diagnostic indicator to distinguish the two roundworms (P. univalens and Parascaris sp.). The Parascaris sp. with six chromosomes in donkeys in the present study may be a species of P. trivalens described in 1934, but the possibility that it is a new Parascaris species cannot be ruled out. Both karyotyping and molecular analysis are necessary to solve the taxonomic problems in Parascaris species.
METHODS: Here, we performed morphological identification, karyotyping and sequencing of roundworms from three different hosts (horses, zebras and donkeys). Phylogenetic analysis was performed to study the divergence of these ascarids based on cytochrome c oxidase subunit I (COI) and internal transcribed spacer (ITS) sequences.
RESULTS: Karyotyping, performed on eggs recovered from worms of three different Equus hosts in China, showed two different karyotypes (2n = 2 in P. univalens collected from horses and zebras; 2n = 6 in Parascaris sp. collected from donkeys). There are some differences in the terminal part of the spicula between P. univalens (concave) and Parascaris sp. (rounded). Additionally, it was found that the egg\'s chitinous layer was significantly thicker in Parascaris sp. (> 5 μm) than P. univalens (< 5 μm) (F(2537) = 1967, P < 0.01). Phylogenetic trees showed that the sequences of Parascaris from Equus hosts were divided into two distinct lineages based on sequences of the COI and ITS.
CONCLUSIONS: Comparing the differences in roundworms collected from three different Equus hosts, this study describes a Parascaris species (Parascaris sp.) with six chromosomes in donkeys. It is worth noting that the thickness of the chitinous layer in the Parascaris egg may serve as a diagnostic indicator to distinguish the two roundworms (P. univalens and Parascaris sp.). The Parascaris sp. with six chromosomes in donkeys in the present study may be a species of P. trivalens described in 1934, but the possibility that it is a new Parascaris species cannot be ruled out. Both karyotyping and molecular analysis are necessary to solve the taxonomic problems in Parascaris species.
摘要：
背景：蛔虫，Parascarisspp.,是小马驹的重要线虫寄生虫，并且是细胞生物学领域的历史模型生物，导致了许多重要的发现。根据核型,马匹中的a虫通常分为Parascisunivalens（2n=2）和Parascisequorum（2n=4）。
方法：这里，我们进行了形态学鉴定，来自三种不同宿主(马，斑马和驴）。基于细胞色素c氧化酶亚基I（COI）和内部转录间隔区（ITS）序列，进行了系统发育分析以研究这些a虫的差异。
结果：核型分析，在从中国三种不同的马宿主的蠕虫中回收的卵上进行，显示出两种不同的核型（从马和斑马中收集的单卵疟原虫中2n=2；在Parascarissp中2n=6。从驴收集)。单价疟原虫（凹形）和Parascissp之间的针状末端部分存在一些差异。（四舍五入）。此外,结果发现，在Parascissp中，卵的几丁质层明显较厚。(>5μm)比单形物(<5μm)(F(2537)=1967,P<0.01)。系统发育树表明，根据COI和ITS的序列，将来自马宿主的Parascar的序列分为两个不同的谱系。
结论：比较从三种不同的马宿主收集的蛔虫的差异，这项研究描述了Parascaris物种（Parascarissp。）驴身上有六个染色体。值得注意的是，parascaris虫卵中几丁质层的厚度可以作为区分两种蛔虫的诊断指标（P。单价和Parascarissp.).Parascarissp.在本研究中，驴中具有六个染色体可能是1934年描述的三谷草的一种，但不能排除它是新的Parascaris物种的可能性。核型分析和分子分析对于解决Parascaris物种的分类问题都是必要的。
方法：这里，我们进行了形态学鉴定，来自三种不同宿主(马，斑马和驴）。基于细胞色素c氧化酶亚基I（COI）和内部转录间隔区（ITS）序列，进行了系统发育分析以研究这些a虫的差异。
结果：核型分析，在从中国三种不同的马宿主的蠕虫中回收的卵上进行，显示出两种不同的核型（从马和斑马中收集的单卵疟原虫中2n=2；在Parascarissp中2n=6。从驴收集)。单价疟原虫（凹形）和Parascissp之间的针状末端部分存在一些差异。（四舍五入）。此外,结果发现，在Parascissp中，卵的几丁质层明显较厚。(>5μm)比单形物(<5μm)(F(2537)=1967,P<0.01)。系统发育树表明，根据COI和ITS的序列，将来自马宿主的Parascar的序列分为两个不同的谱系。
结论：比较从三种不同的马宿主收集的蛔虫的差异，这项研究描述了Parascaris物种（Parascarissp。）驴身上有六个染色体。值得注意的是，parascaris虫卵中几丁质层的厚度可以作为区分两种蛔虫的诊断指标（P。单价和Parascarissp.).Parascarissp.在本研究中，驴中具有六个染色体可能是1934年描述的三谷草的一种，但不能排除它是新的Parascaris物种的可能性。核型分析和分子分析对于解决Parascaris物种的分类问题都是必要的。
