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1 State Key Laboratory for Infectious Disease Prevention and Control, Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, 100 YingXinJie, XuanWuQu, Beijing 100052, People's Republic of China
2 Department of Virology 1, National Institute of Infectious Diseases, 1-23-1 Toyama, Shinjuku-ku, Tokyo 162-8640, Japan
3 Department of Arbovirus and Chlamydia, Yunnan Institute of Endemic Diseases Control and Prevention, 33 Wenhua Rd, Dali City 67100, Yunnan Province, People's Republic of China
4 Department of Virology, Guizhou Province Center for Disease Control and Prevention, 73 BaGeYanLu, GuiYang City 550004, Guizhou Province, People's Republic of China
5 Department of Virology, Henan Province Center for Disease Control and Prevention, 47 WeiWuLu, Zhengzhou City 450003, Henan Province, People's Republic of China
6 Department of Virology, Sichuan Province Center for Disease Control and Prevention, 40 HuaiShuJie, Chendu City 610031, SiChuan Province, People's Republic of China
7 Chinese Center for Disease Control and Prevention, 29 NanWeiLu, XuanWuQu, Beijing 100050, People's Republic of China
Correspondence
Guo Dong Liang
gdliang{at}hotmail.com
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTS AND DISCUSSIONREFERENCES |
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTS AND DISCUSSIONREFERENCES |
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; Vaughn & Hoke, 1992). Japanese encephalitis (JE) is the most important cause of epidemic viral encephalitis in the South-East Asian and western Pacific regions, the Indian subcontinent and China, with an estimated 35 000–50 000 reported cases and 10 000 deaths annually. Of JE cases, around 25 % are fatal, and nearly 50 % of survivors, especially young children, display persistent neurological and/or psychological sequelae (Burke & Leake, 1988). JEV exists in a zoonotic cycle between mosquitoes and pigs and/or water birds (Monath & Heinz, 1996). Since the first report in 1949, JE epidemics have occurred in China for over 50 years. JEV is active in all of the provinces in China except for Tibet, Xinjiang and Qinghai provinces, and nearly 80 % of globally reported cases occur in China. In China, the most important vector is Culex tritaeniorhynchus.
Phylogenetic analyses of JEV first focused on the prM region with limited sequence information (Chen et al., 1990, 1992; Huong et al., 1993; Ali & Igarashi, 1997), and JEV strains were divided into four genotypes. Then, the E region was targeted for JEV phylogenetic analyses and JEV strains were divided into five genotypes, with one isolate from Singapore (Ni & Barrett, 1995; Paranjpe & Banerjee, 1996; Mangada & Takegami, 1999; Williams et al., 2000; Solomon et al. 2003; Nga et al. 2004). Molecular biological research of JEV strains isolated in China is important for understanding the characteristics of JEV circulating in Asia. So far, there has been only limited information about the genetic difference among JEV strains isolated throughout China. It was reported that JEV isolated between 1949 and 1987 belonged to genotype 3 (Li et al., 2004). It was reported recently that JEV strains isolated in Shanghai in 2001 belonged to genotype 1 (Wang et al., 2004) and that those isolated in Fujian Province in 2002 belonged to genotype 3 (Chen et al., 2005).
In the present study, JEV strains isolated in different areas of China during the period 1949–2005 were analysed and compared with a large group of previously published JEV strains, especially those from China. The study will provide information necessary for understanding JEV molecular epidemiology in Asia.
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METHODS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTS AND DISCUSSIONREFERENCES |
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. Among them, 56 virus isolates were obtained by inoculation onto C6/36 cells and six by inoculation into mouse brains. One isolate from 1979 and seven isolates from the 1980s from Yunnan Province were newly identified by RT-PCR and included in the analysis (Table 1).
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). The bootstrap probabilities of each node were calculated using 1000 replicates. A bootstrap value of >70 % was defined as the criterion for phylogenetic grouping (Hillis & Bull, 1993). All of the phylogenetic trees were drawn by using TreeView software (Page, 1996). A list of the JEV isolates used for analyses is shown with origin and years of isolation in Tables 1 and 2
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTS AND DISCUSSIONREFERENCES |
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). The JEV isolates from 2001–2005 in China were divided into two genotypes, genotype 1 and genotype 3. Thirty-six isolates in Shanghai (2001, 2003, 2005), Liaoning (2002), Henan (2004) and Sichuan (2004) provinces were clustered in genotype 1, along with those isolated in China during 1979–1986 and two isolates from Japan in 1994 and 2002. Forty-eight isolates in Heilongjiang (2002), Fujian (2002, 2003), Yunnan (2003, 2004) and Guizhou (2004) provinces and Shanghai (2004) were clustered in genotype 3. Sixteen isolates from 1949–1971 and one in 1987 from China were grouped into the other cluster in genotype 3, along with those isolated in neighbouring countries from the 1930s to the 1980s.
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). The JEV isolates from 2001–2005 in China were divided into two genotypes, genotype 1 and genotype 3. Thirty-six isolates in Shanghai (2001, 2003, 2005), Liaoning (2002), Henan (2004) and Sichuan (2004) provinces were clustered in genotype 1, along with those isolated in China during 1979–1986 and those isolated in neighbouring countries, Japan, Korea, Vietnam and Thailand, in the 1990s and 2000s. Forty-eight isolates in Heilongjiang (2002), Fujian (2002, 2003), Yunnan (2003, 2004) and Guizhou (2004) provinces and Shanghai (2004) were clustered in genotype 3. The isolates from China from the 1940s to the 1980s were grouped into the other cluster within genotype 3, along with those isolated in other Asian countries from the 1950s to the 1980s.
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Phylogenetic analyses of the JEV isolates in different geographical areas of the world for long periods of time were done in several studies. Early analyses were based on short, limited sequence of the prM gene (Chen et al., 1990, 1992; Ni & Barrett, 1995; Nam et al., 1996; Paranjpe & Banerjee, 1996; Ali & Igarashi, 1997; Tsuchie et al., 1997; Wu et al., 1998; Mangada & Takegami, 1999). However, it is possible that analysis based on short sequences leads to somewhat unclear and unreliable results (Westaway & Blok, 1997; Kuno et al., 1998). The E gene has mainly been used recently (Ni & Barrett, 1995; Paranjpe & Banerjee, 1996; Mangada & Takegami, 1999; Williams et al., 2000; Solomon et al. 2003; Nga et al. 2004).
There have been limited reports on the molecular epidemiology of JEV in China. Some studies analysed only a few Chinese JEV strains, such as Beijing-1, P3 and SA14 (including the vaccine strains, SA14-2-8 and SA14-14-2), and these strains were isolated before 1960 and belonged to genotype 3. Li et al. (2004) recently reported a phylogenetic analysis of 19 JEV isolates from seven provinces in China, covering a time span of 38 years (1949–1987). In this study, the Chinese isolates were examined in the prM region and they were related closely to the Nakayama strain, which was isolated in Japan and belonged to genotype 3. Wang et al. (2004) isolated seven JEV strains in Shanghai and analysed these isolates. They belonged to genotype 1, and this was the first report of genotype 1 in China. Chen et al. (2005) reported JEV isolates in Fujian Province that were obtained from human blood and belonged to genotype 3. Nevertheless, these analyses were based on the prM gene and only limited numbers of isolates were included. Thus, entire features of JEV strains in China were not presented. In the present study, we obtained a total of 62 isolates from mosquitoes, biting midges, human cerebrospinal fluid and blood samples from 2002–2005. We also included seven JEV isolates from 2001 and 28 isolates from 1949–1986 in China, and 37 strains that were isolated in other countries and represent five JEV genotypes were included in the analyses. We sequenced both the prM and E genes. For comparison with E gene phylogeny, the prM gene sequence was also sequenced and analysed. The prM phylogenetic tree was similar to those from previous reports (Chen et al., 1990, 1992; Huong et al., 1993; Ali & Igarashi, 1997) and also to those from studies in China (Li et al., 2004; Wang et al., 2004; Chen et al., 2005). The new isolates represented eight provinces in China: from Heilongjiang Province in the north to Yunnan Province in the south (Fig. 1). The analyses included the first JE isolate in China (Beijing-1), as well as the new isolate from 2005 (SH05-24). Before the 1980s, genotype 3 JEV was predominant in China, but genotype 1 JEV was detected after 1979 and became predominant in some areas, including Shanghai.
Solomon et al. (2003) suggested that JEV genotype 1 was transported from the South-East Asian region, especially Indonesia and Malaysia, to the north. Factors may include water-bird migration, new irrigation projects and enhancing animal husbandry, mosquito dispersal, natural conditions such as south-to-north wind or typhoon, and transport by ships and aeroplanes (Chen et al., 1992; Ming et al., 1993; Tsuchie et al., 1997; Williams et al., 2000; Nga et al., 2004). It is possible that the intermediate hosts, birds infected with genotype 1 JEV, migrated and spread this genotype of JEV in the western Pacific regions. The introduction of JEV belonging to genotype 1 was reported recently in Japan (Takegami et al., 2000), Vietnam (Nga et al., 2004), Korea (Nam et al., 2001) and China (Wang et al., 2004). The first JEV strain belonging to genotype 1 in this region was reported in 1994 (Takegami et al., 2000). All previous isolates in these countries belonged to genotype 3.
Previous studies reported two distribution patterns of JEV. In the northern temperate regions, JEV strains belonged to genotype 1 and genotype 3, and were active and epidemic. Near equatorial areas, genotypes 2 and 4 were active and endemic (Burke & Leake, 1988; Chen et al., 1992; Huong et al., 1993). JE has been a continuously epidemic disease in China since 1949 and the number of JE patients has increased from July to September each year. Recently, there appeared to be two genotypes of JEV in some areas, but not all the provinces. In Heilongjiang, Beijing, Shaanxi, Guizhou and Fujian provinces, we found only genotype 3. The genotype distribution of JEV isolates seems to be changing in various regions. However, there is also a possibility that both genotypes of JEV are active simultaneously in Yunnan and Shanghai.
The results in the present study indicate that: (i) recent JEV isolates in China are divided into two genotypes, genotype 1 and genotype 3; (ii) recent JEV isolates in China are grouped in the same clusters within genotypes 1 and 3; and (iii) genotype 1 JEV strains have been isolated in China since 1979, whilst genotype 3 JEV strains have been isolated since the 1940s. These results suggest that genotype 1 JEV was introduced to China in recent years and that JEV belonging to genotypes 1 and 3 co-circulates. We will continue to isolate new JEV strains, especially from human beings. The study will provide a deep insight into the complex molecular epidemiology of JEV in east Asia, including China.
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ACKNOWLEDGEMENTS |
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTS AND DISCUSSIONREFERENCES |
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Received 8 May 2006;
accepted 29 October 2006.
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