Genetic variability among Schistosoma japonicum isolates from different endemic regions in China revealed by sequences of three mitochondrial DNA genes

Genetic characterization of ticks from southwestern Romania by sequences of mitochondrial cox1 and nad5 genes

In the present study, samples representing three hard tick species and one soft tick species, namely Dermacentor marginatus, Haemaphysalis punctata, Ixodes ricinus and Argas persicus from southwestern Romania, and one hard tick, Haemaphysalis longicornis, from China were characterized genetically by a portion of mitochondrial cytochrome c oxidase subunit 1 gene (pcox1) and a portion of nicotinamide adenine dinucleotide dehydrogenase subunit 5 gene (pnad5). The pcox1 and pnad5 were amplified separately from individual ticks by PCR, sequenced and analyzed. The length of pcox1 and pnad5 sequences of all samples was 732 and 519 bp, respectively. The intra-specific sequence variation in De. marginatus was 0.1-1.0% for pcox1 and 0.2-1.2% for pnad5, whereas in Ha. punctata it was 0.4-1.9% for pcox1 and 0.4-1.0% for pnad5. For the tick species examined in the present study, sequence comparison revealed that the inter-specific sequence differences were higher: 15.9-27.6% for pcox1 and 20.3-42.4% for pnad5. This suggests that the cox1 and nad5 sequences could provide useful genetic markers for the specific identification and genetic characterization of ticks in Romania and elsewhere.

Combined mitochondrial 16S and 12S rDNA sequences: an effective genetic marker for inter-species phylogenetic analysis of zoonotic trematodes

The present study studied the genetic variation among Schistosoma japonicum isolates from different endemic regions in mainland China and examined the phylogenetic relationships of zoonotic trematodes using the combined mitochondrial 16S and 12S ribosomal DNA sequences. The fragments of 16S and 12S rDNA were amplified from 22 S. japonicum isolates, and sequenced, and the relevant sequences of other nine trematode species belonging to six genera in four families were downloaded from GenBank, and their phylogenetic relationships were re-constructed by unweighted pair-group method with arithmetic averages analyses using the combined 16S and 12S rDNA sequences, with Trichinella spiralis as outgroup. The results showed that the partial sequences of mitochondrial 16S and 12S rDNA of S. japonicum were 757 and 797 bp, respectively, and they were quite conserved among the S. japonicum isolates. Phylogenetic analysis revealed that the combined 16S and 12S rDNA sequences were not able to distinguish S. japonicum isolates in mountainous areas from those in lake/marshland areas in mainland China. However, the combined sequences could distinguish different species of zoonotic trematodes. Therefore, the combined mitochondrial 16S and 12S rDNA sequences provide an effective molecular marker for the inter-species phylogenetic analysis and differential identification of zoonotic trematodes.

Analysis of genetic variability within Argulus japonicus from representatives of Africa, Middle East, and Asia revealed by sequences of three mitochondrial DNA genes

This study investigated the genetic variability within fish louse Argulus japonicus (Crustacea: Branchiura) from Africa, Middle East, and Asia by polymerase chain reaction in three mitochondrial DNA (mtDNA) regions, namely, cytochrome c oxidase subunit 1 (cox1) and NADH dehydrogenase subunits 1 and 4 (nad1 and nad4). Six different sequences from a portion of the cox1 gene (pcox1) and a portion of the nad1 and nad4 genes (pnad1 and pnad4) for ten adult specimens from infected fish in China, Egypt, and Syria were amplified separately from individual and the amplicons were subjected to direct sequencing. A + T percentages were 68.8-69% for pcox1, 77.1-77.6% for pnad1, and 60.4-60.9% for pnad4. Among all the collected parasites, A. japonicus sequence variations were 0.0-1.9% for cox1, 0.0-2.3% for nad1, and 0.0-0.8% for nad4. In rivers, sequence variations among all individuals were 0.4-0.8% for cox1, 1.0-2.3% for nad1, and 0.4-0.8% for nad4, while sequence variations among all the collected parasites in fish farms were 0.6-1.9% for cox1, 0.0-1.7% for nad1, and 0.2-0.6% for nad4. The nad1 was the most variable gene among selected markers, while nad4 was a more conserved gene than cox1. All isolates of A. japonicus were sister to Argulus americanus in phylogenetic tree and they grouped together in one sub-clade, while isolates from China and Egypt fish farms were closely clustered together. However, moderate genetic drift and slight mutation could be observed among A. japonicus individuals. These findings demonstrated the convenience and attributes of the three selected mtDNA sequences for population genetic studies of A. japonicus where nad1 is a new and reliable marker to detect the sequence variation among A. japonicus individuals.

Heterogeneity of class I and class II MHC sequences in Schistosoma japonicum from different endemic regions in mainland China

The present study examined sequence variation in class I and class II major histocompatibility complex (MHC) genes among Schistosoma japonicum isolates from different endemic regions in mainland China and assessed the level of horizontal gene transfer and sequence similarity between parasites and their hosts. S. japonicum cercariae were used to infect male adult rabbits to obtain adult S. japonicum samples. A portion of the class I MHC gene (pMHC I) and class II MHC genes (pMHC II) were amplified separately from individual adult trematodes by polymerase chain reaction and sequenced. Among all the examined isolates of S. japonicum, sequence differences between male and female parasites were 0.0-26.6% for pMHC I and 0.0-7.0% for pMHC II. Sequence variations between male and female parasites among different geographical locations from the mountainous areas were 1.1-26.6% for pMHC I and 1.5-3.0% for pMHC II. Sequence variations between samples from Yunnan and those from Sichuan were 2.7-23.5% for pMHC I and 1.1-3.7% for pMHC II. In the lake/marshland areas, sequence variations between male and female parasites among different geographical locations were 0.0-25.0% for pMHC I and 0.0-7.0% for pMHC II. Sequence variations between S. japonicum isolates from mountainous areas, and those from lake/marshland areas were 0.0-26.1% for pMHC I and 0.4-6.1% for pMHC II. BLASTN analysis indicated that all the pMHC II sequences showed high homology to a portion of exon 3 in rabbit MHC class II DP beta gene with more than 89% similarity, and all the pMHC I sequences except isolates in Yunnan (Eryuan) revealed high homology to the portion of exon 2 in rabbit MHC I gene with more than 81% similarity. Phylogenetic analysis showed no specific clustering comprising parasites from single geographical or endemic regions, and the paired parasites were even found in different clusters. These results demonstrated that pMHC I and II of S. japonicum isolates in mainland China existed heterogeneity, but the pMHC I, II, or combined sequences were not suitable markers for examining genetic relationship among different isolates from endemic regions in mainland China.