Molecular epidemiological analyses of Japanese encephalitis virus isolates from swine in Japan from 2002 to 2004

Antiviral Efficacy of RNase H-Dependent Gapmer Antisense Oligonucleotides against Japanese Encephalitis Virus

RNase H-dependent gapmer antisense oligonucleotides (ASOs) are a promising therapeutic approach via sequence-specific binding to and degrading target RNAs. However, the efficacy and mechanism of antiviral gapmer ASOs have remained unclear. Here, we investigated the inhibitory effects of gapmer ASOs containing locked nucleic acids (LNA gapmers) on proliferating a mosquito-borne flavivirus, Japanese encephalitis virus (JEV), with high mortality. We designed several LNA gapmers targeting the 3' untranslated region of JEV genomic RNAs. In vitro screening by plaque assay using Vero cells revealed that LNA gapmers targeting a stem-loop region effectively inhibit JEV proliferation. Cell-based and RNA cleavage assays using mismatched LNA gapmers exhibited an underlying mechanism where the inhibition of viral production results from JEV RNA degradation by LNA gapmers in a sequence- and modification-dependent manner. Encouragingly, LNA gapmers potently inhibited the proliferation of five JEV strains of predominant genotypes I and III in human neuroblastoma cells without apparent cytotoxicity. Database searching showed a low possibility of off-target binding of our LNA gapmers to human RNAs. The target viral RNA sequence conservation observed here highlighted their broad-spectrum antiviral potential against different JEV genotypes/strains. This work will facilitate the development of an antiviral LNA gapmer therapy for JEV and other flavivirus infections.

Growth, Pathogenesis, and Serological Characteristics of the Japanese Encephalitis Virus Genotype IV Recent Strain 19CxBa-83-Cv

Genotype IV Japanese encephalitis (JE) virus (GIV JEV) is the least common and most neglected genotype in JEV. We evaluated the growth and pathogenic potential of the GIV strain 19CxBa-83-Cv, which was isolated from a mosquito pool in Bali, Indonesia, in 2019, and serological analyses were also conducted. The growth ability of 19CxBa-83-Cv in Vero cells was intermediate between that of the genotype I (GI) strain Mie/41/2002 and the genotype V (GV) strain Muar, whereas 19CxBa-83-Cv and Mie/41/2002 grew faster than Muar in mouse neuroblastoma cells. The neuroinvasiveness of 19CxBa-83-Cv in mice was higher than that of Mie/41/2002 but lower than that of Muar; however, there were no significant differences in neurovirulence in mice among the three strains. The neutralizing titers of sera from 19CxBa-83-Cv- and Mie/41/2002-inoculated mice against 19CxBa-83-Cv and Mie/41/2002 were similar, whereas the titers against Muar were lower than those of the other two viruses. The neutralizing titers of JE vaccine-inoculated mouse pool serum against 19CxBa-83-Cv and Muar were significantly lower than those against Mie/41/2002. The neutralizing titers against the three viruses were similar in three out of the five serum samples from GI-infected JE patients, although the titers against Mie/41/2002 were higher than those against 19CxBa-83-Cv and Muar in the remaining two sera samples. In summary, we identified the basic characteristics of 19CxBa-83-Cv, but further studies are needed to better understand GIV JEV.

Epidemiological investigation of swine Japanese encephalitis virus based on RT-RAA detection method

JEV is one of the zoonotic pathogens that cause serious diseases in humans. JEV infection can cause abortion, mummified foetus and stillbirth in sows, orchitis and semen quality decline in boars, causing huge economic losses to pig industry. In order to investigate the epidemiology of JEV in pigs in Sichuan province, a rapid and efficient fluorescent Reverse transcription recombinase-aided amplification (RT-RAA) detection method was established. Aborted fetuses and testicular swollen boar samples were detected by RT-RAA in pigs in the mountain areas around Sichuan Basin, and the detection rate of JEV was 6.49%. The positive samples were identified as JEV GI strain and GIIIstrain by sequencing analysis. We analyzed the whole gene sequence of a positive sample for the GI virus. The Envelope Protein (E protein) phylogenetic tree analysis was far related to the Chinese vaccine strain SA14-14-2, and was most closely related to the JEV GI strains SH17M-07 and SD0810 isolated from China. The results showed that we established an efficient, accurate and sensitive method for clinical detection of JEV, and JEV GI strains were prevalent in Sichuan area. It provides reference for the prevention and control of JEV in Sichuan.

Re-Examining the Importance of Pigs in the Transmission of Japanese Encephalitis Virus

Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, is the leading cause of pediatric encephalitis in Southeast Asia. The enzootic transmission of JEV involves two types of amplifying hosts, swine and avian species. The involvement of pigs in the transmission cycle makes JEV a unique pathogen because human Japanese encephalitis cases are frequently linked to the epizootic spillover from pigs, which can not only develop viremia to sustain transmission but also signs of neurotropic and reproductive disease. The existing knowledge of the epidemiology of JEV largely suggests that viremic pigs are a source of infectious viruses for competent mosquito species, especially Culex tritaeniorhynchus in the endemic regions. However, several recently published studies that applied molecular detection techniques to the characterization of JEV pathogenesis in pigs described the shedding of JEV through multiple routes and persistent infection, both of which have not been reported in the past. These findings warrant a re-examination of the role that pigs are playing in the transmission and maintenance of JEV. In this review, we summarize discoveries on the shedding of JEV during the course of infection and analyze the available published evidence to discuss the possible role of the vector-free JEV transmission route among pigs in viral maintenance.

Immunogenicity and Protective Ability of Genotype I-Based Recombinant Japanese Encephalitis Virus (JEV) with Attenuation Mutations in E Protein against Genotype V JEV

Genotype V (GV) Japanese encephalitis virus (JEV) has emerged in Korea and China since 2009. Recent findings suggest that current Japanese encephalitis (JE) vaccines may reduce the ability to induce neutralizing antibodies against GV JEV compared to other genotypes. This study sought to produce a novel live attenuated JE vaccine with a high efficacy against GV JEV. Genotype I (GI)-GV intertypic recombinant strain rJEV-E^XZ0934-M41 (E^XZ0934), in which the E region of the GI Mie/41/2002 strain was replaced with that of GV strain XZ0934, was introduced with the same 10 attenuation substitutions in the E region found in the live attenuated JE vaccine strain SA 14-14-2 to produce a novel mutant virus rJEV-E^XZ/SA14142m-M41 (E^XZ/SA14142m). In addition, another mutant rJEV-E^M41/SA14142m-M41 (E^M41/SA14142m), which has the same substitutions in the Mie/41/2002, was also produced. The neuroinvasiveness and neurovirulence of the two mutant viruses were significantly reduced in mice. The mutant viruses induced neutralizing antibodies against GV JEV in mice. The growth of E^XZ/SA14142m was lower than that of E^M41/SA14142m. In mouse challenge tests, a single inoculation with a high dose of the mutants blocked lethal GV JEV infections; however, the protective efficacy of E^XZ/SA14142m was weaker than that of E^M41/SA14142m in low-dose inoculations. The lower protection potency of E^XZ/SA14142m may be ascribed to the reduced growth ability caused by the attenuation mutations.

Amino Acid at Position 166 of NS2A in Japanese Encephalitis Virus (JEV) is Associated with In Vitro Growth Characteristics of JEV

We previously showed that the growth ability of the Japanese encephalitis virus (JEV) genotype V (GV) strain Muar is clearly lower than that of the genotype I (GI) JEV strain Mie/41/2002 in murine neuroblastoma cells. Here, we sought to identify the region in GV JEV that is involved in its low growth potential in cultured cells. An intertypic virus containing the NS1-3 region of Muar in the Mie/41/2002 backbone (NS1-3^Muar) exhibited a markedly diminished growth ability in murine neuroblastoma cells. Moreover, the growth rate of a Muar NS2A-bearing intertypic virus (NS2A^Muar) was also similar to that of Muar in these cells, indicating that NS2A of Muar is one of the regions responsible for the Muar-specific growth ability in murine neuroblastoma cells. Sequencing analysis of murine neuroblastoma Neuro-2a cell-adapted NS1-3^Muar virus clones revealed that His-to-Tyr mutation at position 166 of NS2A (NS2A¹⁶⁶) could rescue the low replication ability of NS1-3^Muar in Neuro-2a cells. Notably, a virus harboring a Tyr-to-His substitution at NS2A¹⁶⁶ (NS2A^Y166H) showed a decreased growth ability relative to that of the parental virus Mie/41/2002, whereas an NS2A^Muar-based mutant virus, NS2A^Muar-H166Y, showed a higher growth ability than NS2A^Muar in Neuro-2a cells. Thus, these results indicate that the NS2A¹⁶⁶ amino acid in JEV is critical for the growth and tissue tropism of JEV in vitro.

Role of pattern recognition receptors and interferon-beta in protecting bat cell lines from encephalomyocarditis virus and Japanese encephalitis virus infection

Bats are potential natural hosts of Encephalomyocarditis virus (EMCV) and Japanese encephalitis virus (JEV). Bats appear to have some unique features in their innate immune system that inhibit viral replication causing limited clinical symptoms, and thus, contributing to the virus spill over to humans. Here, kidney epithelial cell lines derived from four bat species (Pteropus dasymallus, Rousettus leschenaultii, Rhinolophus ferrumequinum, and Miniopterus fuliginosus) and two non-bat species (Homo sapiens and Mesocricetus auratus) were infected with EMCV and JEV. The replication of EMCV and JEV was lower in the bat cell lines derived from R. leschenaultii, R. ferrumequinum, and M. fuliginosus with a higher expression level of pattern recognition receptors (PRRs) (TLR3, RIG-I, and MDA5) and interferon-beta (IFN-β) than that in the non-bat cell lines and a bat cell line derived from P. dasymallus. The knockdown of TLR3, RIG-I, and MDA5 in Rhinolophus bat cell line using antisense RNA oligonucleotide led to decrease IFN-β expression and increased viral replication. These results suggest that TLR3, RIG-I, and MDA5 are important for antiviral response against EMCV and JEV in Rhinolophus bats.

E and prM proteins of genotype V Japanese encephalitis virus are required for its increased virulence in mice

We previously showed that the Japanese encephalitis virus (JEV) genotype V (GV) strain Muar exhibits significantly higher virulence in mice than the genotype I (GI) JEV strain Mie/41/2002. In this study, we attempted to identify the region responsible for the increased virulence of GV JEV using recombinant intertypic and single mutant JEVs. Intertypic viruses containing the GV E region in the Mie/41/2002 backbone showed increased pathogenicity in mice. The amino acid at position 123 in the E protein (E123) of the Mie/41/2002 and GV JEVs was serine and histidine, respectively. A serine-to-histidine substitution at E123 of the Mie/41/2002 increased its virulence. However, histidine-to-serine changes at E123 in the intertypic mutants with the GV E region remained highly virulent. GV Muar prM-bearing mutants were also highly pathogenic in mice. Our results suggest that the E and prM proteins of GV JEV are responsible for the highly virulent characteristics of GV JEV.

Upregulated expression of the antioxidant sestrin 2 identified by transcriptomic analysis of Japanese encephalitis virus-infected SH-SY5Y neuroblastoma cells

Japanese encephalitis virus (JEV) exerts a profound burden of viral encephalitis. We have investigated the differentially expressed transcripts in the neuronal transcriptome during JEV infection by RNA sequencing (RNA-Seq) of virus-infected SH-SY5Y human neuroblastoma cells. Gene ontology analysis revealed significant enrichment from two main pathways: endoplasmic reticulum (ER)-nucleus signaling (P value: 5.75E-18; false discovery rate [FDR] 3.11E-15) and the ER unfolded protein response (P value: 7.58E-18; FDR 3.11E-15). qPCR validation showed significant upregulation and differential expression (P < 0.01) of ER stress-signaling transcripts (SESN2, TRIB3, DDIT3, DDIT4, XBP1, and ATF4) at 24 h post-infection for both low (LN) and high (HN) neurovirulence JEV strains. Immunoblot analysis following JEV infection of SH-SY5Y cells showed an increase in levels of SESN2 protein following JEV infection. Similarly, Zika virus (MR766) infection of SH-SY5Y showed a titer-dependent increase in ER stress-signaling transcripts; however, this was absent or diminished for DDIT4 and ATF4, respectively, suggestive of differences in the induction of stress-response transcripts between flaviviruses. Interestingly, SLC7A11 and SLC3A2 mRNA were also both deregulated in JEV-infected SH-SY5Y cells and encode the two constituent subunits of the plasma membrane xCT amino acid antiporter that relieves oxidative stress by export of glutamate and import of cystine. Infection of SH-SY5Y and HEK293T cells by the JEV HN strain Sw/Mie/40/2004 lead to significant upregulation of the SLC7A11 mRNA to levels comparable to DDIT3. Our findings suggest upregulation of antioxidants including SESN2 and, also, the xCT antiporter occurs to counteract the oxidative stress elicited by JEV infection.

Detection of a novel tick-borne flavivirus and its serological surveillance

Tick-borne encephalitis virus (TBEV), a flavivirus that causes severe neurological symptoms in humans, has been found in Hokkaido, Japan. In the present study, we detected sequences from a novel tick-borne flavivirus, designated Yamaguchi virus (YGV), in liver and serum samples obtained from a wild boar in the Yamaguchi prefecture, Japan. Phylogenetic analysis revealed that YGV belongs to the TBEV complex and is closely related to Langat virus (LGTV). YGV was also detected by specific RT-PCR from 20 in 378 pools of ticks (2923 ticks) collected in Yamaguchi and Wakayama prefectures and from seven in 46 wild boar captured in Wakayama. The major ticks infected with YGV belong to the genus Haemaphysalis. Unfortunately, YGV could not be isolated from any samples from the RT-PCR positive wild boar or ticks. Therefore, ELISA for detection of antibodies against YGV was established using LGTV, and surveillance was performed among wild boar in 10 different prefectures on Honshu Island, the main island of Japan. The results showed that the seroprevalence of tick-borne flavivirus infection in the Wakayama and Hyogo prefectures of western Japan was significantly higher than that in the other prefectures, while antibodies against tick-borne flavivirus were not detected in any wild boar in the Tochigi prefecture in the eastern part of Japan. In addition, wild raccoons or masked palm civets in the Hyogo prefecture did not possess detectable antibodies against tick-borne flaviviruses. In conclusion, YGV appears to be maintained primarily among wild boar and ticks in the western part of Japan. YGV is the second flavivirus (after Japanese encephalitis virus) shown to be circulating on Honshu Island in Japan.

Stearoyl-CoA desaturase-1 is required for flavivirus RNA replication

Dengue virus (DENV) is the most prevalent human arthropod-borne virus and causes severe problems worldwide, mainly in tropical and sub-tropical regions. However, there is no specific antiviral drug against DENV infection. We and others recently reported that stearoyl-CoA desaturase-1 (SCD1) inhibitor showed potent suppression of hepatitis C virus replication. In this study, we examined the impact of SCD1 on DENV replication. We found that SCD1 inhibitors (MK8245 and #1716) dramatically suppressed DENV replication in a dose-dependent manner without cytotoxicity. This anti-DENV efficacy was observed against all four DENV serotypes and other flaviviruses, including Zika virus and Japanese encephalitis virus. A subgenomic replicon system of DENV was used to confirm that SCD1 inhibitor suppressed viral RNA replication. Interestingly, exogenous supplementation of unsaturated fatty acids resulted in recovery of the DENV titer even in the presence of SCD1 inhibitor, suggesting that fatty acid biosynthesis contributes to DENV genome replication. These findings indicate that SCD1 is a novel host factor required for DENV replication, and SCD1 inhibitor is a potential candidate for treating dengue fever.

Detection of anti-viral antibodies from meat juice of wild boars

Wild boars are a reservoir for many zoonotic pathogens and a good sentinel for surveillance of zoonotic viral infections, but collection of serum samples from wild boars in the field is sometimes difficult and requires special equipment and techniques. In this study, ELISA using meat juices extracted from the heart and diaphragm of wild boars, instead of serum samples, was performed to detect antibodies against zoonotic pathogens, Japanese encephalitis virus and hepatitis E virus. The results of ELISA using meat juice samples were significantly correlated with those using serum samples and meat juice contained one-fifth the antibodies of serum samples. As meat juice is easily collected from wild animals in the field without special equipment and techniques, ELISA using meat juice is a simple and superior method for serological survey of zoonosis among wild animals.

Virulence of Japanese Encephalitis Virus Genotypes I and III, Taiwan

The virulence of genotype I (GI) Japanese encephalitis virus (JEV) is under debate. We investigated differences in the virulence of GI and GIII JEV by calculating asymptomatic ratios based on serologic studies during GI- and GIII-JEV endemic periods. The results suggested equal virulence of GI and GIII JEV among humans.

Development of a Japanese encephalitis virus genotype V virus-like particle vaccine in silkworms

To counter the spread of multiple Japanese encephalitis virus (JEV) variants harboured in alternative host species and highly neurotoxic variants with new antigenicity, such as genotype V (Muar), methods for developing more effective and low-cost vaccines against a variety of epidemic JEV strains are required. Here, we successfully synthesized large amounts of a Muar virus-like particle (MVLP) vaccine for JEV in silkworm pupae by using a Bombyx mori nuclear polyhedrosis virus recombinant consisting of JEV codon-optimized envelope (E) DNA. In particular, histopathological examination suggested that MVLP was efficiently synthesized in body fat tissues as well as epithelial cells. Quantitative analysis indicated that one silkworm pupa produced 724.8 µg of E protein in the MVLP vaccine. Electron microscopic examination of purified MVLP vaccine defined a typical MVLP morphological structure. Detailed MVLP antigen assessment by immune-electron microscopy revealed that the majority of MVLPs were covered with approximately 10 nm projections. Boosted immunization with MVLP antigens in mice and rabbits tended to show improved plaque inhibition potency against homologous Muar and heterologous Nakayama, but less potency to Beijing-1 strains. Notably, mixed immune rabbit antisera against Nakayama and Muar VLP antigens led to an increase in the low antibody reaction to Beijing-1. Additionally, a stopgap divalent JEV vaccine consisting of MVLP and Nakayama VLP and its immune mouse serum significantly increased plaque inhibition titre against Muar, Nakayama and Beijing-1 strains. These findings suggested that low-cost MVLP vaccines prepared in silkworm pupae are suitable for providing simultaneous protection of individuals in developing countries against various JEV strains.

Development of a Japanese encephalitis virus-like particle vaccine in silkworms using codon-optimised prM and envelope genes

We have successfully prepared a Japanese encephalitis virus (JEV) - Nakayama virus like particle (NVLP) vaccine using synthetic codon-optimized prM and E genes. The expression of the recombinant JEV Nakayama-BmNPV (JEV-NNPV) virus was determined in infected silkworm Bm-N cells by fluorescence and Western blot analysis. The recombinant was inoculated into silkworm pupae and the yield of Nakayama VLP (NVLP) reached a peak in the homogenates after 3 days. Additionally, in the peptide analysis of infected pupae homogenate, it appeared approximately 300-500 μg E protein/pupa were produced. When purified the above eluates on the discontinuous sucrose density gradient centrifugation, NVLP showed a strong hemagglutination (HA) activity by using chicken red blood cell in phosphate-buffered saline (PBS) free from Mg++ and Ca++ ions. The immune antisera against NVLP strain could efficiently neutralize the plaque formation of Nakayama, Beijing-1 and Muar strains, showing tendency of much higher reaction with heterologous Muar strain than homologous Nakayama strain. Our findings suggest that the JEV-NVLP may be useful for JEV epidemic control in many endemic areas of Asian countries as a widely effective and less expensive JE vaccine.

Insight into SNPs and epitopes of E protein of newly emerged genotype-I isolates of JEV from Midnapur, West Bengal, India

BACKGROUND

Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus that causes Japanese Encephalitis (JE) and Acute Encephalitis Syndrome (AES) in humans. Genotype-I (as co-circulating cases with Genotype-III) was isolated in 2010 (JEV28, JEV21) and then in 2011 (JEV45) from Midnapur district, West Bengal (WB) for the first time from clinical patients who were previously been vaccinated with live attenuated SA14-14-2 strain. We apply bioinformatics and immunoinformatics on sequence and structure of E protein for analysis of crucial substitutions that might cause the genotypic transition, affecting protein-function and altering specificity of epitopes.

RESULTS

Although frequency of substitutions in E glycoprotein of JEV28, JEV21 and JEV45 isolates vary, its homologous patterns remain exactly similar as earlier Japan isolate (Ishikawa). Sequence and 3D model-structure based analyses of E protein show that only four of all substitutions are critical for genotype-I specific effect of which N103K is common among all isolates indicating its role in the transition of genotype-III to genotype-I. Predicted B-cell and T-cell epitopes are seen to harbor these critical substitutions that affect overall conformational stability of the protein. These epitopes were subjected to conservation analyses using a large set of the protein from Asian continent.

CONCLUSIONS

The study identifies crucial substitutions that contribute to the emergence of genotype-I. Predicted epitopes harboring these substitutions may alter specificity which might be the reason of reported failure of vaccine. Conservation analysis of these epitopes would be useful for design of genotype-I specific vaccine.

Molecular and serological epidemiology of Japanese encephalitis virus (JEV) in a remote island of western Japan: an implication of JEV migration over the East China Sea

Background

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. 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.

Results

The 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.

Conclusions

These 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.

Epidemiology of Japanese encephalitis: past, present, and future prospects

Japanese encephalitis (JE) is one of severe viral encephalitis that affects individuals in Asia, western Pacific countries, and northern Australia. Although 67,900 JE cases have been estimated among 24 JE epidemic countries annually, only 10,426 have been reported in 2011. With the establishment of JE surveillance and vaccine use in some countries, the JE incidence rate has decreased; however, serious outbreaks still occur. Understanding JE epidemics and identifying the circulating JE virus genotypes will improve JE prevention and control. This review summarizes the current epidemiology data in these countries.

Establishment and characterization of two new cell lines from the mosquito Armigeres subalbatus (Coquillett) (Diptera: Culicidae)

Armigeres subalbatus (Coquillett) is a medically important mosquito and a model species for immunology research. We successfully established two cell lines from the neonate larvae of A. subalbatus using two different media. To our knowledge, this is the first report of an established Armigeres mosquito cell line. The cell lines, designated as Ar-3 and Ar-13, consist of adherent and diploid cells with compact colonies. Both these cell lines grow slowly after passage at a split ratio of 1:5 and a population doubling time of 2.7 and 3.0 d, respectively. Random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) was used to confirm that these lines correspond to the species of origin and are clearly distinct from seven other insect cell lines. Furthermore, reverse-transcription PCR was used to demonstrate that the Ar-3 cell line is susceptible to the Japanese encephalitis virus and two insect flaviviruses associated with Culex and Aedes mosquitoes but relatively insensitive to dengue virus. These data indicate that the newly established cell lines are cellular models of A. subalbatus as well as beneficial tools for the propagation of viruses associated with the Armigeres mosquito.

Analysis of Mosquito-Borne Flavivirus Superinfection in Culex tritaeniorhynchus (Diptera: Culicidae) Cells Persistently Infected with Culex Flavivirus (Flaviviridae)

Superinfection exclusion is generally defined as a phenomenon in which a pre-existing viral infection prevents a secondary viral infection; this has also been observed in infections with mosquito-borne viruses. In this study, we examined the superinfection exclusion of the vertebrate-infecting flaviviruses, Japanese encephalitis virus (JEV) and dengue virus (DENV), by stable and persistent infection with an insect-specific flavivirus, Culex flavivirus (CxFV), in a Culex tritaeniorhynchus Giles cell line (CTR cells). Our experimental system was designed based on the premise that wild Cx. tritaeniorhynchus mosquitoes naturally infected with CxFV are superinfected with JEV by feeding on JEV-infected animals. As a result, we found no evidence of the superinfection exclusion of both JEV and DENV by pre-existing CxFV infection at the cellular level. However, JEV superinfection induced severe cytopathic effects on persistently CxFV-infected CTR cells. These observations imply the possibility that JEV superinfection in CxFV-infected Cx. tritaeniorhynchus mosquitoes has an adverse effect on their fitness.

Identification and amplification of Japanese encephalitis virus and Getah virus propagated from a single porcine serum sample: a case of coinfection

We detected two viruses, Japanese encephalitis virus (JEV)/Kochi/01/2005 and Getah virus (GETV)/Kochi/01/2005 in the same culture supernatant obtained by inoculation of Vero cells with a swine serum sample and subsequent passaging of the supernatant in Vero cells. Phylogenetic analysis using the nucleotide sequences of the complete genome and the E2 region of GETV indicated that GETV/Kochi/01/2005 is most similar to a Mongolian strain. In contrast, a partial sequence of the nsP1 protein coding region of GETV/Kochi/01/2005 showed that it was similar to Japanese strains isolated in the 1980s. Alignment of the nucleotide sequence of the E region of JEV showed that JEV/Kochi/01/2005 has the highest similarity to a Japanese strain. We also examined the changes in the amount of JEV/Kochi/01/2005 and GETV/Kochi/01/2005 present after passaging in Vero cells. The RNA copy number and infectious titer of JEV/Kochi/01/2005 decreased, whereas those of GETV/Kochi/01/2005 increased, following repeated passages in Vero cells. Our results provide evidence for coinfection with JEV and GETV in the Kochi/01/2005 pig. This is the first report of incidental confection with JEV and GETV in a domestic animal.

Japanese encephalitis in a 114-month-old cow: pathological investigation of the affected cow and genetic characterization of Japanese encephalitis virus isolate

Background

Japanese encephalitis virus (JEV) is classified into the genus Flavivirus in the family Flaviviridae. JEV can cause febrile illness and encephalitis mainly in humans and horses, and occasionally in cattle.

Case presentation

In late September 2010, a 114-month-old cow showed neurological symptoms similar to the symptoms observed in previous bovine cases of Japanese encephalitis (JE); therefore, we conducted virological and pathological tests on the cow. As a result, JEV was isolated from the cerebrum of the affected cow. We determined the complete genome sequence of the JEV isolate, which we named JEV/Bo/Aichi/1/2010, including the envelope (E) gene region and 3’ untranslated region (3’UTR). Our phylogenetic analyses of the E region and complete genome showed that the isolate belongs to JEV genotype 1 (G1). The isolate, JEV/Bo/Aichi/1/2010, was most closely related to several JEV G1 isolates in Toyama Prefecture, Japan in 2007–2009 by the phylogenetic analysis of the E region. In addition, the nucleotide alignment revealed that the deletion in the 3’UTR was the same between JEV/Bo/Aichi/1/2010 and several other JEV G1 isolates identified in Toyama Prefecture in 2008–2009. A hemagglutination inhibition (HI) test was conducted for the detection of anti-JEV antibodies in the affected cow, and the test detected 2-mercaptoethanol (2-ME)-sensitive HI antibodies against JEV in the serum of the affected cow. The histopathological investigation revealed nonsuppurative encephalomyelitis in the affected cow, and the immunohistochemical assay detected JEV antigen in the cerebrum.

Conclusion

We diagnosed the case as JE of a cow based on the findings of nonsuppurative encephalomyelitis observed in the central nervous system, JEV antigen detected in the cerebrum, JEV isolated from the cerebrum, and 2-ME-sensitive HI antibodies against JEV detected in the serum. This is the first reported case of JE in a cow over 24 months old.

Nonsuppurative encephalomyelitis in a calf in Japan and isolation of Japanese encephalitis virus genotype 1 from the affected calf

Japanese encephalitis virus (JEV) was isolated from the cerebrum of a calf which showed severe neurological symptoms in late September 2009, and the JEV isolate was revealed to be of genotype 1. This is the first report describing the isolation of genotype 1 JEV from cattle.

Genomic analysis of a newly isolated of Japanese encephalitis virus strain, CQ11-66, from a pediatric patient in China

BACKGROUND

Japanese encephalitis virus (JEV) is one of the major causative agents of viral encephalitis in East Asia, Southeast Asia and Australia. However, no clinical JEV strain has yet been isolated from JE patients in Chongqing, China. In this study, we report the genomic analysis of a new JEV strain, CQ11-66, isolated from a pediatric patient in Chongqing, China.

FINDINGS

Virus isolation was carried out in BHK-21 cells. Nested PCR was used to detect and isolate the JEV strain, and computer analysis of phylogenetic relationships, nucleic acid homology studies and deduction of the amino acid sequence were conducted using ClustalX (1.8) and Mega5 software. The JEV strain CQ11-66 was isolated from patient cerebrospinal fluid. The sequenced genome of CQ11-66 was 10,863 nucleotides in length, whereas other strains, such as SX09S-01, contain 10,965 nucleotides. Sequence comparison of the CQ11-66 polyprotein open reading frame (ORF) with those of 21 other JEV strains revealed that the nucleotide sequence divergence ranged from 1.68% to 18.46%. Sequence analysis of the full-length CQ11-66 E gene sequence with those of 30 other JEV isolates also identified nucleotide divergence, ranging from 1.69% to 18.74%. Phylogenetic analyses indicated that the CQ11-66 strain belonged to genotype III.

CONCLUSIONS

JEV genotype III still circulates in Chongqing and it is therefore important for active surveillance of JEV genotype III to be conducted in the pediatric population.

Molecular characterization of Japanese encephalitis virus strains prevalent in Chinese swine herds

Japanese encephalitis virus (JEV) is the leading cause of viral encephalitis in Asia and domestic pigs serve as the amplifying hosts. In the present study, the full genomic sequences of two JEV strains (HEN0701 and SH0601) isolated from pigs in China were determined and compared with other 12 JEV strains deposited in GenBank. These two strains had an 88.8% nucleotide sequence similarity and 97.9% deduced amino acid sequence homology. HEN0701 had high nucleotide sequence and high amino acid sequence identity with genotype I (GI) strains, while SH0601 had high nucleotide sequence and high amino acid sequence identity with GIII strains at both the gene and full genome levels. Further phylogenetic analysis showed that HEN0701 belonged to the JEV GI group and SH0601 was classified as a GIII strain. Analysis of codon usage showed there were a few differences between the GI and GIII strains in nucleotide composition and codon usage for the open reading frames.

Characterization of a serine-to-asparagine substitution at position 123 in the Japanese encephalitis virus E protein

Amino acid position 123 in the E protein of Japanese encephalitis virus (JEV) determines viral growth properties and pathogenicity. The majority of JEV strains have a serine residue at this position (E(123S)); however, JEV with an asparagine residue (E(123N)) has also been isolated. To compare the growth properties and pathogenicity of E(123S) and E(123N) JEV, we produced recombinant JEV with a serine-to-asparagine substitution at position 123 (rJEV-Mie41-E(S123N)) in the E(123S)-type strain Mie/41/2002 background. The growth rate of rJEV-Mie41-E(S123N) was similar to that of Mie/41/2002 in mammalian and mosquito cell lines. Mouse challenge experiments showed that there was only a slight difference in neuroinvasiveness between the parent strain (Mie/41/2002) and rJEV-Mie41-E(S123N). Thus, our results indicate that the Ser-to-Asn substitution in the JEV E protein has weak impact on viral growth properties in vitro or on pathogenicity in vivo.

Development and application of an indirect enzyme-linked immunosorbent assay for serological survey of Japanese encephalitis virus infection in dogs

Japanese encephalitis virus (JEV) causes serious acute encephalitis in humans and horses. Although dogs are good sentinels for assessing the risk of JEV infection to humans, a virus neutralization test has been the only method available for measuring the levels of JEV antibody in dogs. In this study, an indirect enzyme-linked immunosorbent assay (ELISA) using purified viral particles as an antigen, was developed for serological survey of JEV infection in dogs. In dogs inoculated experimentally with JEV, the ELISA detected anti-JEV IgM 3 days after infection, with IgM levels peaking 7 days after infection. Anti-JEV IgG was detected 14 days after infection and peaked on 21-28 days after infection. Virus neutralization titers correlated with anti-JEV immunoglobulins measured by the ELISA. To test the utility of the new assay, the seroprevalence of JEV infection among 102 dogs in Kyushu, Japan, was examined by IgG ELISA and by virus neutralization. The correlation coefficient between the IgG ELISA and virus neutralization was 0.813 (p<0.001); comparison of the IgG ELISA and virus neutralization showed a sensitivity and specificity of 82% and 98%, respectively. The IgG ELISA was used to survey dogs in Bangkok, Thailand and 51% of these dogs were found seropositive for JEV. These data suggest that in the capital city of Thailand, the risk of infection with JEV remains high.

Molecular phylogenetic and evolutionary analysis of Japanese encephalitis virus in China

We elucidated the molecular epidemiology and evolution of Japanese encephalitis virus (JEV) strains isolated from 1949 to 2009 in China in this study. Three genotypes (I, III, V) were confirmed to be co-circulating in China in both high- and low-prevalence areas. Genotype III consisted of two clades (mainland clade and Taiwan clade). Compared to the mainland clade, genotype I and the Taiwan clade were newly introduced and evolved more rapidly. We also demonstrated that JEV strains in China, especially those in the mainland clade, were not only under purifying selection, but also probably under positive selection (aa 227 and 408 in the envelope protein).

Identification and characterization of the short variable region of the Japanese encephalitis virus 3' NTR

Since the 1980s, the Japanese encephalitis virus (JEV) variants with slightly short variable regions (VR) of the 3' non-translated region (NTR) have been found; however, the implications of these short VR remain unclear. We recently identified two novel types of short VR (5 and 9 nt shorter than that of major group of genotype I JEV strains) of genotype I JEV isolates. To elucidate the impact of these short VR on the replication and virulence of JEV, we generated five recombinant JEV viruses: M41-d5 and M41-d9 have deletions in the VR that correspond to those observed in some recent JEV isolates, M41-d5d9 has both the 5- and 9-nt deletions in the VR, M41-d27 has a large deletion that encompasses both the 5- and 9-nt deletion regions, and M41-a13 has a 13-nt sequence insertion of the genotype III JEV strain Beijing-1 into the parent genotype I JEV strain Mie/41/2002 genome. The recombinant viruses and the parent virus, except for the M41-d27 mutant, showed similar growth properties in mammalian and mosquito cell lines. Mouse challenge experiments indicated that no significant differences among the recombinant viruses M41-d5d9, M41-d27, M41-a13, and the parent virus. Our results suggest that the short VR in JEV 3' NTR do not affect its growth in vitro or its pathogenicity in mice.

Isolation and molecular characterization of genotype 1 Japanese encephalitis virus, SX09S-01, from pigs in China

Background

Pigs play a critical role in Japanese encephalitis virus (JEV) transmission between mosquitos and humans. In 2009, lots of piglets developed symptom of viral encephalitis in a pig farm in Yunchen, Shanxi province.

Methods

Virus isolation was carried out in BHK-21 cells. Immunohistochemistry, RT-PCR and indirect immunofluorescent assay were used to identify the newly isolated virus. The complete genome of one isolate (SX09S-01 strain) was sequenced and analyzed. Two phylogenetic trees were constructed on the basis of the 24 full-length JEV genomes and 62 E genes mostly selected from China.

Results

JEV SX09S-01 strain was isolated from piglets. Sequence analysis indicates that the completed genome sequences of this strain consists of 10965 nucleotides and there are 13 nucleotides deletion in the 3' nontranslated variable region. Compared with other JEV strains, homology ranges from 99.1% (XJ69) to 74.1% (XZ0934) and 99.6% (XJ69) to 91.1% (XZ0934) on the level of nucleotide and amino acid sequences, respectively. Phylogenetic trees show that SX09S-01 strain belongs to genotype I and it is most closely related to the XJ69 strain.

Conclusions

Genotype I of JEV still circulates in Yuncheng and it is thus important for active surveillance on genotype I of JEV from the swine population.

An amino acid substitution (V3I) in the Japanese encephalitis virus NS4A protein increases its virulence in mice, but not its growth rate in vitro

Our previous studies have shown that the Japanese encephalitis virus (JEV) strain Mie/40/2004 is the most virulent of the strains isolated by us in Japan from 2002 to 2004. Comparison of the amino acid sequence of Mie/40/2004 with those of low-virulence strains revealed that an isoleucine residue at position 3 of the Mie/40/2004 NS4A protein may increase viral pathogenicity. A recombinant virus with a single valine-to-isoleucine substitution (V3I) at position 3 in the low-virulence Mie/41/2002 background (rJEV-Mie41-NS4AV3I) exhibited increased virulence in mice compared with the Mie/41/2002 parent strain. The V3I mutation did not affect virus growth in several cell lines. These results demonstrate that the isoleucine at position 3 in the NS4A protein of Mie/40/2004 is responsible for its high virulence in vivo. This is the first report to show that an amino acid substitution in a flavivirus NS4A protein alters viral pathogenicity in mice.

Continuity and change of Japanese encephalitis virus in Toyama Prefecture, Japan

To determine the mechanisms of maintenance and evolution of Japanese encephalitis virus (JEV) in a temperate zone, we attempted to isolate JEV from mosquitoes and pigs in Toyama Prefecture, Japan. A total of 87 JEVs were isolated from female Culex tritaeniorhynchus mosquitoes and pigs during 2005-2009. The prevalence of JEV in Toyama Prefecture was seasonally late in comparison with that of the virus during 1966-1972. Furthermore, JEVs were isolated after the peak in the number of female Cx. tritaeniorhynchus. Among JEV strains isolated in this study, two distinct groups were observed within genotype I of the phylogeny generated from nucleotide sequence information derived from the envelope and capsid/premembrane genes: strains belonging to the major type were isolated during 2005-2009, and strains from the minor type were isolated only in 2007. The major type has exhibited gradual change in its envelope and capsid/premembrane genes, and all isolates obtained in 2008 and 2009 had a novel deletion of seven nucleotides in the variable region of the 3'-untranslated region.

Combating Japanese encephalitis: Vero-cell derived inactivated vaccines and the situation in Japan

Japanese encephalitis (JE) is a major public health threat in Asia, because of its high mortality and high incidence of psychoneurological sequelae in survivors. It is caused by JE virus (JEV) infection, transmitted by vector mosquitoes. The disease is vaccine preventable and has been well controlled in some countries. Since no specific antivirals have been approved, prevention with vaccine is important in this disease. This article provides a general overview of JE and JEV, but special focus has been put on recently developed Vero cell-derived formalin-inactivated JE vaccines, and the situation in Japan relating to these vaccines. In Japan, where JE has been well controlled, the strong governmental recommendation of the mouse brain-derived vaccine for routine immunization was suspended in 2005, owing to a patient suffering severe postvaccination events. In 2010, the recommendation was reinstated, targeting a limited population utilizing a Vero cell-derived vaccine.

Dogs as sentinels for human infection with Japanese encephalitis virus

Because serosurveys of Japanese encephalitis virus (JEV) among wild animals and pigs may not accurately reflect risk for humans in urban/residential areas, we examined seroprevalence among dogs and cats. We found that JEV-infected mosquitoes have spread throughout Japan and that dogs, but not cats, might be good sentinels for monitoring JEV infection in urban/residential areas.

Needle-free jet injection of small doses of Japanese encephalitis DNA and inactivated vaccine mixture induces neutralizing antibodies in miniature pigs and protects against fetal death and mummification in pregnant sows

Japanese encephalitis (JE) virus causes abortion and stillbirth in swine, and encephalitis in humans and horses. We have previously reported that immunogenicity of a DNA vaccine against JE was synergistically enhanced in mice by co-immunization with a commercial inactivated JE vaccine (JEVAX) under a needle-free injection system. Here, we found that this immunization strategy was also effective in miniature pigs. Because of the synergism, miniature pigs immunized twice with a mixture of 10 μg of DNA and a 1/100 dose of JEVAX developed a high neutralizing antibody titer (1:190 at 90% plaque reduction assay). Even using 1 μg of DNA, 3 of 4 pigs developed neutralizing antibodies. Following challenge, all miniature pigs with detectable neutralizing antibodies were protected against viremia. Pregnant sows inoculated with 10 or 1 μg of DNA mixed with JEVAX (1/100 dose) developed antibody titers of 1:40-1:320. Following challenge, fetal death and mummification were protected against in DNA/JEVAX-immunized sows.

Molecular epidemiology of Japanese encephalitis virus circulating in South Korea, 1983-2005

We sequenced the envelope (E) gene of 17 strains of the Japanese encephalitis virus (JEV) isolated in South Korea in 1983-2005 and compared the sequences with those from previously reported strains. Our results show the remarkable genetic stability of the E gene sequence in Korean JEV strains. Five pairs of E gene sequences from 10 Korean strains were identical, despite geographical differences and a maximum five-year time span. Sequence comparisons with other Asian strains revealed that the Korean strains are closely related to those from China, Japan, and Vietnam. Genotype 3 strains were predominant in Korea before 1993, when genotype 1 strain K93A07 was first isolated. The two genotypes were detected simultaneously in 1994 but since then, only genotype 1 has been isolated in South Korea. Thus, the genotype change occurred according to the year of isolation rather than the geographical origin.

Phylogeographic analysis of the migration of Japanese encephalitis virus in Asia

Japanese encephalitis virus (JEV) is one of the zoonotic arboviruses, and causes encephalitis in humans. Our phylogenetic analysis revealed that some phylogenetic subclusers were distributed as widely as continental Asia to Japan (subclusters 1-A-1, 1-A-2, 1-A-3, 1-A-5, 3-A-1, 3-A-2, 3-B-1 and 3-D). However, two subclusters were only isolated in Japan (1-A-6 and 1-A-7). These data suggest that multiple populations of JEV have migrated from southeast Asia and continental east Asia to Japan and, in Japan, JEV can overwinter and settle. In this article, we aim to explain the ecological factors related to the overseas expansion, migration and overwintering of JEV.

Molecular evolution of Japanese encephalitis virus isolates from swine in Oita, Japan during 1980-2009

In order to identify the patterns of genetic change of Japanese encephalitis virus (JEV) strains circulating in Oita, the complete envelope (E) gene has been sequenced for 35 isolates from swine in a 30-year span. Based on nucleotide and deduced amino acid sequences, the genetic variation was examined, phylogeny was estimated and selection pressures were also analyzed. This study demonstrated that the major genotype (G) of JEV isolates had shifted from GIII to GI in the mid-1990s in Oita. The intensities of selection acting on the Oita GIII and GI strains were found to be almost same. It suggests that the intensity of selection might not be the reason for such a genotype shift observed in Oita. Pairwise comparisons revealed the high conservation of the E gene at the protein level. Compared with the Oita GIII strains, all the Oita GI strains shared four amino acid changes at E129 (T-M), E222 (A-S), E327 (S-T) and E366 (A-S). Among all 70 JEV isolates involved in this paper, the GI strains shared only one amino acid change at E222 (A-S) in comparison with the GIII strains. No strong evidence for positive selection was found, the JEV evolution has generally been subject to strong purifying selection, but one ongoing evolutionary pathway was found to be under relaxed purifying selection in Oita. This study is a localized example of JEV molecular evolution in nature.