The reemerging and outbreak of genotypes 4 and 5 of Japanese encephalitis virus

Partial protective efficacy of the current licensed Japanese encephalitis live vaccine against the emerging genotype I Japanese encephalitis virus isolated from sheep

Introduction

Vaccination remains the most effective strategy for preventing and controlling Japanese encephalitis (JE). The Japanese encephalitis virus (JEV) seroconversion has been documented in sheep and goats across various countries, with occasional fatal cases occurring among sheep on farms in China. Despite the widespread use of attenuated live vaccines, the efficacy of these vaccines in protecting sheep against JE remains uncertain. This study aimed to assess the protective efficacy of currently available attenuated vaccines against genotype I (GI) JEV strains isolated from sheep using a mouse challenge model.

Methods

In this study, vaccination-challenge experiments were conducted using a mouse challenge model to assess the efficacy of attenuated vaccines. The specific vaccines tested were the SA14-14-2 (GI) and SD12-F120 (GI) attenuated live vaccines. The neutralizing antibodies generated by these vaccines were titrated to evaluate their levels of protection. Mice were immunized with high, medium, or low doses of the vaccines and then challenged with either homologous or heterologous JEV strains. The challenge strains included the SH2201 (GI) and N28 (GIII) strains. Viremia levels and the development of encephalitis lesions were monitored as indicators of protection.

Results

The neutralizing antibody titers against the sheep-derived SH2201 (GI) strain were significantly lower in mice immunized with the SA14-14-2 (GIII) vaccine compared to those receiving the SD12-F120 (GI) vaccine. Immunization with high and medium doses of SA14-14-2 (GIII) vaccine provided complete protection against challenge with the homologous N28 (GIII) strain but only partial protection against the heterologous SH2201 (GI) strain. Mice immunized with medium and low doses of SA14-14-2 (GIII) vaccine showed varying levels of viremia and developed characteristic encephalitis lesions after being challenged with the heterologous SH2201 (GI) strain. Conversely, mice immunized with high and medium doses of the SD12-F120 (GI) vaccine exhibited 100% protection against the challenge with the homologous SH2201 (GI) strain.

Discussion

The results of this study suggest that while the SA14-14-2 (GIII) attenuated live vaccine offers partial protection against sheep-derived GI strains, it is not fully effective against heterologous strains like SH2201 (GI). This highlights a significant gap in the ability of the current vaccines to protect across different JEV genotypes and host species. In contrast, the SD12-F120 (GI) vaccine demonstrated stronger protection against the homologous SH2201 (GI) strain. These findings indicate a pressing need for the development of new vaccination strategies that can provide broader and more effective protection against JE, particularly in diverse host species and against a wide range of JEV genotypes.

Characterization of genotype V Japanese encephalitis virus isolates from Republic of Korea

Japanese encephalitis (JE), caused by the Japanese encephalitis virus (JEV) infection, continues to pose significant public health challenges worldwide despite efficient vaccines. The virus is classified into five genotypes, among which genotype V (GV) was not detected for a long period after its initial isolation in 1952, until reports emerged from China and the Republic of Korea (ROK) since 2009. The characteristics of the virus are crucial in estimating its potential epidemiological impact. However, characterization of GV JEVs has so far been limited to two strains: Muar, the original isolate, and XZ0934, isolated in China. Two additional ROK GV JEV isolates, NCCP 43279 and NCCP 43413, are currently available, but their characteristics have not been explored. Our phylogenetic analysis revealed that GV virus sequences from the ROK segregate into two clades. NCCP 43279 and NCCP 43413 belong to different clades and exhibit distinct in vitro phenotypes. NCCP 43279 forms larger plaques but demonstrates inefficient propagation in cell culture compared to NCCP 43413. In vivo, NCCP 43279 induces higher morbidity and mortality in mice than NCCP 43413. Notably, NCCP 43279 shows more severe blood-brain barrier damage, suggesting superior brain invasion capabilities. Consistent with its higher virulence, NCCP 43279 displays more pronounced histopathological and immunopathological outcomes. In conclusion, our study confirms that the two ROK isolates are not only classified into different clades but also exhibit distinct in vitro and in vivo characteristics.

Long-term co-circulation of multiple arboviruses in southeast Australia revealed by xeno-monitoring and viral whole-genome sequencing

Arbovirus surveillance of wild-caught mosquitoes is an affordable and sensitive means of monitoring virus transmission dynamics at various spatial-temporal scales, and emergence and re-emergence during epidemic and interepidemic periods. A variety of molecular diagnostics for arbovirus screening of mosquitoes (known as xeno-monitoring) are available, but most provide limited information about virus diversity. Polymerase chain reaction (PCR)-based screening coupled with RNA sequencing is an increasingly affordable and sensitive pipeline for integrating complete viral genome sequencing into surveillance programs. This enables large-scale, high-throughput arbovirus screening from diverse samples. We collected mosquitoes in CO2-baited light traps from five urban parks in Brisbane from March 2021 to May 2022. Mosquito pools of ≤200 specimens were screened for alphaviruses and flaviviruses using virus genus-specific primers and reverse transcription quantitative PCR (qRT-PCR). A subset of virus-positive samples was then processed using a mosquito-specific ribosomal RNA depletion method and then sequenced on the Illumina NextSeq. Overall, 54,670 mosquitoes representing 26 species were screened in 382 pools. Thirty detections of arboviruses were made in 28 pools. Twenty of these positive pools were further characterized using RNA sequencing generating 18 full-length genomes. These full-length sequences belonged to four medically relevant arboviruses: Barmah Forest, Ross River, Sindbis-like, and Stratford viruses. Phylogenetic and evolutionary analyses revealed the evolutionary progression of arbovirus lineages over the last 100 years, demonstrating that different epidemiological, immunological, and evolutionary processes may actively shape the evolution of Australian arboviruses. These results underscore the need for more genomic surveillance data to explore the complex evolutionary pressures acting on arboviruses. Overall, our findings highlight the effectiveness of our methodology, which can be applied broadly to enhance arbovirus surveillance in various ecological contexts and improve understanding of transmission dynamics.

Experimental Infections of Pigs with Japanese Encephalitis Virus Genotype 4

The emergence of Japanese encephalitis virus (JEV) in eastern Australia in 2022 caused extensive reproductive disease in pigs and is a threat to public health. Groups of weaned piglets were experimentally infected with the Australian outbreak strain of JEV (genotype 4). All pigs challenged at 5 weeks of age were infected after an intradermal injection of 1 × 105.5 (n = 4) or 1 × 104.5 TCID50/pig (n = 5). Intranasal instillation was less effective at this age, infecting 3/4 pigs with the same higher dose and 1/5 with the lower dose. Intradermal injection using 1 × 105.0 TCID50/pig also infected 9/9 pigs at 11 weeks of age. Infection in all cases was confirmed by qRT-PCR of blood samples, which identified a viremia peak at 3-4 days and detected JEV-specific antibodies as early as 5 days after the challenge. The detection of JEV in oral and nasal swabs and in saliva from chew ropes was less consistent. JEV was detected in the tonsils of 21/22 infected pigs and was isolated from the tonsils of 9/9 pigs sampled 19 days after the challenge at 11 weeks of age. The infected pigs showed no clinical signs other than pyrexia on Days 4-6. Histopathology consistent with JEV infection was evident in the nervous tissues of all but two pigs sampled 28 days after the challenge and was characterized by meningitis, encephalitis and gliosis throughout the brain. Serological studies showed extensive cross-reactivity between JEV and Murray Valley encephalitis virus using blocking ELISAs. However, the determination of limiting-dilution titres allowed for the identification of the infecting virus. This in vivo infection model will be useful in evaluating JEV vaccines and for comparative pathogenesis studies with other JEV genotypes.

Detection and evolutionary characterization of arboviruses in mosquitoes and biting midges on Hainan Island, China, 2019-2023

We conducted a large-scale survey of arboviruses in mosquitoes and biting midges to assess the presence and spread of mosquito-borne pathogens currently circulating on Hainan Island, China. RT-PCR assays were used to detect the arbovirus species, distribution, and infection rates in mosquitoes and biting midges. Cell inoculation and high throughput sequencing were performed to isolate the viruses and assemble full viral genomes. Phylogenetic analysis was conducted to identify the viral genotypes and evolutionary relationships with known viruses. During 2019-2023, 32,632 mosquitoes and 21,000 biting midges were collected from 14 of 18 cities/counties on Hainan Island. Japanese encephalitis virus (JEV) was detected in Culex mosquitoes from five cities/counties, where the minimum infection rate (MIR) was 1.6 (0.6-2.6) per 1,000 females tested. Tembusu virus (TMUV) was detected in Culex mosquitoes from three cities/counties with MIR1.0 (0-2.2) per 1,000. Getah virus (GETV) was detected in Armigeres mosquitoes from Qionghai city with MIR 7.1 (0-15.2) per 1,000. Oya virus (OYAV) and Bluetongue virus (BTV) were detected in biting midges from Wanning city with MIRs of 0.4 (0-1.2) and 0.1 (0-10.2) per 1,000, respectively. Three JEV strains were isolated and clustered within the genotype I group, which is presently the dominant genotype in China. Three TMUV strains were isolated for the first time on Hainan Island that belonged to Cluster 3. Three isolated GETVs were identified as Group 3. BTV was reported for the first time on Hainan Island, and the complete genome for one BTV strain was successfully assembled, which was classified as serotype 1 based on the sequences of segment 2. These results stress the need to develop adequate surveillance plan measures to better control the public health threat of arboviruses carried by mosquitoes and biting midges in local regions.

Single-Dose Immunogenic DNA Vaccines Coding for Live-Attenuated Alpha- and Flaviviruses

Single-dose, immunogenic DNA (iDNA) vaccines coding for whole live-attenuated viruses are reviewed. This platform, sometimes called immunization DNA, has been used for vaccine development for flavi- and alphaviruses. An iDNA vaccine uses plasmid DNA to launch live-attenuated virus vaccines in vitro or in vivo. When iDNA is injected into mammalian cells in vitro or in vivo, the RNA genome of an attenuated virus is transcribed, which starts replication of a defined, live-attenuated vaccine virus in cell culture or the cells of a vaccine recipient. In the latter case, an immune response to the live virus vaccine is elicited, which protects against the pathogenic virus. Unlike other nucleic acid vaccines, such as mRNA and standard DNA vaccines, iDNA vaccines elicit protection with a single dose, thus providing major improvement to epidemic preparedness. Still, iDNA vaccines retain the advantages of other nucleic acid vaccines. In summary, the iDNA platform combines the advantages of reverse genetics and DNA immunization with the high immunogenicity of live-attenuated vaccines, resulting in enhanced safety and immunogenicity. This vaccine platform has expanded the field of genetic DNA and RNA vaccines with a novel type of immunogenic DNA vaccines that encode entire live-attenuated viruses.