| A kind of laying egg drop symptom in duck occurred in farms in southeast China since april,2010.This disease was quickly spreading in the north China in the end of year.It infected laying ducks,breed ducks and even young maet-type ducks.The feed intake of infected ducks was droped down obviously,clinical symptoms appeared green diarrhea,losing weight,encephalitis,and nerve disordered,ataxia.The research indicated that the pathogen causing the disease belongs to a kind of yellow virus,and is Tembusu virus.This kind of disease not only spreaded in ducks,but also in young meat-type geese,sparrows,and pigeon races.There were no commercial vaccines for Tembusu virus until now.The main target of this study was by comparing the pathogenicity of different Tembusu virus(TMUV)strains from geese,ducks and chickens,to provide the reference for the Tembusu virus vaccine strain selection.Test Ⅰ The reproduction of different original Tembusu virus in suckling mice brainsIn order to increase the quantity of the six different original Tembusu virus,three-day-old suckling mice were infected by intracerebral(i.c.)injection with 15μL of virus suspension which kept in our lab and double diluted.After three to five passages in suckling mice,we collected the brains when the clinical signs were steadily observed in 5-6 days post inoculation.The six different original Tembusu virus were tested by RT-PCR and measured TCID50 in DF-1.In order to compare the pathogenicity of different Tembusu virus(TMUV)strains from geese,ducks and chickens,3-day-old ICR mice which were 3-day-old were divided into 7 groups and infected intracerebrally with 1.5×104.0 TCID50 per mice.According to the clinical signs and mortality,we could judge the pathogennicity of the six virus strains from different sources.The left of the virus were stored in-20 ℃ for the next experiences.In conclusion,the TCID50 was as follows:JS804,106 75 TCID50;SQ260,107.67TCID50;JS808,107.5TCID50;YC508,107.5TCID50;NJ705,107.5TCID50;WJ901,106.75 TCID50.The pathogenicity selected from highest to lowest was as follows:JS804 = SQ260>YC508>JS808>WJ901>NJ705.Test Ⅱ Comparision pathogenicity of different original Tembusu virus for Cherry Valley ducksIn order to compare the pathogenicity of different Tembusu virus(TMUV)strains from geese,ducks and chickens,5-day-old 56 Cherry Valley ducks which were divided into 7 groups,8 ducks per group.The ducks arrange of 1-6 groups were infected intramuscularly with 0.4 mL,0.4 ×106.0 TCID50 per duck of six challenge virus stocks.The six challenge virus including two strains separeted from geese,named JS804 and SQ260;two strains separated from ducks,named JS808 and YC508;two strains separated from chickens,named NJ705 and WJ901,and the 7th group served as the control,injected with PBS at the same methods.The clinical signs,weight gain,mortality,macroscopic and microscopic lesions,virus loads in serum of 1,3,5,7,11 and 14 days post inoculation and serum antibody titers were examined.The results showed that all of these viruses could cause the young ducks sick,but the clinical signs differed with the different spices-original virus strains.All the experimental groups lose in weight gain compared to the control markedly,but there was no obvious distinctions in weight gain between the infected groups.While the treated groups of goose-derived and duck-derived strains(from geese and ducks)showed more serious in clinical signs,higher relative expressions of virus loads in serum than that from chickens.The mortality of waterfowl groups closed to 37.5%,while the most mortality of chicken groups was 12.5%.The serum antibody titer of group JS804 was higher and appeared earlier than others.The conclusion was that the pathogenicity of goose-derived and duck-derived TMUV were more acute than chicken-derived and JS804 could be chose for TMUV inactivated vaccine strain to protect from infection.Two chicken-derived TMUVs could be served as attenuated vaccine strains for option. |
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