Molecular epidemiology of Japanese encephalitis virus in mosquitoes during an outbreak in China, 2013

Abstract

Japanese encephalitis virus (JEV) can cause serious encephalitis and Culex mosquitoes are the primary vector. In 2013, a JE outbreak occurred in Shandong Province, China with 407 confirmed cases, including 11 deaths. An investigation on JEV in mosquitoes during the outbreak was conducted. A total of 14,719 mosquitoes were collected at 3 sites. For the 12,695 Culex tritaeniorhynchus mosquitoes, 88/201 pooled samples were positive by RT-PCR for the presence of the pre-membrane or envelope protein coding genes. The maximum likelihood estimates of JEV positive individuals per 1,000 vectors were 12.0, 7.2, and 6.0 in the 3 sites respectively with an overall estimate of 9.1. Phylogenetic analysis on these pre-membrane (n = 72) and envelope (n = 26) sequences with those of reference strains revealed they belonged to genotype I. This study describes the molecular epidemiology of JEV and suggests the high infection rate in mosquitoes is an important factor for the outbreak.

Figure 1. Clinical cases of Japanese encephalitis in Shandong Province, China, 2005–2013.

Figure 2. Collection sites of mosquitoes in Shandong Province, China in 2013.

Maps were created using Mapinfo software; data are from the National Fundamental Geographic Information System (NFGIS) website (http://ngcc.sbsm.gov.cn/).

Figure 3. Phylogenetic tree on 650-nt PrM gene of JEV strains.

Shandong strains from mosquitoes in 2013 all belong to genotype I. Branch names in red, green, and blue indicate strains from Kenli, Rongcheng, and Junan, respectively. Triangles indicate strains from mosquitoes in Shandong in 2010.

Figure 4. Phylogenetic tree on 1500-nt envelope gene of JEV strains.

Shandong strains in 2013 all belong to genotype I. Branch names in red, green, and blue indicate strains from Kenli, Rongcheng, and Junan, respectively. Triangles indicate strains from mosquitoes in Shandong in 2010.

Figure 5. Comparison of amino acids differences in the envelope protein between the Japanese encephalitis vaccine strains that have been used in China and those identified in mosquitoes for this study.

P3 and SA-14-14-2 are sequences from vaccine strains. Only 5 sequences from mosquitoes are displayed because amino acid sequence comparison on E protein showed that 19 strains had 100% identical aa sequence (strain KL59 represented), 4 strains had identical sequences (strain KL68 represented), and the sequences of the rest 3 strains (strains KL86, KL70 and RC47) are not identical with any of the others.