A septicemic outbreak in southern Taiwan duck farms in 2014 resulted in high mortality of ducklings. Samples from oral or cloacal sites of a®ected Muscovy and Pekin ducks were collected and the identity of the¯eld isolates was con¯rmed using Riemerella anatipestifer (RA) 16S rRNA and outer membrane protein A (OmpA)-speci¯c primers in polymerase chain reactions (PCR), with 15 isolates found positive for both 16S rRNA and OmpA. Detection of both the 16S rRNA and OmpA genes could be a rapid PCR test for RA. Serotyping of the isolates using gel-di®usion precipitin test identi¯ed serotypes 1, 4, 6, 17, and 19 while a number of isolates were unidenti¯able. Sequence analysis of the OmpA gene found high identity (99.0-99.7%) among isolates in Taiwan. These results indicate that RA remains as a signi¯cant cause of duck septicemic disease in southern Taiwan.
IntroductionRiemerella anatipestifer (RA) infections can lead to high mortality in ducklings. Inactivated vaccines against RA are commercially available, but they fail to provide cross-protection against various serotypes. We have previously demonstrated that a subunit vaccine containing recombinant outer membrane protein A (rOmpA) antigen of serotype 2 formulated with CpG oligodeoxynucleotides (ODN) as the adjuvant was able to stimulate both humoral and cellular immunities.Material and MethodsIn the present study, thirty healthy 7-day-old Pekin ducks were randomly assigned to three equal treatment groups: rOmpA-vaccinated, rOmpA + CpG-vaccinated, and control. Vaccine was injected intramuscularly and a booster dose of the same vaccine was given two weeks after primary immunisation. The long-term antibody response and cross-serotype reaction of this vaccine were evaluated in ducks.ResultsCompared to ducks immunised with rOmpA alone, ducks immunised with rOmpA + CpG ODN had significantly (p < 0.05) increased serum antibody titre from two weeks until nine months after primary immunisation. In addition, expression of cytokines including interferon (IFN)-α, IFN-γ, interleukin (IL)-6, and IL-12 was significantly (p < 0.05) enhanced in PBMC of ducks immunised with rOmpA + CpG ODN two weeks after primary immunisation. Antibodies from ducks immunised with the rOmpA + CpG ODN vaccine could also detect RA serotypes 1 and 6 in Western blot analysis.ConclusionCombination of rOmpA and CpG ODN could be a feasible strategy for developing a subunit RA vaccine with long term and broader-ranging protection.
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