Comparison of Neutralizing Antibody Titers against Japanese Encephalitis Virus Genotype V Strain with Those against Genotype I and III Strains in the Sera of Japanese Encephalitis Patients in Japan in 2016

Development of Colloidal Gold-Based Immunochromatographic Strips for Rapid Detection and Surveillance of Japanese Encephalitis Virus in Dogs across Shanghai, China

Japanese encephalitis virus (JEV) causes acute encephalitis in humans and is of major public health concern in most Asian regions. Dogs are suitable sentinels for assessing the risk of JEV infection in humans. A neutralization test (NT) or an enzyme-linked immunosorbent assay (ELISA) is used for the serological detection of JEV in dogs; however, these tests have several limitations, and, thus, a more convenient and reliable alternative test is needed. In this study, a colloidal gold immunochromatographic strip (ICS), using a purified recombinant EDIII protein, was established for the serological survey of JEV infection in dogs. The results show that the ICSs could specifically detect JEV antibodies within 10 min without cross-reactions with antibodies against other canine viruses. The test strips could detect anti-JEV in serum with dilution up to 640 times, showing high sensitivity. The coincidence rate with the NT test was higher than 96.6%. Among 586 serum samples from dogs in Shanghai examined using the ICS test, 179 (29.98%) were found to be positive for JEV antibodies, and the high seropositivity of JEV in dogs in China was significantly correlated with the season and living environment. In summary, we developed an accurate and economical ICS for the rapid detection of anti-JEV in dog serum samples with great potential for the surveillance of JEV in dogs.

Laboratory evaluation of ELISA and indirect immunofluorescence assay in response to emergence of Japanese encephalitis virus genotype IV in Australia

The unexpected recent emergence of Japanese encephalitis virus (JEV) genotype IV in multiple southern states of Australia necessitated an evaluation of JEV serological tests suitable for diagnosing acute infection and for seroprevalence studies. This study examined the analytical and clinical performance of two high-throughput JEV assays, Euroimmun immunofluorescence assay (IFA) and Euroimmun enzyme-linked immunosorbent assay (ELISA), across four cohorts; (1) surveillance of piggery workers in outbreak areas, (2) surveillance of residents in outbreak areas, (3) acute JEV infection and (4) post-JEV vaccination. ELISA and IFA IgM demonstrated minimal cross-reactivity (0-1.8%) with other endemic flaviviruses, with high sensitivity (100%) for acute JEV infection in this low endemicity setting. Differences in IgG serodynamics between the two assays suggest convalescent and paired testing with IgM are critical in diagnosing acute infection. High assay concordance was observed between ELISA and IFA when used in serosurveillance (97.4% agreement, Cohen' κ 0.74 [95% CI 0.614-0.860]) and vaccination cohorts (91.1% agreement, Cohen's κ 0.806 [95% CI 0.672-0.941]). In conclusion, this study highlights the clinical & epidemiological applications and limitations of these two commercial JEV assays.

Analysis of cross-reactivity among flaviviruses using sera of patients with dengue showed the importance of neutralization tests with paired serum samples for the correct interpretations of serological test results for dengue

Dengue is a febrile illness caused by the dengue virus (DENV) that belongs to the genus Flavivirus in the family Flaviviridae. Cross-reactivity between flaviviruses poses a challenge while interpreting serological test results. In the present study, the cross-reactivity of sera of the patients with dengue, who traveled from Japan to DENV-endemic countries, was analyzed by using an enzyme-linked immunosorbent assay (ELISA) and neutralization test (NT). Sixteen serum samples were collected from patients with dengue and were tested for: i) IgM antibodies against Zika virus (ZIKV), West Nile virus (WNV), Japanese encephalitis virus (JEV), and tick-borne encephalitis virus (TBEV) using IgM ELISA, ii) IgG antibody against TBEV using IgG ELISA, and iii) neutralizing antibody against ZIKV, WNV, TBEV, and JEV. Among the 16 samples tested using ELISA, seven samples were IgM-positive for at least one of the other flaviviruses, and nine samples were IgG-positive for TBEV. Neutralizing antibody titers (NATs) against ZIKV, WNV, and TBEV were one-fourth or lower than those against the causative DENV in all samples. The NATs against JEV were one-fourth or lower than those against the causative DENV in six convalescent-phase serum sample among the seven convalescent-phase serum samples. The NAT against DENV of the residual one convalescent-phase serum was similar to that against JEV and that against JEV of its relevant acute-phase serum sample. These results showed that NTs with paired serum samples are important to correctly interpret the serological test results for DENV.

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.

Novel Antiviral Efficacy of Hedyotis diffusa and Artemisia capillaris Extracts against Dengue Virus, Japanese Encephalitis Virus, and Zika Virus Infection and Immunoregulatory Cytokine Signatures

Currently, there are no specific therapeutics for flavivirus infections, including dengue virus (DENV) and Zika virus (ZIKV). In this study, we evaluated extracts from the plants Hedyotis diffusa (HD) and Artemisia capillaris (AC) to determine the antiviral activity against DENV, ZIKV, and Japanese encephalitis virus (JEV). HD and AC demonstrated inhibitory activity against JEV, ZIKV, and DENV replication and reduced viral RNA levels in a dose-responsive manner, with non-cytotoxic concentration ranging from 0.1 to 10 mg/mL. HD and AC had low cytotoxicity to Vero cells, with CC₅₀ values of 33.7 ± 1.6 and 30.3 ± 1.7 mg/mL (mean ± SD), respectively. The anti-flavivirus activity of HD and AC was also consistent in human cell lines, including human glioblastoma (T98G), human chronic myeloid leukemia (K562), and human embryonic kidney (HEK-293T) cells. Viral-infected, HD-treated cells demonstrated downregulation of cytokines including CCR1, CCL26, CCL15, CCL5, IL21, and IL17C. In contrast, CCR1, CCL26, and AIMP1 were elevated following AC treatment in viral-infected cells. Overall, HD and AC plant extracts demonstrated flavivirus replication inhibitory activity, and together with immunoregulatory cytokine signatures, these results suggest that HD and AC possess bioactive compounds that may further be refined as promising candidates for clinical applications.

Seroepidemiological surveys of tick-borne encephalitis virus and novel tick-borne viruses in wild boar in Nagasaki, Japan

In Japan, tick-borne viruses such as tick-borne encephalitis virus (TBEV) and severe fever with thrombocytopenia syndrome virus have been identified in humans, animals, and ticks. In addition, novel tick-borne viruses have been isolated from ticks in Japan. This study aimed to determine the seroprevalence of TBEV and novel viruses, particularly Tofla virus (TFLV), Kabuto Mountain virus (KAMV), and Muko virus (MUV) in wild boar in Nagasaki, Japan. Enzyme-linked immunosorbent assays and neutralization tests were performed to detect antibodies against each virus. Wild boar serum tested positive for antibodies against KAMV, TFLV, and TBEV, but not MUV. This study revealed the seroprevalence of newly identified tick-borne viruses and TBEV in animals residing in the Nagasaki area. The seroprevalence of these viruses in sentinel animals may inform policies aimed at preventing tick-borne virus disease outbreaks.

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.

Japanese Encephalitis- and Dengue-Associated Acute Encephalitis Syndrome Cases in Myanmar

This study was conducted to find the burden of dengue virus (DENV) and Japanese encephalitis virus (JEV) among children under the age of 13, who presented with acute encephalitis syndrome at Mandalay Children Hospital in Myanmar in 2013. Molecular and serological investigations were performed on 123 cerebrospinal fluid (CSF) samples collected from these patients. By neutralization tests and/or virus isolation, four (3.3%) JEV- and one DENV-associated encephalitis cases (0.8%) were confirmed. Antibody titer against JEV Genotype 3 was the highest among the laboratory-confirmed JEV cases. One strain of DENV-1 with Genotype 1 was isolated from the CSF sample of the dengue encephalitis patient; this was similar to the virus circulating in the study area and neighboring countries. This study shows that flaviviruses are important pathogens causing encephalitis in Myanmar. Active disease surveillance, vector control, and vaccination programs should be enforced to reduce the morbidity and mortality caused by flavivirus encephalitis.

Review of Emerging Japanese Encephalitis Virus: New Aspects and Concepts about Entry into the Brain and Inter-Cellular Spreading

Japanese encephalitis virus (JEV) is an emerging flavivirus of the Asia-Pacific region. More than two billion people live in endemic or epidemic areas and are at risk of infection. Recently, the first autochthonous human case was recorded in Africa, and infected birds have been found in Europe. JEV may spread even further to other continents. The first section of this review covers established and new information about the epidemiology of JEV. The subsequent sections focus on the impact of JEV on humans, including the natural course and immunity. Furthermore, new concepts are discussed about JEV’s entry into the brain. Finally, interactions of JEV and host cells are covered, as well as how JEV may spread in the body through latently infected immune cells and cell-to-cell transmission of virions or via other infectious material, including JEV genomic RNA.

Analysis of cross-reactivity between flaviviruses with sera of patients with Japanese encephalitis showed the importance of neutralization tests for the diagnosis of Japanese encephalitis

Japanese encephalitis (JE) is one of the most important viral encephalitis in Asia. JE is caused by the Japanese encephalitis virus (JEV), which belongs to the genus Flavivirus, family Flaviviridae. The diagnosis of JE is usually based on serological assays, and it has been reported that cross-reactivity between flaviviruses has complicated the interpretations of results from serological assays. Therefore, analysis of the cross-reactivity is an important subject for serological diagnosis of JE and other diseases caused by flaviviruses. In the present study, the cross-reactivity of the sera of patients with JE to other flaviviruses was analyzed using enzyme-linked immunosorbent assay (ELISA) and neutralization tests. Sixteen serum samples were collected from patients with JE and were tested for: i) IgM antibody against West Nile virus (WNV), dengue virus (DENV), zika virus (ZIKV), and tick-borne encephalitis virus (TBEV) using IgM-ELISA, ii) IgG antibody against DENV and TBEV using IgG-ELISA, and iii) neutralization tests with DENV 1-4, ZIKV, TBEV, and WNV. Out of the 16 samples tested using ELISA, 11 and 14 samples were positive for IgM and IgG, respectively, against at least one of the other flaviviruses. In neutralization tests, neutralizing potency against DENV, ZIKV, or TBEV was not detected in any samples. Although 13 samples showed neutralizing potency against WNV, their neutralizing antibody titers were equal to or less than one-eighth of those against JEV. These results show that neutralization tests are more specific than ELISA, indicating the importance of the neutralization tests in the diagnosis of JE.

Neutralization Potency of Sera from Vietnamese Patients with Japanese Encephalitis (JE) against Genotypes I and V JE Viruses

Japanese encephalitis virus (JEV) is classified into 5 genotypes (GI, GII, GIII, GIV, and GV), and the GI and GIII strains are the most widely distributed in JE endemic areas. In recent years, GV JEV has been detected in China and Korea, suggesting that GV JEV may invade other JE endemic areas, including Vietnam, and that more attention should be paid to the JEV strains circulating in these areas. In this study, we investigated the neutralization ability of the sera collected from 22 Vietnamese patients with JE who lived in northern Vietnam against the GI and GV JEV strains. In most cases, the ratios of the titer against GV to that against GI (GV:GI) were equal to or less than 1:4. However, the titer against GV JEV was equivalent (1:1) to that against GI JEV in only a few cases, and no serum had a ratio higher than 1:1. Thus, our results did not show convincing evidence that GV JEV was emerging in northern Vietnam in 2014.