Detection and clearance of a mosquito densovirus contaminant from laboratory stocks of Zika virus

BACKGROUND The Zika virus (ZIKV) epidemics that affected South America in 2016 raised several research questions and prompted an increase in studies in the field. The transient and low viraemia observed in the course of ZIKV infection is a challenge for viral isolation from patient serum, which leads to many laboratories around the world sharing viral strains for their studies. C6/36 cells derived from Aedes albopictus larvae are commonly used for arbovirus isolation from clinical samples and for the preparation of viral stocks. OBJECTIVES Here, we report the contamination of two widely used ZIKV strains by Brevidensovirus, here designated as mosquito densovirus (MDV). METHODS Molecular and immunological techniques were used to analyse the MDV contamination of ZIKV stocks. Also, virus passages in mammalian cell line and infecting susceptible mice were used to MDV clearance from ZIKV stocks. FINDINGS MDV contamination was confirmed by molecular and immunological techniques and likely originated from C6/36 cultures commonly used to grow viral stocks. We applied two protocols that successfully eliminated MDV contamination from ZIKV stocks, and these protocols can be widely applied in the field. As MDV does not infect vertebrate cells, we performed serial passages of contaminated stocks using a mammalian cell line and infecting susceptible mice prior to re-isolating ZIKV from the animals' blood serum. MDV elimination was confirmed with immunostaining, polymerase chain reaction (PCR), and analysis of the mosquitoes that were allowed to feed on the infected mice. MAIN CONCLUSIONS Since the putative impact of viral contaminants in ZIKV strains generally used for research purposes is unknown, researchers working in the field must be aware of potential contaminants and test viral stocks to certify sample purity.

Investigation on mosquitoes and mosquito-borne viruses in Dehong prefecture,Yunnan province,2007 and 2010 / 中华流行病学杂志

Objective To investigate the distribution patterns of mosquitoes and mosquito-borne viruses in Dehong prefecture,Yunnan province,China. Methods Mosquito samples were collected using the mosquito traps from five counties of Dehong prefecture on July,2007 and 2010. Mosquitoes were cell cultured for viral isolation,and positive isolates were identified using RT-PCR and sequence analysis. Results A total of 43 634 mosquitoes comprised of 29 species representing six genera were collected. Culex tritaeriorhynchus and Anopheles sinensis comprised 78.69% and 14.77% of the total. Six strains of viruses were isolated from the mosquito pools. RT-PCR and phylogenetic analysis revealed three strains from Cx. tritaeriorhynchus,identified as genotypeⅠJapanese encephalitis virus(JEV). One strain was identified from Cx. tritaeriorhynchus,as Getah virus (GETV). Two strains isolated from Cx. tritaeriorhynchus and Anopheles vagus were identified as Culex pipiens pallens Densovirus(CppDNV). Conclusion Cx. tritaeriorhynchus had been the major species of mosquitoes and mainly transmitting vector of mosquito-borne viruses in Dehong prefecture. GenotypeⅠJEV,GETV and CppDNV were the vectors causing transmission of mosquitoe-borne diseases in this area. Data from phylogenetic analysis showed that these newly discovered isolates seemed to have had close relationship with those viruses previously circulating in Yunnan and other provinces of China.

Investigation on mosquitoes and mosquito-borne viruses in Dehong prefecture,Yunnan province,2007 and 2010 / 中华流行病学杂志

Objective To investigate the distribution patterns of mosquitoes and mosquito-borne viruses in Dehong prefecture,Yunnan province,China. Methods Mosquito samples were collected using the mosquito traps from five counties of Dehong prefecture on July,2007 and 2010. Mosquitoes were cell cultured for viral isolation,and positive isolates were identified using RT-PCR and sequence analysis. Results A total of 43 634 mosquitoes comprised of 29 species representing six genera were collected. Culex tritaeriorhynchus and Anopheles sinensis comprised 78.69% and 14.77% of the total. Six strains of viruses were isolated from the mosquito pools. RT-PCR and phylogenetic analysis revealed three strains from Cx. tritaeriorhynchus,identified as genotypeⅠJapanese encephalitis virus(JEV). One strain was identified from Cx. tritaeriorhynchus,as Getah virus (GETV). Two strains isolated from Cx. tritaeriorhynchus and Anopheles vagus were identified as Culex pipiens pallens Densovirus(CppDNV). Conclusion Cx. tritaeriorhynchus had been the major species of mosquitoes and mainly transmitting vector of mosquito-borne viruses in Dehong prefecture. GenotypeⅠJEV,GETV and CppDNV were the vectors causing transmission of mosquitoe-borne diseases in this area. Data from phylogenetic analysis showed that these newly discovered isolates seemed to have had close relationship with those viruses previously circulating in Yunnan and other provinces of China.

Genetic and biological characterization of a densovirus isolate that affects dengue virus infection

Brevidensoviruses have an encapsidated, single-stranded DNA genome that predominantly has a negative polarity. In recent years, they have received particular attention due to their potential role in the biological control of pathogenic arboviruses and to their unnoticed presence in cell cultures as contaminants. In addition, brevidensoviruses may also be useful as viral vectors. This study describes the first genetic and biological characterization of a mosquito densovirus that was isolated in Brazil; moreover, we examined the phylogenetic relationship between this isolate and the other brevidensoviruses. We further demonstrate that this densovirus has the potential to be used to biologically control dengue virus (DENV) infection with in vitro co-infection experiments. The present study provides evidence that this densovirus isolate is a fast-spreading virus that affects cell growth and DENV infection.

Expression,Purification,Preparation of Polyclonal Antibody and Subcelluar Localization of the NS2 Protein of Periplaneta fuliginosa Densovirus / 微生物学通报

NS2 is a nonstructural protein of Periplaneta fuliginosa densovirus(PfDNV) with a molecular mass of 30 kD,whose function is not yet clearly understood. In order to study the expression,subcellular distribution and the function of NS2 protein,the coding region of NS2 was amplified from the hindgut tissue of cockroaches infected with PfDNV by RT-PCR and then the recombinant prokaryotic expression vector pET28a-NS2 was constructed. The recombinant plasmid was transformed into E. coli BL21(DE3) to express the 6?His fusion protein in the bacteria. After purification,the fusion protein was injected into New Zealand rabbits to prepare polyclonal antibody. The specificity of the anti-NS2 antibody was successfullyproved by western blotting on the eukaryotic expressed products of NS2 protein.Meanwhile,the full sequence of ns2 gene was also cloned into the eukaryotic expression vector pAC. The recombinant plasmid pAC-NS2 was then transfected into Schneider line 2(S2) cells to express NS2 protein in the insect cells. The subcellular localization of NS2 in the insect cells was then investigated by indirect immunofluorescence technique using the anti-NS2 polyclonal antiserum. The confocal laser scanning microscope observation showed that NS2 protein was located primarily in the cytoplasm with some punctate nuclear staining.

Pathogenicity of diatraea saccharalis Densovirus to Host Insets and Characterization of its Viral Genome / 中国病毒学

Pathogenicity of the Diatraea saccharalis densovirus (DsDNV) was tested on its host larvae.The results showed that up to 4 days after inoculation,no larvae mortality was observed and the infected larvae started to exhibit the infection symptoms from the fourth day.After 5 days of infection,the cumulative mortality of infected larvae increased significantly and reached 60% after 12 days and 100% after 21 days of infection,whereas that of the control group was only 10% and 20%,respectively,after same periods of infection,suggesting that the high mortality of infected larvae groups was due to the high pathogenicity of DsDNV.The size of the DsDNA was determined by Electron microscopy visualization of viral DNA molecules and gel electrophoresis of both native and endonuclease digested DNA fragments.The total length of the native DsDNA was about 5.95 kb.The DsDNV DNA was digested with 16 restriction enzymes and a restriction map of those enzymes was constructed with 41 restriction sites.Comparison of the restriction map of the DsDNV genome with those of the genomes ofJunonia coenia densovirus (JcDNV) and Galleria mellonella densovirus (GmDNV) indicated that the three densovirus genomes were found to share many identical restriction sites.Thus,most of the restriction sites of the following endonucleases Bam H Ⅰ,Hha Ⅰ,Xba Ⅰ,Cla Ⅰ,Asp 700,Spe Ⅰ,Nco Ⅰ and Bcl Ⅰ,were found to be conserved among the three densovirus genomes.Symmetrical cleavage sites mapped at the both ends of the genome suggested the presence of inverted terminal repeats (ITRs) whose size was estimated to be about 500 bp.The similar genome size,almost identical restriction sites and presence of an ITR of about 500 bp for these three densoviruses suggested that they belong to the same group of ambisense densoviruses.