Distribution And Identification Of Mosquitoes And Mosquito-borne Arbovirus In Shandong Province China

BackgroundArboviruses are a class of viruses that can spread diseases by blood-sucking arthropod bites vertebrates, including mosquitoes, ticks, sand flies, midges and mites. Arbovirus reproduced in arthropods, but not a pathogenic to arthropod, after a certain incubation period, the virus was transmitted to a new vertebrate host through biting. Arbovirus was distributed in global area, but mainly located in temperate, subtropical and tropical regions. Most arboviruses have geographical distribution. The international community has discovered 537 species of arbovirus, which can cause more than 130 human and animal diseases. Arbovirus diseases have become the focus of attention of the international community public health problem. Arbovirus diseases have become the public health issue that cause attention of international community. Shandong province is located in eastern coast of China, and in the lower of Yellow River. The climate of Shandong Province is warm temperate humid and semi-humid monsoon. The population is density, the geographical condition is complexity, and the climate is warm and humid. These entire situations are suitable for breeding arbovirus and forming a diversity species of insect vectors. However, so far only JE (Japanese Encephalitis, JE) cases reported in Shandong Province. Most unexplained fever and encephalitis cases are exist. It needs to understand the relationship between the mosquito-borne virus and the local disease. The results can provide biasis prevention and control for local arbovirus diseases. ObjectiveThrough a systematic survey of arboviruses in Shandong province to provide biasis for prevention and control for local arbovirus disease and it can also provide diagnoses information for unknown fever cases in summer and autumn in Shandong.MethodsMosquito-grinding supernatant was inoculated into C6/36 cells and BHK-21 cells. The positive isolates were identified using serological and molecular biology techniques; The specific gene segment was amplificated and sequenced directly, amino acid sequence analysis and phylogenetic analysis were carried out by using ClustalX1.83, MegAlign, Mega4 and Genedoc3.2 software. Meanwhile the cDNA library was prepared and the nucleic acid of JEV detected, then the infection rate of JEV in mosquito samples calculated.Results1. We choose 7 collection sites in Shandong province to collect mosquito samples.They are Yantai, Qingdao and Dongying in east area; Zibo and Jinan in middle area; Jining and Heze in southwest area. Totally 19 211 mosquitoes divided into 322 pools were collected in 7 collection sites. The mosquito samples include 5 genera and 6 species, including Cx.tritaeniorhynchus,Culex.pipienspallens, An.sinensis, Ar.subalbatus, Mansonia uniformis and Aede. The dominant species in Yantai, Qingdao and Zibo is the Culex pipienspallens. The dominant species in Jinan, Dongying, Heze and Jining is the Culex tritaeniorhynchus, the mosquito collected in Yantai in 2009 is most variety, and it has all mosquito species except Mansonia uniformis. The Mansonia uniformis species was collected only in Jining.2. Through the tissue culture method, totally 33 positive isolates were obtained in Shandong province in 2008 and 2009.21 isolates were identified for JEV,1 is GETV,1 is BAV, another 10 are CppDNV. Molecular analysis of JEV showed that 21 JEV isolates were all clustered into genotype I and showed the clear geographical features.21 strains of JEV showed a high homology which between 97.3%～100%, and the nucleotide homology with vaccine strains SA14-14-2 E gene is 87.2%～88.1%; The nucleotide homology with isolates from Shanghai, Henan and Vietnam is 97.6%-99.4%. There are 11 common amino acid different from JE live attenuated vaccine SA14-14-2 in E gene, but the position which can decide the antigenicity and the virulence are not changing.The full-length 3'UTR of the GETV is 401nt, it is similar with other strains in China, Mongolia and Russian existing lOnt missing in 45～54nt. Based on the 12th segment of BAV indicate the newly isolates has the highest homology with LN0688 and LN0689. Phylogenetic display, SDWS0909 belongs to A2 sub-groups which are in northern group of China.10 CppDNV based on NS1 gene sequence analysis indicates the homology with CppDNV (JZ-16; YN05217; EF579757; EF579771; YN05169, EF579770; XJ0545; GZWN1) are higher than 99%.3. To understand the JEV infection rate in mosquitoes, we detected the nucleotide of JEV in mosquito samples we collected. The total infection rate is 21.5%(52/242) The infection rate in 2008 and 2009 are respectively 36.6%(34/93) and 12.1%(18/149). The results indicate that high risk infection exist in nature environment in shandong province. We detected JEV nucleotide from Cx.tritaeniorhynchus, Cx.pipienspallens, An.sinensis and Aede. The results indicate that many mosquito species in Shandong province can transmission the JEV. We should pay more attention to this situation. We also do the analysis for the ditrbution of JE cases in Shandong province.ConclusionThis is the first systematic and comprehensive investigation of mosquito and mosquito-borne arbovirus in Shandong Province. Totally 19211 mosquitoes belong to 5 genera and 6 species were collected. Culex were the dominant species in local area. JEV, GETV, BAV and CppDNV were isolated from 3 spieces mosquito samples. This result suggest that there is high infectious risk in Shandong province.