Abstract: 【Objective】 The objective of the study is to illustrate the viremia of ducks challenged with duck hemorrhagic ovaritis virus (DHOV-HB Strain) , to gain insight into the pathogenesis of DHOV and provide data for diagnosis and vaccine development.【Method】A group of twenty-four 250-day-old Peking ducks with implanted chip were infected with 100-fold diluted DHOV-HB (3×10⁴ELD₅₀) orally, 15 ducks as negative control were kept in isolation unit under the same condition, clinical signs were observed daily. On 1-10 day post inoculation (DPI), 10 serum samples were collected from each group via wing vein daily for virus-isolation and antibody determination (select the same duck as possible). The serum samples of 1-10 DPI were inoculated into 6-day-old SPF chicken embryos via yolk-sac route. Five SPF chicken embryos were inoculated for each sample at the inoculum of 0.1 mL per embryo. Then they were hatched at 37℃ further. The chicken embryos were observed regularly twice a day. Reap and count the death chicken embryos during 24-168 h in time. Then the death chicken embryos were cut into small pieces, and then centrifuged the grinding homogenate. The viral nucleic acid was detected by RT-PCR in the supernatant. If there are more than one (including one) death chicken embryos, and the nucleic acid testing was positive, then it was concluded that virus isolation was positive. Using the classical neutralization test method to detect the serum antibody of 4-10 DPI, 5 SPF chicken embryos were inoculated for each serum dilution. The inoculation method and criteria of embryos’ specific death were performed as previously described. The determination standards are as follows: results with serum protect more than 80% (4/5) chicken embryos, the serum antibody was recognized as positive, 20%-60%(1/5-3/5) were as doubtful, and 0%(0/5) as negative.【Result】The viremia and antibody responses were closely related after infection with DHOV. The viremia could be detected as early as 1 DPI, peaked at 1-3 DPI. By this time, the positive isolation rate of serum were all 100% (10/10). On 4-6 DPI, the positive isolation rate of serum began dropping which were 90% (9/10), 70% (7/10), and 30% (3/10), respectively, and no virus was recovered anymore on 7-10 DPI. The results of the neutralization test indicated that there were low titer antibodies in the serum while the virus isolation positive rate showed a decreasing trend on 4 DPI, showed up as the death time of the embryos postponed while the antibodies of the inoculated ducks were all negative temporarily. It was 80%(8/10) negative, 20%（2/10） doubtful on 6 DPI , 70% (7/10) positive, 10% (1/10) negative, 20% (2/10) doubtful on 7 DPI, 90% (9/10) positive 10% (1/10) doubtful on 9 DPI, and the antibodies of the inoculated ducks were all positive on 10 DPI. Virus isolation (1-10d) and antibody test (4-10d) results were all negative in the negative control ducks. 【Conclusion】The duration of viremia stage of ducks infected with DHOV-HB was short, the virus was recovered in 100% (10/10) on 1-3 DPI, decreased on 4 DPI and disappeared on 7 DPI. The antibody-positive rate was 70% (7/10) on 7 DPI and reached 100% (10/10) on 10 DPI. Further analysis showed that the quickly absence of viremia was closely related to specific antibody response. The antibody-positive rate was 70% (7/10) on 7 DPI and reached 100% (10/10) on 10 DPI.

Key words: ducks, duck hemorrhagic ovaritis, Tembusu virus, viremia