The plasmid-borne fosfomycin resistance gene fosA3 has been identified in Escherichia coli ( E. coli) from various animals but has rarely been reported in ducks. In this study, we investigated the fosA3 prevalence and molecular characteristics of fosA3-harboring E. coli strains from ducks in Shandong province of China. In 416 E. coli isolates, 91 (21.88%) were identified as fosA3-bearing strains, and the fosfomycin-resistant phenotype of 88 of the 91 fosA3-harboring strains was successfully transferred to the recipient strains. Seven different genetic structures surrounding the fosA3 gene were detected and 2 new contexts were discovered among the fosA3-carrying E. coli. Twenty fosA3-harboring isolates and their trans-conjugants were randomly selected for pulsed-field gel electrophoresis (PFGE) typing and S1-nuclease PFGE, respectively. The PFGE patterns revealed that the 20 randomly selected fosA3-bearing isolates were not a result of clonal dissemination. S1-PFGE showed that 15 of the 20 randomly selected trans-conjugants carried a single plasmid, and these 15 plasmids that harbored fosA3 (55–190 kb) were distributed into the following replicon types: IncF (n = 11), IncI1 (n = 1), IncN (n = 1), untypable (n = 1), and W-FIC (n = 1). Additionally, as vectors for fosA3 in E. coli, F-:A1:B6, N/ST1, IncI1/ST2, W-FIC, and one untypable plasmid had never been reported before. These observations highlighted the importance of ducks as a reservoir for multidrug-resistant fosA3-carrying E. coli.

With the continuous development of duck farming and the increasing breeding density, the incidence of duck hepatitis A virus type 1 (DHAV-1) has been on the rise, seriously endangering the development of duck farming. To reduce the use of antibiotics in duck breeding, susceptibility risks and mortality, and avoid virulence recovery and immune failure risk, this study aims to develop a new type of mucosal immune probiotics and make full use of molecular biology techniques, on the level of genetic engineering, to modify Lactococcus lactis (L. lactis). In this study, a secretory recombinant L. lactis named MG1363-VP1 with an enhanced Green Fluorescent Protein (eGFP) and translation enhancer T7g10L was constructed, which could express the VP1-eGFP fusion protein of DHAV-1. The animal experiment in ducklings was performed to detect the immune response and protection effect of oral microecologics by recombinant L. lactis. The results showed that oral L. lactis MG1363-VP1 significantly induced the body’s humoral immune system and mucosal immune system to produce specific anti-VP1 IgG antibodies and mucosal secretory immunoglobulin A (sIgA) for DHAV-1 in ducklings, and cytokines including interleukin-2 (IL-2), interleukin-4 (IL-4), interleukin-10 (IL-10), and interferon gamma (IFN-γ). The mortality rate was monitored simultaneously by the natural infestation in the process of production and breeding; notably, the ducklings vaccinated with L. lactis MG1363-VP1 were effectively protected against the nature infection of DHAV-1. The recombinant L. lactis MG1363-VP1 constructed in this study provides a new means of preventing and controlling DHAV-1 infection in the future.

Since 2023, an infectious upper respiratory tract disease has been persisted in outbreaks among in a flock of Cherry Valley ducks in Shandong Province, China. This outbreak was traced to avian metapneumovirus subtype C (aMPV-C), a significant pathogen associated with egg-drop and acute respiratory diseases in poultry. It is noteworthy that prior to this, aMPV-C infection had not been previously documented in Cherry Valley ducks within China. In this study, we successfully isolated and characterized the aMPV-C LY0913 strain from the affected Cherry Valley duck flock. Sequence analysis showed that the fusion (F) protein of LY0913 exhibited a 97.8-98.7 % amino acid similarity with seven other aMPV-C strains, displaying the closest relationship to the strains isolated from Muscovy ducks in southern China in 2010. Furthermore, five concurrent amino acid mutations were identified in the F protein, providing valuable insights into the outbreak of aMPV-C in Cherry Valley ducks. The LY0913 strain demonstrated typical cytopathic effects on Vero cells and caused mortality in Cherry Valley duck embryos. In vivo infection of Cherry Valley ducklings with LY0913 reproduced the typical clinical signs and pathological lesions observed in the original infected cases. This study is the first to identify aMPV-C as a causative agent of respiratory disease in Cherry Valley ducks in China, highlighting its emergence and potential risk to previously unaffected avian populations. Urgent enhanced surveillance and biosecurity measures are strongly recommended to prevent further spread within duck flocks.