Background and Aim: Newcastle disease (ND) is a major viral disease of poultry worldwide. However, data on the molecular characterization of Newcastle disease virus (NDV) in Vietnam are limited. This study aimed to identify the molecular characteristics of NDV strains from the vaccinated chickens farmed in Northern Vietnam. Materials and Methods: We used reverse-transcription polymerase chain reaction (PCR), sequencing and phylogenetic analysis to characterize NDV strains from vaccinated chicken farms in Northern Vietnam. Results: Seven out of 72 (9.7%) chicken tissue samples collected from seven chicken farms in the four cities/provinces in northern Vietnam were positive for the NDV genome by PCR method. The complete sequences of the fusion (F) and hemagglutinin-neuraminidase (HN) genes of NDVs isolated in the North of Vietnam from 2021 to 2022 were further evaluated. The results indicated that all seven Vietnamese isolates obtained were reported as virulent NDV strains with the amino acid (AA) sequence of the F0 protein proteolytic cleavage site motif (112RRRKRF117). Phylogenetic analysis revealed that they were grouped with other NDV class II from subgenotype VII.2, including the two previous Vietnamese NDV (2015), the Chinese (2017), and Southern African (2013) NDV strains. In addition, some AA substitutions were observed in the neutralizing epitopes of the F and HN proteins of the current Vietnamese NDV strains. Conclusion: The present findings provide useful information for future studies of the evolution of NDVs and improve strategies for ND-controlling programs in Vietnam. Keywords: genetic characterization, Newcastle disease virus, Vietnam, genotype VII.2, virulent strain.

To date, many fluorescence- and gel-based multiplex polymerase chain reaction (PCR) assays have been developed for the simultaneous detection of multiple infectious agents of respiratory disease in poultry. However, PCR assays are not available for other important emerging respiratory bacteria, such as Ornithobacterium rhinotracheale (ORT). We aimed to fill this gap by establishing a new duplex PCR method for the simultaneous detection of infectious laryngotracheitis virus (ILTV) and ORT. Multiplex primer design software was used to select the compatible multiplex primer pairs. It was determined that an annealing temperature of 65 °C and an initial concentration of 2.5 pmol/µL for each primer set were the most suitable conditions for multiplex PCR. The assay was confirmed to be specific, as it only detected the target pathogens, even in the presence of six non-target agents. The limit of detection was up to 10³ copies/µL of template DNA for both ILTV and ORT. In the screening of 304 field samples, 23, 88, and 44 were positive for both ILTV and ORT, solely for ILTV, and solely ORT, respectively.

Background and Aim: Many studies have reported on the phenomenon of co-infections involving two or more pathogens (bacteria or viruses) over the past few years. However, very few studies on this issue were conducted in Vietnam. Therefore, this study aimed to determine the circulation of single and multiple porcine parvovirus (PPV) (e.g., PPV1, PPV2, PPV3, and PPV4), porcine bocavirus (PBoV), and torque teno virus (TTV) (TTV1 and TTV2) infections in Vietnamese pigs. Materials and Methods: A total of 174 porcine circovirus 2-positive samples from pigs (n = 86 for 2017 and n = 88 for 2021), including from the sera and internal organs, across 11 provinces were examined by polymerase chain reaction. Results: This study demonstrated the wide distribution of DNA viruses among pig farms in Vietnam in 2021, with the detection rate for PPV ranging from 3.4% to 27.3% among PPV1-PPV4. Moreover, the detection rates of TTV genotypes were confirmed to be 14.8% (TTV1) and 63.6% (TTV2), respectively, and the positive rate of PBoV was 65.9%. The most frequent combinations were double and triple infections. Double infection was found in 16/86 (18.6%) in 2017 and 26/88 (29.5%) in 2021, while triple infection was found at 19/86 (22.1%) in 2017 and 26/88 (29.5%) in 2021. The incidence of simultaneous detection of more than three viruses was low. Conclusion: These results provide at least partial information about the occurrence of three viruses, including PPV (including PPV1 to 4), PBoV, and TTV (TTV1 and TTV2), in pigs. Determination of particular viruses in pigs will help to prevent the porcine respiratory disease complex caused by DNA viruses in Vietnamese pigs in the future.

The metabolic capacity of swine caecum-derived Lactobacillus spp. to biotransform mycotoxins presents promising potential as a host-probiotic strategy to improve pig health and support host-targeted probiotic research. In the present study, Lactobacillus spp. isolated from the pig caecum were examined for their ability to detoxify fumonisin B1 (FB1) in vitro. Three experimental groups were established (i) Control 1 (C1: buffer + caecal chyme), (ii) Control 2 (C2: buffer + FB1), (iii) Experimental group (E: buffer + caecal chyme + FB1), each with 12 replicates per group (4 replicates per time point 0, 24, and 48 h). Quantitative polymerase chain reaction (qPCR) was used to determine bacterial abundance, while fumonisin B1 (FB1) and its hydrolyzed product (HFB1, Hydrolyzed Fumonisin B1), were quantified using liquid chromatography–mass spectrometry (LC-MS). Group E showed a significant increase in Lactobacillus spp. abundance (p < 0.001), indicating a selective microbial response to FB1 exposure. In contrast, total bacterial counts did not differ significantly between C1 and E (p = 0.35), suggesting that the proliferation of Lactobacillus was the main microbiological outcome supporting the host–probiotic hypothesis. Principal component analysis (PCA) revealed distinct microbial clustering, explaining 97.3% of the variance. Compared to C2, FB1 levels in group E were significantly reduced at 24 and 48 h, while HFB1 conversion rates increased from 47.1% to 56.5%. The study identified Lactobacillus pontis, Lactobacillus amylovorus, and Lactobacillus ultunensis as promising host-associated probiotics, with potential application as feed additives to mitigate mycotoxin effects in pigs. These findings warrant further in vivo validation.

Background and Aim: Avian pathogenic Escherichia coli (APEC), a major cause of colibacillosis in poultry, possesses diverse virulence-associated genes (VAGs) that contribute to extraintestinal pathogenicity. However, comprehensive information on VAG combinations and co-occurrence patterns among APEC isolates in Vietnam remains limited. This study aimed to characterize VAG prevalence, combination profiles, and co-occurrence patterns in APEC and non-pathogenic E. coli (NPEC) isolates from chickens in northern Vietnam. Materials and Methods: From August 2023 to August 2025, 515 spleen samples were collected from healthy and non-healthy chickens on 35 commercial poultry farms in Hanoi, Hai Phong, Phu Tho, Bac Ninh, and Thai Nguyen. A total of 200 E. coli isolates were recovered and screened by multiplex polymerase chain reaction for 19 VAGs: fimC, eaeA, papC, tsh, sfa_foc, iucD, iutA, irp2, fyuA, iucA, iroN, vat, hlyA, hlyF, astA, ompT, iss, cva/cvi, and colV. Isolates carrying ≥5 of nine selected APEC-associated VAGs were classified as APEC; the remainder were classified as NPEC. We compared gene prevalence, combination profiles, and pairwise co-occurrence using appropriate statistical tests and Jaccard similarity analysis. Results: Among 200 isolates, 121 (60.5%) were classified as APEC and 79 (39.5%) as NPEC. APEC isolates most frequently carried hlyF (100%), fimC and iutA (96.7% each), ompT and iucD (95.9% each), iss (90.1%), irp2 (79.3%), and iroN (65.3%). APEC isolates contained up to 19 VAGs, whereas NPEC isolates contained up to 14. Twenty-three distinct VAG combination profiles were identified among APEC isolates, and 103/121 (85.1%) harbored >8 VAGs. In contrast, NPEC isolates displayed 13 less complex profiles containing 3–6 VAGs. Most VAGs were significantly more prevalent in APEC than in NPEC isolates, while papC, fyuA, and eaeA occurred exclusively in APEC. Co-occurrence analyses demonstrated greater complexity and stronger VAG associations among APEC isolates. Conclusion: APEC isolates from northern Vietnam exhibited extensive VAG diversity and complex co-occurrence patterns distinct from those of NPEC isolates. These findings provide a molecular basis for improved APEC characterization, epidemiological surveillance, and targeted control of poultry colibacillosis. Keywords: avian pathogenic Escherichia coli, chickens, colibacillosis, gene co-occurrence, northern Vietnam, poultry, virulence-associated genes, virulence profiles.