Prevalence, biosecurity factor, and antimicrobial susceptibility analysis of Salmonella species isolated from commercial duck farms in Korea.

Duck meat consumption in South Korea has increased in recent years, but no standard about duck farm-specific biosecurity and hygiene guidelines have yet been established. We here investigated Salmonella contamination levels in duck farms to evaluate biosecurity and hygiene practices. We collected 1,116 environmental samples from 31 duck farms in Jeonnam Province, South Korea. The Salmonella-positive farm rate dramatically increased, from 22.6 to 71.0%, on introduction of ducklings. As the ducklings aged 4-6 wk, the positive rate slightly decreased to 64.5%. The Salmonella detection rate on each sampled surface, such as the feed pan (34.4%), wall (33.9%), litter (32.3%), and nipples (24.2%), was highest at 3 wk of age. The most frequently detected Salmonella serovars were Salmonella London (22.2%), Salmonella Albany (21.6%), Salmonella Bareilly (17.0%), and Salmonella Indiana (16.5%). Implementation of cleaning and disinfection procedures, rodent control, and metal house walls significantly lowered the prevalence of Salmonella (P < 0.001, P < 0.01, and P < 0.05, respectively). A high proportion of Salmonella isolates exhibited antimicrobial resistance: 100 and 62.9% exhibited resistance to erythromycin and nalidixic acid, respectively. Furthermore, a majority of S. Albany and all Salmonella Enteritidis isolates were multidrug resistant. These results indicate the level of Salmonella contamination in duck farm environments in Korea is high. Good biosecurity and hygiene practices are the most effective measures for controlling Salmonella contamination.

The difference of detection rate of avian influenza virus in the wild bird surveillance using various methods.

Korea is located within the East Asian-Australian flyway of wild migratory birds during the fall and winter seasons. Consequently, the likelihood of introduction of numerous subtypes and pathotypes of the Avian influenza (AI) virus to Korea has been thought to be very high. In the current study, we surveyed wild bird feces for the presence of AI virus that had been introduced to Korea between September 2017 and February 2018. To identify and characterize the AI virus, we employed commonly used methods, namely, virus isolation (VI) via egg inoculation, real-time reverse transcription-polymerase chain reaction (rRT-PCR), conventional RT-PCR (cRT-PCR) and a newly developed next generation sequencing (NGS) approach. In this study, 124 out of 11,145 fresh samples of wild migratory birds tested were rRT-PCR positive; only 52.0% of VI positive samples were determined as positive by rRT-PCR from fecal supernatant. Fifty AI virus specimens were isolated from fresh fecal samples and typed. The cRT-PCR subtyping results mostly coincided with the NGS results, although NGS detected the presence of 11 HA genes and four NA genes that were not detected by cRT-PCR. NGS analysis confirmed that 12% of the identified viruses were mixed-subtypes which were not detected by cRT-PCR. Prevention of the occurrence of AI virus requires a workflow for rapid and accurate virus detection and verification. However, conventional methods of detection have some limitations. Therefore, different methods should be combined for optimal surveillance, and further studies are needed in aspect of the introduction and application of new methods such as NGS.