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Prevalence and Morphological and Molecular Characteristics of Sarcocystis Bertrami in Horses in China

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Prevalence and Morphological and Molecular Characteristics of Sarcocystis Bertrami in Horses in China

Chun-Li Ma et al. Parasite.

Abstract

Three cyst-forming Sarcocystis species have been identified in horsemeat; however, there exists considerable confusion concerning their relationships. Here, 74% (34/46) of the examined tissue samples from horses contained sarcocysts based on examination by light microscopy (LM), and the organism was identified as Sarcocystis bertrami based on cyst structure. The S. bertrami cysts were microscopic (up to 6750 μm in length) and exhibited a striated wall with 2.0-5.1 μm villar protrusions (vps) under LM. Transmission electron microscopy (TEM) observations showed that the vps were tightly packed, similar to "type 11c". Four genetic markers (18S, 28S, ITS1 and the mitochondrial cox1 gene) of S. bertrami were sequenced and analyzed. The 28S and ITS1 sequences are the first records for Sarcocystis in horses. The newly obtained sequences of the 18S and cox1 genes both shared the highest similarities with those of S. bertrami and S. fayeri obtained from horses. Phylogenetic analysis based on the 18S, 28S and cox1 sequences revealed that S. bertrami and S. fayeri formed an independent clade within a group comprising Sarcocystis spp. from ruminants and pigs. Therefore, S. bertrami and S. fayeri are considered to represent the same species of Sarcocystis in horses, and S. fayeri is a junior synonym of Sarcocystis bertrami.

Keywords: Horse; Morphology; Prevalence; Sarcocystis bertrami; Systematics.

Figures

Figure 1
Figure 1
Morphological characteristics of Sarcocystis bertrami sarcocysts isolated from the skeletal muscle of a horse. (A) Sarcocyst (unstained, light microscopy) bound by villar protrusions (vps). Scale bar = 10 μm. (B) Longitudinal section of a sarcocyst (under transmission electron microscopy, TEM). The sarcocyst is surrounded by the host cell (hc), and the sarcocyst wall exhibits numerous vps, which are often bent along the cyst surface. The vps contain bundled microtubules (mt) in the core, which penetrate diagonally into the ground substance (gs). Scale bar = 1 μm. (C) Cross-section of a sarcocyst under TEM. Note the bundle of mt in the gs. Scale bar = 1 μm.
Figure 1
Figure 1
Morphological characteristics of Sarcocystis bertrami sarcocysts isolated from the skeletal muscle of a horse. (A) Sarcocyst (unstained, light microscopy) bound by villar protrusions (vps). Scale bar = 10 μm. (B) Longitudinal section of a sarcocyst (under transmission electron microscopy, TEM). The sarcocyst is surrounded by the host cell (hc), and the sarcocyst wall exhibits numerous vps, which are often bent along the cyst surface. The vps contain bundled microtubules (mt) in the core, which penetrate diagonally into the ground substance (gs). Scale bar = 1 μm. (C) Cross-section of a sarcocyst under TEM. Note the bundle of mt in the gs. Scale bar = 1 μm.
Figure 2
Figure 2
Phylogenetic tree based on 18S rDNA sequences. The tree was built using the maximum parsimony method with the Tree-Bisection-Regrafting algorithm. The analysis involved 36 nucleotide sequences (GenBank accession numbers behind the taxon names) and a total of 1258 positions in the final dataset. The values between the branches represent bootstrap values per 1000 replicates, and values below 50% are not shown. The four new sequences of Sarcocystis bertrami (MH025625MH025628, shown in boldface) formed a clade with S. fayeri from horses, and the clade was within a group comprising Sarcocystis spp. from ruminants and pigs.
Figure 2
Figure 2
Phylogenetic tree based on 18S rDNA sequences. The tree was built using the maximum parsimony method with the Tree-Bisection-Regrafting algorithm. The analysis involved 36 nucleotide sequences (GenBank accession numbers behind the taxon names) and a total of 1258 positions in the final dataset. The values between the branches represent bootstrap values per 1000 replicates, and values below 50% are not shown. The four new sequences of Sarcocystis bertrami (MH025625MH025628, shown in boldface) formed a clade with S. fayeri from horses, and the clade was within a group comprising Sarcocystis spp. from ruminants and pigs.
Figure 3
Figure 3
Phylogenetic tree based on 28S rDNA gene sequences. The tree was built using the maximum parsimony method with the Tree-Bisection-Regrafting algorithm. The analysis involved 21 nucleotide sequences (GenBank accession numbers behind the taxon names) and a total of 3680 positions in the final dataset. The values between the branches represent the bootstrap values per 1000 replicates, and values below 50% are not shown. The two new sequences of Sarcocystis bertrami (MH025629 and MH025630, shown in boldface) formed a clade with S. miescheriana from a pig, and Sarcocystis spp. from ruminants.
Figure 3
Figure 3
Phylogenetic tree based on 28S rDNA gene sequences. The tree was built using the maximum parsimony method with the Tree-Bisection-Regrafting algorithm. The analysis involved 21 nucleotide sequences (GenBank accession numbers behind the taxon names) and a total of 3680 positions in the final dataset. The values between the branches represent the bootstrap values per 1000 replicates, and values below 50% are not shown. The two new sequences of Sarcocystis bertrami (MH025629 and MH025630, shown in boldface) formed a clade with S. miescheriana from a pig, and Sarcocystis spp. from ruminants.
Figure 4
Figure 4
Phylogenetic tree based on mitochondrial cox1 sequences. The tree was built using the maximum parsimony method with the Tree-Bisection-Regrafting algorithm. The analysis involved 40 nucleotide sequences (GenBank accession numbers behind the taxon names) and a total of 936 positions in the final dataset. The values between the branches represent the bootstrap values per 1000 replicates, and values below 50% are not shown. The three new sequences of Sarcocystis bertrami (MH025631MH025633 shown in boldface) formed a clade with S. bertrami and S. fayeri from horses within a group comprising Sarcocystis spp. from pigs and ruminants.
Figure 4
Figure 4
Phylogenetic tree based on mitochondrial cox1 sequences. The tree was built using the maximum parsimony method with the Tree-Bisection-Regrafting algorithm. The analysis involved 40 nucleotide sequences (GenBank accession numbers behind the taxon names) and a total of 936 positions in the final dataset. The values between the branches represent the bootstrap values per 1000 replicates, and values below 50% are not shown. The three new sequences of Sarcocystis bertrami (MH025631MH025633 shown in boldface) formed a clade with S. bertrami and S. fayeri from horses within a group comprising Sarcocystis spp. from pigs and ruminants.

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