Liu Xiu-fan

A candidate inactivated chimeric vaccine PCV1‐2 constructed based on PCV1 and PCV2 isolates originating in China and its evaluation in conventional pigs in regard to protective efficacy against PCV2 infection

A chimeric PCV1‐2 clone containing the PCV2 capsid gene cloned into the backbone of the nonpathogenic PCV1 genome was recently generated based on PCV2 and PCV1 strains isolated in China. The efficacy of this available candidate inactivated vaccine was evaluated by subjecting conventional pigs to intramuscular immunization with the inactivated chimeric PCV1‐2 virus, followed by challenge with wild‐type PCV2 strain. By 35 days post‐vaccination (DPV), all vaccinated pigs had developed seroconversion, having high indirect immunofluorescence assay (IFA) titers of antibody and neutralizing antibody against PCV2. By 21 days post‐challenge, gross and microscopic lesions of lymph nodes and lungs in non‐vaccinated but challenged pigs were significantly more severe than those found in the vaccinated group. PCV2 viral copy loads detected in the tracheobronchial lymph nodes or serum samples of vaccinated pigs were significantly smaller than those in non‐vaccinated but challenged pigs (P≤ 0.05). The results suggest that inactivated PCV1‐2 is effective in inducing protective immunity against PCV2 infection.

Effect of recombinant fowlpox virus expressing chicken interferon-γ on active immunity induced by avian influenza vaccines of H5 subtype in chickens

To evaluate the potential adjuvant effect of chicken interferon-γ (IFN-γ) expressed by recombinant fowlpox virus (rFPV–IFN-γ), SPF chickens and commercial chickens with (MAb + ) and without (MAb − ) maternal antibodies were immunized with rFPV–IFN-γ plus either H5 subtype avian influenza vaccine based on recombinant fowlpox virus (rFPV–HA) or conventional inactivated vaccine. In the assay of humoral responses, rFPV–IFN-γ plus vaccines induced a slightly lower titre of haemagglutinin inhibition (HI) antibody response than either rFPV–HA or inactivated vaccine alone, in both MAb − and MAb + chickens. As for protective efficacy, the combinations of rFPV–IFN-γ and both vaccines induced 95–100% protection against lethal challenge with highly pathogenic avian influenza virus in SPF chickens and MAb − chickens, which were equal to those induced by either vaccine alone. However, immunization of MAb + chickens with 10 6 pfu rFPV–HA plus 10 5 pfu rFPV–IFN-γ showed higher protection efficacy (33.5%) than that (11.4–15.8%) induced by treatments with other dosage combinations. These findings show that IFN-γ expressed by recombinant fowlpox virus could not promote HI antibody response induced by H5 avian influenza vaccines in chickens. The results also suggest that rFPV–IFN-γ enhances the protection of chickens in a dose-dependent and immune status-dependent manner.

Modification of the full-length cDNA clone of Newcastle disease virus isolated from an outbreak in the goose

A 6.5-kb specific fragment containing the T7 promoter and the transcription vector was excised from the full-length cDNA clone of the Newcastle disease virus (NDV) strain ZJI of goose origin, and thereafter it was self-ligated to form a high quality plasmid for mutagenesis. Site-directed mutagenesis was used for inserting three additional G nucleotides (nts) into the region between the T7 promoter and the leader sequence of the NDV genome. RT-PCR was employed to amplify the F/HN gene fragments, and then they were ligated by the shared restriction enzyme BsmBI. Finally, the corresponding fragment in the mutant full-length cDNA was substituted with the new one. The sequencing results showed that the three additional G nts were successfully inserted and the mutant nts in the full-length cDNA were corrected. This study lays a good foundation for research on the reverse genetics of NDV strain ZJI.