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Background and Aim: Short beak and dwarfism syndrome (SBDS), a highly contagious disease, has been reported in duck farms in Vietnam since 2019. In this study, we evaluated the virulence and characterized the virus obtained from SBDS cases in North Vietnam. Materials and Methods: Polymerase chain reaction was used to detect waterfowl parvovirus in ducks, and the virus from positive samples was inoculated into 10-day-old duck-embryonated eggs to reproduce the disease in young ducklings to determine the virulence and subjected to phylogenetic analysis of non-structural (NS) and VP1 gene sequences. Results and Discussion: Goose parvovirus (GPV) was isolated from ducks associated with SDBS in Vietnam. The virus Han-GPV2001 is highly virulent when inoculated into 10-day-old duck embryos and 3-day-old ducklings. The mortality rate of duck embryos was 94.35% within 6 days of virus inoculation. Inoculating 3-day-old ducks with the virus stock with 104.03 EID50 through intramuscular and neck intravenous administration resulted in 80% and 66.67% of clinical signs of SDBS, respectively, were shown. Phylogenetic analysis based on the partial NS and VP1 gene sequences revealed that the viral isolate obtained in this study belonged to novel GPV (NGPV) and was closely related to previous Vietnamese and Chinese strains. Conclusion: A GPV strain, Han-GPV2001, has been successfully isolated and has virulence in duck-embryonated eggs as well as caused clinical signs of SBDS in ducks. Phylogenetic analyses of partial genes encoding NS and capsid proteins indicated that the obtained GPV isolate belongs to the NGPV group.

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A total of 97 out of 245 carcass, sewage effluent, and table surface samples in meat shops at the retail markets in North Vietnam showed Salmonella positive. Eleven Salmonella serovars, including Infantis, Anatum, Rissen, Reading, London, Typhimurium, Enteritidis, Agona, Newport, Emek, and Derby, were identified. The Salmonella isolates were tested for antimicrobial susceptibility and further investigated for antimicrobial resistance genes. Resistance to kanamycin, gentamicin, neomycin, nalidixic acid, chloramphenicol, trimethoprim, streptomycin, tetracycline, ampicillin, and sulphonamides was found in 28.9-56.7%. The isolates were neither resistant to ceftazidime nor norfloxacin. Sixty-four (66.0%) out of 97 isolates were resistant to at least one of 14 antimicrobials, and 55 (85.9%) out of the 64 isolates showed multidrug resistance. Thirteen resistance genes (bla(TEM), bla(OXA-1), aadA1, sul1, tetA, tetB, tetG, cmlA1, floR, dfrA1, dfrA12, aac(3)-IV, and aphA1-1AB) were detected in the resistant isolates. This study indicates that Salmonella isolated from meat shops were resistant to multiple antimicrobials, and the resistance genes were widespread among the serovars isolated.

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A total of 118 Salmonella isolates were detected from 283 retail meat samples (135 pork and 148 chicken meat) purchased at retail markets in Northern Vietnam. Thirteen serovars, including Infantis, Anatum, Rissen, Reading, Emek, Typhimurium, Blockley, London, Newport, Derby, Weltevreden, Albany, and Hadar, were determined. Resistance to tetracycline (54.2%), sulfonamides (52.5%), streptomycin (41.5%), trimethoprim (36.4%), chloramphenicol (35.6%), and ampicillin (33.1%) was commonly seen in the Salmonella isolates. Fourteen [bla(TEM), bla(OXA-1), bla(PSE-1), aadA1, sul1, tetA, tetB, tetG, cmlA1, floR, dfrA1, dfrA12, aac(3)-IV, and aphA1-1AB ] of 17 resistance genes were detected from the isolates demonstrating resistance. Genes for plasmid-mediated quinolone resistance, such as qnrA, qnrB, qnrS, qepA, and acc(6')-1b-cr, were not detected in 23 quinoloneresistant isolates. The substitution TCC to TTC at codon 83 of gyrA was found in the 18 quinolone-resistant isolates. The data revealed that resistant Salmonella strains were widely distributed in Northern Vietnam via the food chain and that they might contain multiple genes specifying identical resistance phenotypes. Thus, further studies are necessary to clarify the mechanisms of antibiotic resistance in Salmonella strains and their spread in the livestock market.

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Approximately 39.9% (63/158) of beef samples collected from retail markets in Hanoi from January to June 2009 were Salmonella-positive. Nine Salmonella serovars, Anatum (28.6%), Rissen (25.4%), Weltevreden (12.7%), Typhimurium (7.9%), Derby (7.9%), Lexington (7.9%), Dublin (4.6%), Newport (3.2%) and London (1.8%), were identified. Thirty-seven (58.7%) of the 63 Salmonella isolates were resistant to at least one antimicrobial tested, of which 29 (46%) isolates showed multidrug resistance (MDR). The isolates were commonly resistant to tetracycline (46.0%), sulphonamide (39.7%), ampicilline (31.7%), streptomycin (30.2%), trimethoprim (28.6%), kanamycin (28.6%) and chloramphenicol (22.2%). Fourteen (bla(TEMV), bla(OXA-1), aadA1, aadA2, sul1, tetA, tetB, tetG, cmlA1, floR, dfrA1, dfrA12, aac (3)-IV and aphA1-1AB) out of 22 antimicrobial resistance genes were detected by PCR from the resistant isolates. The catA1, Kn, blaPSE-1 genes and plasmid-mediated quinolones resistance (PMQR) genes such as qnrA, qnrB, qnrS, qepA and acc (6')-ib-cr were not detected. Mutations in the gyrA gene leading to the amino acid changes Ser83Phe and/or Asp87Asn were found in 6 out of the 11 quinolone-resistant isolates. The data revealed that multidrug resistant Salmonella strains were widely distributed in north Vietnam via the food chain and might contain multiple genes specifying identical resistant phenotypes. Thus, continuous studies are necessary to clarify the mechanisms of MDR in Salmonella and its spread in the livestock market.

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The spread of antibiotic resistance via meat poses a serious public health concerns. During 2007-2009, a total of 586 retail meat samples (318 pork and 268 chicken meats) were collected from three provinces (Bac Ninh, Ha Noi and Ha Tay) of North Vietnam to determine the prevalence of Salmonella. Isolates were characterized by serotyping and antibiotic susceptibility testing. Approximately 39.6% (n=126) of pork and 42.9% (n=115) of chicken samples were Salmonella-positive, and 14 Salmonella serovars were identified. Anatum (15.8%) was the most common serovar, followed by Infantis (13.3%), Emek (10.4%), Derby and Rissen (9.5%), Typhimurium (9.1%), Reading (7.5%) and London (6.2%). The isolation frequency of serovars Enteritidis, Albany, Hadar, Weltevreden, Newport and Blockey ranged from 1.2%-5.8%. Resistance to at least one antibiotic agent was detected in 78.4% of isolates (n=189) and the most frequent resistance were to tetracycline (58.5%), sulphonamides (58.1%), streptomycin (47.3%), ampicillin (39.8%), chloramphenicol (37.3%), trimethoprim (34.0%) and nalidixic acid (27.8%). No Salmonella isolates were resistant to ceftazidime. Chicken isolates had higher resistance to antibiotic agents than pork isolates (P<0.05). It showed that 159 Salmonella isolates belong to the 14 serovars were multidrug resistant (MDR) and 50 MDR patterns were found. This study indicated that Salmonella serovars isolated from retail meat samples were resistant to multiple antibiotics and this resistance was widespread among different serovars. The widespread resistance may have arisen from misuse or overuse of antibiotics during animal husbandry in North Vietnam.

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