Abstract
BackgroundJapanese encephalitis (JE) is a mosquito-borne infectious disease caused by Japanese encephalitis virus (JEV). About 1–10 cases with severe central nervous system symptoms have been constantly reported every year in Japan. To clarify the mechanism of maintenance of JEV, the present study surveyed pigs for serological evidence of JEV infection and isolated JEV strains from pigs and mosquitoes in Isahaya City (Isahaya) and Goto City (Goto) in the islets of Goto in Nagasaki Prefecture from 2008 to 2014.ResultsThe serological survey of pigs showed the increase of IgM sero-positivity against JEV in July or August, and it was maintained until October or November in both Isahaya and Goto every year. There were 47 JEV strains isolated in Nagasaki from 2001 to 2014 including the isolates in this study, and they belonged to genotype 1. Thirty four of the isolated strains were from pigs in Isahaya and were classified under six subclusters (1-A-1, 1-A-2, 1-A-3, 1-A-4, 1-A-5, and 1-A-9). Thirteen strains were isolated from pigs and mosquitoes in Goto and were classified into three subclusters (1-A-5 (2008); 1-A-1 (2009); and 1-A-2). In the subcluster 1-A-2, three different monophyletic subgroups, 1-A-2-2 (2010), 1-A-2-3 (2011), and 1-A-2-1 (2013, 2014), appeared in Goto.ConclusionsThese data strongly suggested that JEV appearance in Goto seems to depend on the frequent introduction of JEV from outside of the island and this pattern is different from what has been observed in subtropical islands in the East China Sea such as Okinawa and Taiwan, where the same populations of JEV (1-A-7 (1998–2008) in Okinawa; genotype 3 (until 2012) in Taiwan) have been maintained for a long period.
Highlights
Japanese encephalitis (JE) is a mosquito-borne infectious disease caused by Japanese encephalitis virus (JEV)
In Japan, JE has decreased drastically due to the introduction of JEV vaccination since the 1970s; still around 1–10 JE patients with central nervous system (CNS) symptoms are constantly reported every year in the western part of Japan including Nagasaki Prefecture
Sequencing To complete the nucleotide sequence of the envelope (E) gene of each of the 47 JEV strains isolated in Nagasaki (Table 1), amplified PCR products were purified using QIAquick Gel Extraction Kit (Qiagen, Hilden, Germany) according to the manufacturer’s instructions
Summary
Japanese encephalitis (JE) is a mosquito-borne infectious disease caused by Japanese encephalitis virus (JEV). About 1–10 cases with severe central nervous system symptoms have been constantly reported every year in Japan. Japanese encephalitis virus (JEV) belongs to the family Flaviviridae, genus Flavivirus. It has a positive-sense single-stranded RNA genome which consists of approximately 11,000 nucleotides. Japanese encephalitis (JE) is caused by JEV infection through a mosquito bite. Most cases are asymptomatic; one out of 100 to 1000 case patients develops clinical symptoms such as high fever, headache, and vomiting, and some are severe central nervous system (CNS) symptoms such as convulsion, paralysis, coma, and Yoshikawa et al Tropical Medicine and Health (2016) 44:8 encephalitis, which eventually lead to a fatal outcome. In Japan, JE has decreased drastically due to the introduction of JEV vaccination since the 1970s; still around 1–10 JE patients with CNS symptoms are constantly reported every year in the western part of Japan including Nagasaki Prefecture
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