ABSTRACT
To investigate the relationship of the variation of virulence and the external capsid proteins of the pandemic duck hepatitis A virus type 1(DHAV-1) isolates,the virulence,cross neutralization assays and the complete sequence of the virion protein 1(VP1) gene of nine virulent DHAV-1 strains,which were isolated from infected ducklings with clinical symptoms in Shandong province of China in 2007-2008,were tested.The fifth generation duck embryo allantoic liquids of the 9 isolates were tested on 12-day-old duck embryos and on 7-day-old ducklings for the median embryonal lethal doses(ELD50s) and the median lethal doses(LD50s),respectively.The results showed that the ELD5s of embryonic duck eggs of the 9 DHAV-1 isolates were between 1.9 × 106/mL to 1.44 × 107/mL,while the LD50s were 2.39 × 105/mL to 6.15 × 106/mL.Cross-neutralization tests revealed that the 9 DHAV-1 isolates were completely neutralized by the standard serum and the hyperimmune sera against the 9 DHAV-1 isolates,respectively.Compared with other virulent,moderate virulent,attenuated vaccine and mild strains,the VP1 genes of the 9 strains shared 89.8％-99.7％ similarity at the nucleotide level and 92.4％-99.6％ at amino acid level with other DHAV-1 strains.There were three hypervariable regions at the C-terminus(as 158-160,180-193 and 205-219) and other variable points in VPI protein,but which didn't cause virulence of DHAV-1 change.
ABSTRACT
The levels of the antibody response against,classic swine fever (CSF) vaccine were measured by blocking ELISA at different time for pigs vaccinated with CSF vaccine (CSFV group,n= 3),pigs inoculated with porcine eircovirus type 2 (PCV2) and with CSF vaccine two weeks later (when PCV2 viremia was detected by PCR,PCV2/CSFV group,n=3),or inoculated with both CSF vaccine and PCV2 at the same time (CSFV/PCV2 group,n=3),respectively.And distribution of genome or antibodies specific to PCV2 of the PCV2 infection group,PCV2/CSFV group and CSFV/PCV2 group were also detected by indirect ELISA or PCR,respectively.The results showed that experimental infection of PCV2 was successful.In pigs inoculated with both PCV2 and CSF vaccine,the antibody response to CSF vaccine was significantly lower than that of animals treated with CSF vaccine vaccination alone at 52 days postinoculation (DPI).The average titers of antibodies against CSFV in animals of CSFV group were obviously higher than those of the PCV2/CSFV or CSFV/PCV2 group at 49 and 52DPI,respectively.The positive rate of antibodies against CSFV in pigs of CSFV group was 100% in comparison with that of animals inoculated with PCV2 and the vaccine (only 67%).The results suggested that the infection of PCV2 could suppress the antibody response to classical swine fever vaccine.