A Study On The Pathogenicity Of Japanese Encephalitis Virus To Ducklings

Japanese encephalitis virus(JEV)is an enveloped,single positive stranded RNA virus,belonging to the Flaviridae Genus in the Flaviridae Family,and has a significant impact on animal husbandry and public health as a zoonotic pathogen.JEV is transmitted by mosquito vectors and birds and pigs are the amplifying hosts of JEV.Domestic ducks are susceptible to JEV infection.Previous studies suggest that experimental infection of newly hatched domestic ducklings via subcutaneous injection of JEV results in the stunted growth and death,suggesting the potential pathogenicity of JEV in domestic ducklings.To evaluate the potential pathogenicity of JEV natural infection in domestic ducklings,the following experiments were conducted.To survey the prevalence of JEV in domestic ducks,serum and died duckling samples were collected from a duck farm in Jiangsu province.Analysis of JEV antibodies by enzyme-linked immunosorbent assay in the serum samples collected from egg-laying ducks indicated that out of 20 samples,15 were seropositive for JEV antibodies.The seropositive rate of JEV antibodies was as high as 75 %(15 /20).Detection of JEV gene by RT-PCR in the dead ducklings suggested that among 19 samples,one was positive and two were weakly positive for JEV presence.Sequence analysis of the JEV gene fragment amplified by RT-PCR showed that the JEV detected in the dead ducklings belonged to genotype I of JEV.These data indicated the prevalence of JEV in the duck farm examined.In order to evaluate the potential pathogenicity of JEV to domestic ducklings,JEV natural infection of domestic ducklings was simulated via JEV-infected Culex pipiens mosquito bite.Infection of domestic ducklings at day 2 post-hatching via JEV-infected mosquito bite resulted in viremia and non-characteristic clinical signs and caused 30 %(6 /20)of mortality.Some of the ducklings died suddenly with a neurological sign of opisthotonos.The multifocal lymphohistiocytic perivascular cuffs and lymphohistiocytic meningitis that are the hallmark of JEV encephalitis were macroscopically observed in the affected duckling's brains.JEV was detectable in the cytoplasm of neuronal cells of the affected duckling's brains by immunohistochemical assay and recovered from the affected duckling's brains by virus isolation on BHK-21 cells.The gene sequence of the recovered virus was identical to that of JEV strain used for infection of Culex pipiens mosquito.These observations indicated that JEV infection via mosquito bite caused mortality associated with viral encephalitis in newly hatched domestic ducklings,demonstrating the potential pathogenicity of JEV in domestic ducklings.In conclusion,the data obtained from this study demonstrated that JEV was prevalent in domestic ducks and that JEV was pathogenic to domestic ducklings.Domestic duck farming is a popular business in southern China,where ducks closely contact with humans and mosquitoes,which may facilitate JEV transmission and thereby having an impact on ducking breeding and public health.Future epidemiological survey of JEV presence in domestic ducks is recommended.