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Additional file 1: Figure S1. GDP per capita of counties in Guizhou Province. Figure S2. The climate variability including cumulative precipitation, average temperature. Figure S3. The land use of urban area, cropland, water body and vegetation coverage of counties in Guizhou Province.

The proportion of laboratory-confirmed Japanese encephalitis (JE) virus (JEV) infections was compared to the number of JE cases reported on the basis of seasonality and the clinical symptoms of hospitalized patients in Guizhou Province, China, between April and November 2006. Of the 1,837 patients with reported JE, 1,382 patients in nine prefectures were investigated. JE was confirmed in 1,210 of 1,382 (87.6%) patients by a JEV-specific immunoglobulin M (IgM) antibody-capture enzyme-linked immunosorbent assay (MAC-ELISA), heminested reverse transcriptase PCR, and virus isolation. Two strains of JEV belonging to genotype 1 were isolated. Other viral pathogens responsible for encephalitis, including echovirus, mumps virus, herpes simplex virus, and cytomegalovirus, were identified in 67 of 172 (38.9%) JE-negative cases. On the basis of the distribution of the laboratory-confirmed JE cases from different hospitals according to the Chinese administrative division, which included hospitals at the provincial, city, county, and township levels, county hospitals detected the highest number of JE cases (81.8%), whereas township hospitals detected the smallest number of JE cases (1.4%). Provincial and city hospitals had the highest and lowest rates of accuracy of providing a clinical diagnosis of JE, as confirmed by laboratory testing (91.8% and 76.7%, respectively). This study demonstrates that laboratory confirmation improves the accuracy of diagnosis of JE and that an enhanced laboratory capacity is critical for JE surveillance as well as the identification of other pathogens that cause encephalitic syndromes with clinical symptoms similar to those caused by JEV infection.

Background Culexflavivirus (CxFV) is an insect specific virus that has been isolated from Culexpipiens, Culexquinquefasciatus, Culextritaeniorhynchus and other Culex mosquitoes. It is a novel flavivirus isolated in Asia, North America, Central America and Africa. Phylogenetic analysis indicates that, based on the envelope gene (E gene) sequence, the worldwide CxFV strains can be divided into two genotypes. Result A virus (SDDM06-11) was isolated from Culexpipiens collected in Shandong Province, China in 2006. The strain caused cytopathic effect (CPE) in Aedesalbopictus (C6/36) cells by 3 days post-infection and immunofluorescence assay (IFA) showed a reaction with Japanese encephalitis virus (JEV) polyclonal antibodies. Phylogenetic analysis of the E gene sequence showed CxFV formed two genotypes with the SDDM06-11 strain assigned to genotype 1. Analysis of the E gene nucleotide homology showed the virus possessed characteristic amino acids at specific sites. The nucleotide homology of the open reading frame (ORF) was 94.8%-95.1% between SDDM06-11 and isolates from Japan, Iowa and Texas, and 90.2%-90.5% between SDDM06-11 and isolates from Uganda and Mexico. Conclusion In this paper we report the first isolation and identification of an isolate of CxFV in mainland China. Phylogenetic analysis indicates the isolate belongs to genotype 1. Our findings provide insight into the occurrence of CxFV in Culex mosquito populations and its distribution on a global scale.