Isolation And Partial Bio-characteristics Of Novel Virus Causing Duck Dwarfism Disease

The outbreak of animal infectious diseases was one of the main reasons causing negative impacts in livestock and poultry industry.Pre-existing pathogens change their pathogenicity and host ranges through gene variation and recombination often,and accordingly bring great challenges on diseases prevention and control.Emerging of novel pathogenic causatives constantly results in more difficulties in prevention and control of infectious disease in livestock and poultry.In recent years,A duck infectious diseases,characterized as short-beak,exposed-tongue,growth retard broke out in China.The disease occurred firstly in Peixian in Jiangsu province,and then spread to other area in the province of Anhui and Shandong.The disease caused huge of economic losses in the meat and duck industry in China so far.Epidemiological survey shows that cherry valley duck is most susceptible to this emerging infectious disease,the incidence ranged from 0.1%to 0.5%in the beginning,and increased gradually to 10%to 15%recently.In order to identify the pathogenic caustives of the new infectious diseases,the organs and tissues were collected from ill duck in Dangshan in Anhui province and homogenized,and then the supernatant were passed through 0.22 micron filter,inoculated into the allantoic cavity of 11-day-old SPF embryonated chicken eggs.The chicken embryos were killed during 24 to 36 hours post inoculation,and showed hyperemia in skin and thickness of the chorioallantoic membrane.The virus titers in allantoic fluid reached to 10^7.5ELD₅₀/100ul.The virus was very sensitive to ether and chloroform,but could not agglutinate chicken erythrocytes.The virus could not be determined as any known viruses by PCR or RT-PCR using the primers designed according to known avian viruses.The virus might be one of novel emerging virus and was named as Anhui2.In order to determine the taxonomic status of the virus,the virus was purified by the sucrose density gradient centrifugation method and observed under electron microscopy.Anhui2 was a spherical or oval,70-100nm of diameter,and enveloped virus.The nucleic acids of the purified virus were extracted and digested with different nuclease respectively.The virus nucleic acids could not be degraded by DNase but could be degraded by RNase,which indicated that the virus was a RNA virus.Both of cherry Valley duck and SPF duck could be infected by Anhui2,The growth of Cherry Valley ducks infected with the virus were retard significantly when compared with the control ducks.Importantly,Anhui2 was able to be spread among ducks and caused contact ducks growth retard.The virus was recovered from the nasal turbinate,glandular stomach,thymus,bursa of Fabricius,femoral head,though the virus titers is low.In this study,Anhui2 was isolated and was proved to cause duck growth retard.According to the organs where the virus replicated,the virus might damage the duck's immune system and result in immunosuppression.The threat of this new virus on the duck industry should not be ignored.The data in this study provided partial biological characteristics of the novel emerging duck virus,and those basic knowledges would be useful for the prevention and control of the disease caused by the virus.