Study On Immunopathology Of Duckling Infected With Streptococcus Isolates From Ducks

6-day old ducklings were inoculated with streptococcus.They were divided into six groups and respectively inoculated by I.V.,HYPO,I.M.,oral,web-foot and joint cavity. The group infected by I.V.was given three kinds of doses at different levels.Clinical symptom,disease rate and death rate of infected duckling were observed.Peripheral blood cells T_ANAE⁺,erythrocyte rosette of C_3b receptor and immune complex were detected in inoculated ducklings at 4^th,7^th,14^th,21^st,28^th day post infection.Ducklings were forced to death at 28^th day,pathological change of organs were observed,bacterium of liver was isolated,and quantity of spleen IgY positive cells and index of immune organ were detected.The results show that disease rate of duckling infected by HYPO was 60%,death rate was 10%.Disease rate of duckling in I.M.group was 60%,none was dead.However, disease rate of duckling inocuated by web-foot was 10%,none was dead either.Ducklings infected with I.V.high dose acutely dead of bacterial embolism at 18 h post infection.In I.V.group with moderately dose,disease rate was 20%,none was dead.Hispathological change of duckling in HYPO and I.M.group were:endocarditis,nerosis area in liver, spleen and kidney.Peripheral blood cells T_ANAE⁺ of duckling in HYPO group had decreased at 4^th,7^th, 14^th,21^st,28^th day.In I.M.and web-foot group,the value of T_ANAE⁺ had declined since 4^th day,in oral group,its value had decreased at 28^th day.And in ducklings inocuated with moderately dose,T_ANAE⁺ had declined at 4^th,7^th day.The rate of RBC-C_3bRR of ducklings in HYPO group had decreased at 4^th,7^th day, and rate of RBC-ICR had rised at 7^th day.Rate of RBC-C_3bRR of ducklings infected by web-foot had decreased since 7^th day,and the rate of RBC-ICR had increased.In the I.V. group with moderately dose,the rate of RBC-C_3bRR had declined at 4^th,7^th day,and the rate of RBC-ICR had increased at 4^th,7^th,14^th,21^st,28^th day.In the I.M.group,rate of RBC-C_3bRR had increased at 14^th,21^st,28^th day,the rate of RBC-ICR had rised since 7^th day.However,rate of RBC-C_3bRR of ducklings in oral group had increased at 4^th,21^st, 28^th day,and rate of RBC-ICR had rised at 21^st,28^th day.The quantity of spleen IgY positive cells of ducklings in HPYO and I.M.group had declined,index of spleen and thymus in these group had rised.And the index of bursa and thymus of ducklings infected by web-foot had increased.Bacterium isolation could be obtained almost in all groups except in oral one,and the isolation rate had declined day by day.All of index in duckling infected by I.V.and joint cavity show no significant difference against contrast group.The result shows that HYPO and I.M.are optional pathway for ducklings infected with streptococcus by artifical.Cell immunity and humoral-mediated immunity of infected ducklings were depressed at different levels through HYPO and I.M..