Duck Tembusu virus in North Vietnam: epidemiological and genetic analysis reveals novel virus strains.

Tembusu virus (TMUV) is an important infectious disease, causing economic losses in duck production. Since the first report of TMUV infection in Vietnam in 2020, the disease has persisted and affected poultry production in the country. This study conducted epidemiological and genetic characterization of the viral strains circulating in north Vietnam based on 130 pooled tissue samples collected in six provinces/cities during 2021. The TMUV genome was examined using conventional PCR. The results indicated that 21 (16.15%) samples and 9 (23.68%) farms were positive for the viral genome. The positive rate was 59.26% for ducks at ages 2-4 weeks, which was significantly higher than for ducks at ages >4 weeks and < 2 weeks. Genetic analysis of the partial envelope gene (891 bp) sequences indicated that the five Vietnamese TMUVs shared 99.55-100% nucleotide identity, while the rates were in the range 99.59-100% based on the pre-membrane gene sequences (498 bp). The five Vietnamese TMUV strains obtained formed a novel single subcluster. These strains were closely related to Chinese strains and differed from the vaccine strain, suggesting that Vietnamese TMUV strains were field viruses. It needs to be further studied on vaccine development to prevent effects of TMUV infection on poultry production across Vietnam.

Porcine Sapovirus in Northern Vietnam: Genetic Detection and Characterization Reveals Co-Circulation of Multiple Genotypes.

Porcine sapovirus (PoSaV) has been reported in many countries over the world, which may cause gastroenteritis symptoms in pigs with all ages. There has been no report on PoSaV infection in Vietnam up to now. In this study, a total of 102 samples were collected from piglets, fattening pigs, and sows with diarrhea in several cities and provinces in northern Vietnam. The PoSaV genome was examined using polymerase chain reaction (PCR). Sequencing of the partial RNA-dependent RNA polymerase (RdRp) gene sequences (324 bp) was performed. Of the 102 tested samples, 10 (9.8%) and 7/20 (35%) were detected as positive for the PoSaV RdRp gene using the PCR method at the individual and farm levels, respectively. Genetic analysis of the partial RdRp gene region of about 324 bp indicated that the nucleotide identity of the current 10 Vietnamese viral strains ranged from 61.39% to 100%. Among the 10 strains obtained, 8 belonged to genotype III and the remaining 2 strains were clustered in genotype VIII. The Vietnamese genotype III viruses formed two sub-clusters. The Vietnamese PoSaV strains were closely related to PoSaVs reported in South Korea, Venezuela, and the Netherlands. This research was the first to describe PoSaV infection in northern Vietnam during 2022-2023.

Epidemiological Analysis and Genetic Characterization of Parvovirus in Ducks in Northern Vietnam Reveal Evidence of Recombination.

In total, 130 tissue-pooled samples collected from ducks in some provinces/cities in north Vietnam were examined for waterfowl parvovirus genome identification. Twenty-six (20%) samples were positive for the parvovirus infection, based on polymerase chain reaction analysis. Of the 38 farms tested, 14 (36.84%) were positive for the waterfowl parvovirus genome. The rate of the parvovirus genome detection in ducks aged 2−4 weeks (37.04%) was significantly (p < 0.05) higher than that at ages <2 weeks (9.09%) and >4 weeks (16.30%). The positive rate on medium-scale farms (9.36%) was significantly (p < 0.05) lower than for small-scale (31.03%) and large-scale (29.73%) farms. The lengths of the four Vietnamese waterfowl parvovirus genomes identified were 4750 nucleotides. Among the four Vietnamese parvovirus genomes, nucleotide identities were from 99.29% to 99.87%. Phylogenetic analysis of the near-complete genomes indicated that the waterfowl circulating in northern Vietnam belonged to the novel goose parvovirus (NGPV) group. The Vietnamese NGPV group was closely related to the Chinese group. Recombination analysis suggested that the Vietnam/VNUA-26/2021 strain was generated by a recombination event. One positive selection site of the capsid protein was detected.

Duck circovirus in northern Vietnam: genetic characterization and epidemiological analysis.

In the present study, tissue samples collected from 130 ducks from clinically suspected commercial flocks and diseased birds in six provinces of northern Vietnam were tested for duck circovirus (DuCV) infection. The DuCV genome was detected in 56 out of 130 (43.08%) duck samples by PCR. Of 38 tested farms, 26 (68.42%) were positive for the DuCV genome. The rate of the DuCV genome detection in ducks at 3-4 weeks of age (54.17%) was significantly higher (p < 0.05) than that at <3 (32.43%) and >7 (33.33%) weeks of age and insignificantly higher than that at 5-7 weeks of age (43.33%) (p = 0.11). The genomes of six Vietnamese DuCV isolates were determined. They ranged in length from 1,988 to 1,995 nucleotides, and their nucleotide sequences were 83.24% to 99.69% identical to each other. Phylogenetic analysis based on the complete genome sequences indicated that the DuCV strains circulating in northern Vietnam can be divided into two main genotypes (I and II) and several subgenotypes. The Vietnamese DuCV isolates were closely related to Chinese, Taiwanese, and Korean strains. One positively selected site was detected in the capsid protein.

Genetic characterization of chicken anemia viruses newly isolated from diseased chicks in Japan in 2020.

In this study, a total of nine chicken samples obtained from two broiler flocks in Oita and Tottori prefectures in 2020 were examined for Chicken anemia virus (CAV) infection. The samples were collected from clinically suspected flocks and diseased chickens. The CAV genome was detected in all nine samples tested by real-time PCR. Phylogenetic analyses and sequence comparisons of the full-length VP1 gene sequences indicated that all the Japanese CAV strains obtained in this study formed a similar cluster of genotype III and shared high nucleotide (99.62-100%) identity. The current Japanese CAV strains were closely related to Chinese CAV strains but not related to vaccine strains. One positive selection site of VP1 was detected among the Japanese CAV strains.

Establishment of an In Vitro Model of Persistent Chicken Anemia Virus Infection.

Persistent infection of chicken anemia virus (CAV) in chickens has been suspected to result in immunosuppression and exogenous virus contamination within vaccine production. However, no direct evidence for persistent CAV infection has thus far been obtained. In this study, we aimed to establish an in vitro model of persistent CAV infection. CAV-infected MDCC-MSB1 (MSB1) cells, a Marek's disease virus-transformed continuous cell line, were cultured in the presence of both CAV and CAV neutralizing antibody (NA). Cell viability, expression of viral antigens, viral DNA, and recovery of CAV were examined by acridine orange/propidium iodide staining, immunofluorescence measurement, real-time PCR, and viral isolation, respectively. The results indicated that CAV was maintained and possibly replicated in CAV-infected cells cultured in the presence of NA, without affecting host cell viability. It was also shown that persistently infectious CAV induced cell death again after removing NA. The persistent infection of CAV in MSB1 cells was not related to viral gene mutation. In summary, we have herein established a novel model of persistent CAV infection in MSB1 cells cultured in the presence of NA.

Molecular characterization of full genome sequences of Newcastle disease viruses circulating among vaccinated chickens in Egypt during 2011-2013.

Although intensive vaccination programs have been implemented, Newcastle disease (ND) outbreaks, accompanied by severe economic losses, are still reported in Egypt. The genetic characterization of ND virus (NDV) strains isolated from ND-vaccinated chicken flocks provides essential information for improving ND control strategies. Therefore, here, 38 NDV strains were isolated and identified from outbreaks among vaccinated flocks of broiler chickens located in the provinces of Qena, Luxor, and Aswan of Upper Egypt during 2011-2013. The investigated broiler chicken flocks (aged 28 to 40 days) had high mortality rates of up to 80%. All NDV isolates were genetically analyzed using next-generation DNA sequencing. From these isolates, 10 representative NDV strains were selected for further genetic analyses. Phylogenetic analysis of full-length coding genes revealed that the Egyptian NDV isolates belonged to a single sub-genotype, VII.1.1. These isolates were phylogenetically distant from the vaccine strains, including La Sota or Clone 30 (genotype II), which have been commonly used to vaccinate chicken flocks. Amino acid substitution K78R was observed in the neutralizing epitopes of the F proteins; whereas several mutations were found in the neutralizing epitopes of the hemagglutinin-neuraminidase proteins, notably, E347K. Overall, our results suggested that the occurrence of neutralizing epitope variants may be one of potential reasons for ND outbreaks. Further studies are needed to determine the protective effect of current vaccines against circulating virulent NDV strains.

Chicken anemia virus in northern Vietnam: molecular characterization reveals multiple genotypes and evidence of recombination.

Chicken anemia virus (CAV) has a ubiquitous and worldwide distribution in the chicken production industry. Our group previously reported a high seroprevalence of CAV in chickens from northern Vietnam. In the present study, tissue samples collected from a total of 330 broiler and breeder commercial chickens in eleven provinces of northern Vietnam were tested for CAV infection. All samples were collected from clinically suspected flocks and diseased birds. The CAV genome was detected in 157 out of 330 (47.58%) chicken samples by real-time PCR. The rate of CAV genome detection in young chickens at 2-3 weeks of age (61.43%), which had not been previously reported in Vietnam, was significantly higher than that in older chickens at 4-11 (44.83%) and 12-28 (35.71%) weeks of age. For nine representative CAV strains from broiler chickens, analysis of the entire protein-coding region of the viral genome was conducted. Phylogenetic analysis of the VP1 gene indicated that the CAVs circulating in northern Vietnam were divided into three distinct genotypes: II, III, and V. Only one of the nine Vietnamese CAV strains clustered with a vaccine strain (Del-Ros), whereas the other eight strains did not cluster with any vaccine strains. Among the three genotypes, genotype III was most widely found in northern Vietnam and this included three sub-genotypes (IIIa, IIIb, and IIIc). The Vietnamese CAV strains were closely related to the Chinese, Taiwanese, and USA strains. One strain was defined to be of genotype V, which is a newly reported CAV genotype. Moreover, recombination analysis suggests that this novel genotype V was generated by recombination between genotype II and sub-genotype IIIc.