Background and Aim: African swine fever (ASF) is a notifiable viral disease of pigs and wild boars that causes severe economic losses to the swine industry. The pig industry in Vietnam was recently attacked by the ASF virus (ASFV) for the first time in history. However, we lack information regarding the transmissibility of ASF within indoor production systems communities, such as those in Vietnam. Therefore, we aimed to estimate the basic reproduction number (R0) for ASF during the early stages of transmission between farms in indoor production system communities from local and national data in Vietnam. Materials and Methods: The linear regression model approach for the susceptible infectious method was used in this study to estimate the transmission rate and, consequently, the R0 value. Results: The R0 values between-farm of ASF ranged from 1.41 to 10.8 in different scenarios of infectious period duration, from 15 to 30 days at the national and local levels. Conclusion: These results help to understand the scale and speed of ASF infection in Vietnam and to provide a scientific basis to implement control measures to restrict the spread of ASFV in other locations.

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.

Novel waterfowl reoviruses (nWRVs) have been reported in several countries, but their circulation and genetic characteristics in Vietnam remain poorly understood. In this study, we investigated nWRVs in northern Vietnam through molecular detection, virus isolation, experimental infection in ducklings, and molecular analysis of the sigma C-encoding (sC) gene. We also applied immunoinformatic tools to explore the antigenic and structural features of the sC protein. nWRVs were detected in 15.6% of tested samples across ten provinces. Three isolates were successfully recovered, all showing a characteristic cytopathic effect—syncytium formation—in Vero cells. When tested in ducklings (n = 72), the isolates caused disease of varying severity, but all induced characteristic gross and microscopic lesions, particularly ecchymotic hemorrhages and large necrotic foci in the liver and spleen. Phylogenetic analysis based on sC sequences placed the Vietnamese isolates (n = 14) within the nWRV clade, with evidence of two genetically distinct groups. Our immunoinformatic analysis identified four predicted B-cell epitopes located in the head and body domains of the sC protein, with little variation.

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.