Epidemiologic Investigation On The Co-infection Of Immunosuppressive Virus And Study On Pathogenicity Of Duck Reovirus In Ducks

Avian influenza virus (AIV)，Avian metapneumovirus (aMPV)，Duck Reovirus (DRV),Reticuloendotheliosisvirus (REV), Duck Circovirus (DuCV), Infectious bursal disease virus(IBDV) are common immunosuppressive diseases in ducks which can induce apoptosis oflymphocytes of central lymphoid organs, cellular immunity and humoral immunity, resultingin immunosuppression, death and elimination.The samples of397sick ducks and200clinically healthy ducks were collected fromdifferent areas of Shandong province, then dot blot hybridization was used to detect Avianinfluenza virus (AIV), Avian pneumovirus (aMPV), Duck reovirus (DRV), Duck circovirus(DuCV), Infectious bursal disease virus (IBDV) and Reticuloendotheliosis virus (REV). Theresults show that the detection rates of the six pathogens of sick ducks are57.43%(H9N2),51.39%(aMPV),38.54%(DRV),39.55%(REV),29.47%(DuCV),10.58%(IBDV)respectively, and co-infection is existed. The ratios of the dual infection and triple infectionare26.20%,18.89%, among which the detection rates of aMPV and H9N2or REV and DuCVare higher than others. The ratios of the six pathogens of200samples of clinically healthyducks are7.00%(H9N2AIV),19.5%(aMPV),15.5%(DRV),10.5%(REV),24.00%(DuCV),9.00%(IBDV) respectively, and negative and single infection are40.00%and28.00%, theratios of co-infection is only32.00%. Moreover dual infection is dominant. In conclusion, theco-infection of the immunosuppressive viruses has already been universal and it is one of themost important epidemiologic factors of morbidity and poorgrowth now.Thirty ten-old-day cherry valley ducklings randomly divided into two groups. Fifteenducklings were each inoculated intravenously with0.2mL of the isolated reovirus.Meanwhile, the uninfected controls were inoculated with0.2mL of sterile physiologicalsaline in the same way. The groups were housed in two separated isolation units. Ducklingswere regularly observed for clinical signs, and on day3,6,9,12and15post inoculation, thefollowing procedures were conducted for each group. Three ducklings were randomlyselected from each group, then blood was collected to separate serum and carry out the bloodbiochemical tests and examine the ratio of CD4+/CD8+by flow cytometry. The serum was collected to examine IL-6, IFN-γ levels by ELISA kits, respectively. While clinicalobservation was proceed per3days over a period of15days, when the experiment wasterminated. Moreover, postmortem changes were also recorded and tissue pieces such as liver,spleen, lung, etc. were collected to histopathological observation. Additionally, whole bodyweight, relative weights of immune organs, such as spleen, thymus and bursa of Fabriciuswere also investigated at day3,6,9,12and15post inoculation.At day3post inoculation, all of15ducklings inoculated with reovirus showed depressed,huddled together, and reduced food and water intake. Ducklings appeared smaller than theuninfected group. At postmortem examination, on day3PI, enlarged spleen with dark redbecause of haemorrhages and more visible yellow focal necrosis were observed.Hispathological observation showed the vasculaturs and immune organs such as bursa ofFabricius and spleen performed significantly microscopic changes. Lymphocyte depletion wasevident with reticular fiber visualized in bursa of Fabricius and spleen. The granulomastructure and necrotic foci were seen in the spleen and the artery of spleen showedhomogenizing, swollen, sparsely, vacuolar degeneration in vessel wall, even occlusive.Routine blood indexes of WBC, RBC, HGB overall showed a increase. On day9,12,15PI,WBC of test group showed a significantly increase compared with the control (P<0.05).Meanwhile, HGB always showed a significantly increase compared with the control (P<0.05).The BUN showed a increase during the period of experenmental observation, significantlyhigher than those in the control group on day3,9,12PI (P<0.05). The ALB of serum of testgroup showed significantly lower than those in the control group only on day3PI (P<0.05),then rised since at day9PI. Moreover a non-significant increase was observed in the TP.Indirectly Flow cytometry results showed a significantly decrease in the ratios of CD4+/CD8+compared with controls on day6,9,15PI. Although it increased later, but the ratio ofCD4+/CD8+still remains lower than that of the control group. The regularity of IL-6andIFN-γ levels showed as same as CD4+/CD8+and were significantly lower than those ofcontrol group on day9PI. Results of immune organ indexes showed that spleen and bursa ofFabricius also were significantly lower than control group on day6PI, but higher than controlgroup on day15PI. However, altered spleen index were always larger than those ofuninfected. In conclusion, immune organs were the objective organs after infected with duck reovirus and the serious depletion of immune organ lymphocyte, leading toimmunosuppression.