Dynamic Changes Of Some Immune Indicators Of Tembusu Virus-infected Ducklings

Tembusu virus(TMUV) is an emerging virus of of Flavivirus family. The disease outbroke in 2010, characterized by acute anorexia, retarded growth, neurological dysfunction and severe egg production drop, and caused great financial loss to duck industry(Li et al., 2014; Sun et al., 2014b). Although inactivated and live attenuated vaccines against duck Tembusu virus(DTMUV) have been successfully developed(Li, et al. 2014; Sun, et al. 2014), this virus remains an important cause of duck morbidity and mortality within duck farms in China(Cao, et al. 2011; Sun, et al. 2014). Studies have shown that house sparrows and mosquitoes carrying the virus greatly contribute to the spread of the virus to other species(Tang, et al. 2015; Tang, et al. 2013). The disease was originally called duck hemorrhagic ovaritis(DHO), but further studies have shown the virus to be an emerging member of the Flavivirus family(Cao, et al. 2011). Currently, almost all species of ducks, shelducks in particular, are susceptible to DTMUV((Tang, et al. 2015; Yan, et al. 2011). The clinical characteristics of duck Tembusu virus disease include acute anorexia, retarded growth, neurological dysfunction, and severely lowered egg production(Cao, et al. 2011). Ovarian hemorrhaging and necrosis, liver degeneration and swelling, endocardium and epicardium hemorrhaging, and spleen necrosis have been observed within autopsies(Cao, et al. 2011; Sun, et al. 2014; Yan, et al. 2011).Ducks of different age have different susceptibility to Tembusu virus: ducklings and laying ducks are most susceptible to TMUV(Cao et al., 2011a). Sun et al conduct their research to investigate the effect of host age on the outcome of TMUV infection. And the result indicates that susceptibility to TMUV infection were age-related with younger ducks being more susceptible. To investigate the dynamic changes of immunity function indexes in serum of ducklings artificially infected with the duck Tembusu virus(DTMUV), the blood samples were collected at different days from the ducklings post intravenous inoculation wit h the DTMUV at 5-day-old, 10-day-old and 25-day-old, respectively, and subject to detection of Ig A, IgG, Ig M and IL-2, IL-4, IL-6, IFN-? in the ducklings serum. The results showed that the titers of the three immunoglobulins were significantly higher in infected groups than that in the control group, indicating that humoral immunity played a major role in anti-virus infection. However, all the levels of IL-2, IL-4, IL-6 and IFN-? in serum of ducks infected at 5-day-old were lower than that in control groups. Although the IL-2, IL-4 and IL-6 increased in varying degrees in serum of ducks infected at 10-day-old, the IFN-? was still lower than that in the control group. Eventually, the IL-2, IL-4 IL-6 and IFN-? in serum of ducks infected at 25-day-old were significantly higher than that in control group in a week post artificial infection(p?0.05). In conclusion, the cellular immune systems of 5-day-old ducks are inhibited by DTMUV in some degrees, and this inhibition was vanishing in an age dependent manner, result in the cellular immune systems gradually play a more important role for the anti-virus infection.Choose one experiment group above- 5-day-old ducklings,studying its dynamic changes of immune system after TMUV infection: the tissue samples were collected at different days from 5-day-old ducklings post intravenous inoculation with the DTMUV at 5-day-old, and subject to histologic examination, viral antigen detection and apoptosis assay. Microbiology lesions and indices of immune organs showed that bursae, spleens, and thymuses were seriously damaged when ducks infected with DTMUV. The spleen showed lymphoid cell depletion on 4 days post inoculation, which became most severe at 6 dpi. In surviving ducks, lymphocyte regeneration began on 8 dpi, and by 16 days after artificially infected DTMUV, the structure of spleen almost restored to normal. In thymus, large necrosis areas and cells swollen have been perfectly obvious at 4 dpi; by 6 days after infection, vein thrombosis became extremely severe and the disintegration and necrosis of lymphocytic cells accompanied with cell vacuolation also became more evident; at 8 dpi, lesions in thymus was less severe; and the thymus has recovered fairly well by 16 days after infection. Bursa initially exhibited mild atrophy of fabricius nodes, and the histopathologic changes in the bursa of infected ducks increased to the maximum by day 6. Greater recover of the lymphoid cell density of bursa was observed at 8 dpi; till 18 days after challenge, most of the fabricius nodes looked normal. Viral antigen was detected by immunohistochemical stain. And apoptosis assay demonstrated that DTMUV indeed induces apoptosis on splenocytes, which have a negative impact on the immune functioning. In summary, TMUV can seriously damage the immune organs of ducklings, and this damage usually occurs in the early stages of infection, and shows recovering signs at 8 dpi.