Opisthorchiasis is a zoonotic parasitic infection caused by small liver fluke species, Opisthorchis viverrini,O. felineus and Clonorchis sinensis, in the family Opisthorchiidae. Vietnam has both species, of which C.sinensis is distributed in the northern and O. viverrini in the central provinces. In addition to the mitochondrialgenomes, the ribosomal DNA sequences (rDNA) of these species are highly needed to obtain for providingmolecular markers in species identification, classification, phylogeny and evolutionary studies. In this study,the near/complete nucleotide sequences of ribosomal transcription units (rTU) from O. viverrini (Vietnamesesample), O. felineus (Russian sample) and C. sinensis (Vietnamese sample) were analyzed. All rTUs for threespecies were determined, which is 7,839 bp for O. viverrini, 6,948 bp for O. felineus and 7,296 bp for C.sinensis containing structures of 18S, ITS1, 5,8S, ITS2 and 28S. The IGS region was not obtained for all threespecies. In all three species, sequence analysis revealed 2 tandem repetitive elements of 47-48 bp/each in ITS1but not in ITS2. The nucleotide sequences of 18S, ITS1, ITS2 and 28S are valuable ribosomal markers that thisstudy provides for diagnosis, identification, taxonomic classification and population genetics. In conclusion,the rTU sequences for the three species of the family Opisthorchiidae have been identified and providesmolecular markers for the use of phylogenetic analysis for species/family classification in the superfamilyOpisthorchioidea and the class Trematoda.

Highly pathogenic avian influenza (HPAI) H5Nx viruses have continually undergone multiple evolutionary dynamics for the generation of various clades, subclades, and genotypes where 2.3.2.2c, and 2.3.4.4 become predominant and co-circulating in Vietnam from 2014 to date. In this study, fifteen H5 sequences in our study and 90 from others from different clades, 0, 1, 1.1, 2.3.2.1a, 2.3.2.1c, 2.3.4, 2.3.4.1, 2.3.4.2, 2.3.4.3 and 2.3.4.4 of H5N1, H5N2, H5N6, were characterized for hemagglutinin (HA) properties, genetic and phylogenetic analyses. Blast searching using the dataset of the full length of two H5N6 viruses revealed one strain, e.g., A/Duck/Vietnam/HT7/2014(H5N6) in May 2014, belonging to the Sichuan 2014-lineage of Group D (Minor). The other strain, A/Chicken/Vietnam/NT3/2017(H5N6)/or CkNT3-2017 in the Spring of 2017, belonged to the Japanese-Korean late 2016-cluster of Group C (Major). This cluster possessed 140NHETS-145del stretch of Leucine/Serine deletion at position 145 in HA1 (S/L145del), distinct from all the 2.3.4.4 H5N6 viruses known to date. There has been no report of the similar CkNT3-2017 of 2.3.4.4 reassortant in Vietnam prior to our study. The migration flyway might be the route for transportation of this novel H5N6 virus from Japan to Vietnam. In addition, the topology revealed another novel subclade of H5N6 (2018–2019) possibly, of the Vietnamese internal reassortments. The “H5Nx” viruses in Vietnam, in fact, have continually undergone multiple evolutionary processes in parallel with those lineages in China and East-Asia. Variations at the key sites in HA and altered genetic characteristics in novel HPAI H5Nx viruses in Vietnam present a caution for the vaccination program and the risk for human infection.

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Nucleotide sequence of ORF5 encoding the antigenic GP5 for 11 strains collected from different geographic localities in the country during 2008-2011 were obtained. These nucleotide sequences were analyzed for molecular properties (nucleotides and amino acids) to determine genotype, phylogenetic and molecular epidemiological characteristics compared with PRRSV circulating in Vietnam and worldwide. Analysis of nucleotides and deduced amino acids showed that there was very high level of nucleotide identity and amino acid homology (98 – 100%) between the Vietnamese and Chinese PRRSV strains. Phylogenetic analysis based on ORF5 nucleotide sequences revealed two large groups, one derived from the North American lineage of genotype 2, including 11 PRRSV isolates in this study and another of the European lineage of genotype 1. In the genotype 2, further subgroups were found among which there were strains of Asia (Vietnam, China, India), strains of the European/North American origin (Austria, US, Denmark) and a 2012-isolated strain from Canada, in a separate subgroup. Regarding to the epidemiological analysis, our isolates collected during 2008-2011, completely followed the endemic peaks occurred in Viet Nam, such as those in 2007-2008 and in 2010-2011. They all were determined as highly virulent strains due to high homology to the highly virulent strains of China occurred in those periods. We have some conclusions to be made that the outbreaks of highly pathogenic PRRSV in Vietnam were epidemiologically associated with the endemics occurred in China and originated from China.

Fasciola hepatica, F. gigantica and “intermediate” forms of Fasciola species, are responsible for fascioliasis in ruminant animals and humans in many countries. There are two forms: “natural/admixed” and “introgressive” hybridization. Vietnam is a "hot spot" country, where the “hybrid” Fasciola forms have been found nationwide. Determination of phylogenetic relationships and genetic distance of these hybrid forms with those in family Fasciolidae and class Trematoda (Phyllum Platyhelminthes) is necessary to confirm their taxonomic classification. In this study, we sequenced the ITS1 and ITS2 for discrimination of two kinds of hybrid Fasciola mentioned above. The deduced amino acid sequences of the entire mitochondrial genes, cytochrome b (cob), nicotinamide dehydrogenase 1 (nad1) and cytochrome oxidase 1 (cox1), from two hybrid Fasciola spp. including Fsp-DL11-VN (from buffalo, admixed hybrid), Fsp-FH1-VN (from human, introgressive hybrid) and “pure” F. gigantica (Fgig-T4V-VN, from cattle) were obtained and combined (cob+nad1+cox1). These sequences were used as markers for phylogenetic analysis together with 28 representative isolates/species of Fasciolidae and Trematoda. Genetic distances between 13 isolates/species in the family Fasciolidae have also been determined to accurately account for their species-relationships. As results, pairwise genetic distance calculation showed that the distance rate was only 0.4% – 0.7% between Fasciola spp. hybrids of Vietnam and China, slightly higher, 1.3 – 2.0% with “pure” F. gigantica, whilist this rate was quite high compared with F. hepatica (5.7% – 5.9%), with Fasciolopsis buski (20.6% – 21.0%), and two other fasciolids, Fasciola jacksoni and Fascioloides magna (11.0% – 12.6%). The phylogenetic tree of 31 strains/species showed 5 distinct groups, corresponding to 5 families, ie., Fasciolidae, Echinostomatidae, Echinochasmidae, Heterophyidae, Opisthorchiidae and an outgroup, Schistosomatidae. Two "hybrid" Fasciola species of Vietnam (Fsp-FH1-VN and Fsp-DL11-VN) grouped with the reference "hybrid" Fsp-GHL-CN strain of China; and “pure” Fgig-T4V-VN with the two “pure” F. gigantica, Fgig-Bali-ID (Indonesia) and Fgig-GX-CN (China). These results confirmed that “hybrid” Fasciola spp. were of the maternally inherited mitochondrial lineage from F. gigantica.