| Duck Tembusu virus disease(DTMUVD)is an acute,highly contagious disease caused by Duck Tembusu virus(DTMUV).It is characterized by a severe decrease in egg production in laying ducks and neurological symptoms in young or adult ducks and death may occur in severe cases.has caused huge economic losses to the duck farming industry.In order to screen Chinese herbal medicine against DTMUV and explore its antiviral effect,this study selected Chinese herbal medicines with antiviral activity and immune enhancement and relatively low price as the test drugs,DTMUV strain isolated and purified from Sansui County was used as the virus solution,and Chinese herbal medicines with anti-DTMUV activity were screened through the study of anti-DTMUV effect in vitro.This study also studied the intervention effects of anti-DTMUV Chinese herbal medicines in ducklings infected with DTMUV,and the effects of anti-DTMUV Chinese herbal medicines on the immunity of laying ducks inoculated with DTMUV vaccine.The main contents are as follows:1.Screening of anti-DTMUV single Chinese herbal medicine in vitro12 water extracts were prepared by decocting method,and the maximum safe concentrations of 12 drugs on Duck embryo fibroblasts(DEF)were determined by CCK-8 method.The Cytopathic Effect(CPE)method and CCK-8 method were used to select the optimal concentrations of 12 drugs against DTMUV on DEF.12 drugs with optimal concentration were prepared to evaluate their effects on morphology,viral inhibition rate,viral titer and viral load of DEF infected with DTMUV.Results showed that optimal anti-DTMUV concentrations of Herba Houttuyniae(HH),Epimedium Herb(EH),Lonicerae Japonicae Flos(LJF),Radix Isatidis(RI)Dryopteris crassirhizoma Nakai(DCN),Astragalus membranaceus(AM),Wine-processed Scutellaria Baicalensis(WSB),Herba Artemisiae Scopariae(HAS),Radix Glycyrrhiza(RG),Vingar-proessed Schisandra Chinensis(VSC),Fructus Forsythiae(FF)and Paeoniae Radix Alba(PRA)could reduce the CPE of DEF infected with DTMUV and have different inhibition rates on DTMUV at the optimal concentration,among which WSB had the most significant effect.The virus titer of DTMUV could be significantly decreased by EH,PRA,RI,AM,HAS,RG and FF(P<0.05).RI,WSB and VSC could significantly reduce the viral load of DTMUV in DEF(P<0.05).In conclusion,RI,WSB and VSC had obvious effect against DTMUV in DEF,which could provide some references for the selection of drugs for the prevention and treatment of DTMUV.2.Intervention effects of RI,WSB and VSC on ducklings infected with DTMUV150 7-day-old duckings with negative DTMUV antibody were divided into 5groups,including blank control group,viral control group,RI group,WSB group and VSC group.The duckings were fed until 15 days of age.All the groups were challenged with DTMUV except blank control group.The survival rate of clinical symptoms in each group was observed and recorded.At 3,6,9 and 12 days after challenge,pathological changes,immune organ index,serum Ig A,Ig G,Ig M,IL-2,IL-4,IL-6,IFN-γ content and tissue viral load were detected.The results showed that the virus control group presented typical clinical symptoms such as neurological symptoms and death,and the survival curve was significantly different from the blank control group(P<0.05).The clinical symptoms were not obvious and no death occurred in the three treatment groups.The three treatment groups could reduce the tissue lesions to varying degrees,while the virus control group showed yellowing and bleeding liver,marbled and enlarged spleen,pericardial effusion or "armor heart",meningeal congestion and bleeding,pale and bleeding kidney.The body mass of virus control group was significantly lower than blank control group on days 6 and 9(P<0.05),the spleen index was significantly higher than blank control group during the test period(P<0.05),and the thymus index on days 6 and 9 and bursa index on days 9 and 12 were significantly lower than blank control group(P<0.05).The abnormalities of body mass and immune organ index induced by DTMUV could be regulated in the three drug groups to different degrees,and the body mass of RI and VSC groups were significantly higher than virus control and blank control group on day 12(P<0.05).The contents of IL-2 in early stage and Ig A,Ig M and IL-4 in middle and late stage of virus control group were significantly lower than blank control group(P<0.05),and the contents of IL-6 in days 3 to 9 were significantly higher than blank control group(P<0.05),while the contents of Ig A,Ig M,IL-4 and IL-2 in three drug administration groups were increased to varying degrees.In addition,RI and WSB groups could reduce the overexpression of IL-6 caused by virus infection,and the Ig G content of RI group on day 3 was significantly higher than other groups(P<0.05).The heart,liver,spleen and brain tissues of the virus control group were continuously infected during the experiment.The viral loads of the spleen and liver of the three treatment groups were significantly lower than virus control group at day 3,9 and 12(P<0.05),and the viral loads of the heart and brain were significantly lower than virus control group at day 9 and 12(P<0.05).In conclusion,RI,WSB and VSC could relieve the body damage and immunosuppression caused by DTMUV infection,and reduce the amount of tissue toxicity and mortality of duckling.In addition,RI and VSC could also promote the weight gain of ducklings,and RI and WSB played an anti-inflammatory role,and RI showed more obvious immune enhancement effect and organ repair effect,which could be an alternative drug for the clinical treatment of DTMUVD.3.Effects of RI,WSB and VSC on laying ducks vaccinated with DTMUV vaccine100 34-week-old DTMUV antibody negative laying ducks were divided into 5groups: blank control group,vaccine control group,RI group,WSB group and VSC group.After 7 days of feeding,DTMUV vaccine was inoculated in all groups except blank control group,and the three drug groups were orally given the corresponding Chinese herbal water extract every day.The mortality rate of each group was observed and recorded daily.DTMUV antibody in serum was detected at days 7,14 and 21,and the laying rate was calculated weekly.The results showed no deaths in each group during the test.The serum antibody locking rates of the three drug groups were continuously higher than vaccine control group,and the antibody blocking rates of WSB and VSC groups were significantly different from vaccine control group on day21(P<0.05).The laying rates of vaccine control group and VSC group at week 2 were significantly higher than other groups(P<0.05),the laying rate of vaccine control group at week 3 was significantly lower than blank control group(P>0.05),and the laying rates of the three drug groups were significantly higher than vaccine control group and blank control group(P>0.05).In conclusion,continuous oral administration of RI,WSB and VSC aqueous extracts could enhance the immune effect of DTMUV vaccine on laying ducks,and improve the laying rate.VSC had better effect at the same time,which could be an alternative drug for DTMUV immune enhancer.In conclusion,the anti-DTMUV effects of RI,VSC and WSB were more prominent than other drugs in DEF.After the intervention of ducklings infected with DTMUV,these three drugs could relieve the body damage and immunosuppression,reduce the amount of tissue toxicity and duckling mortality,and the effect of RI was better.The three drugs could also improve the DTMUV antibody level and egg production rate of laying ducks,and the effect of VSC was better.This study could provide some reference for clinical prevention and treatment of DTMUVD. |
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