Unique humoral immune response of pigs to repeated natural Japanese encephalitis virus infections: an amplifying host perspective

Japanese encephalitis virus (JEV) is the leading cause of viral encephalitis in the Asia-Pacific region. Amplification of JEV in pigs is a potent driver for spillover of the infection to humans, and hence monitoring of virus dynamics in pigs can provide insights into JEV ecology. To study the dynamics of natural JEV infection in a tropical region, two groups of immunologically naïve pigs consisting of six animals per group were kept as sentinels on two different farms in the district of Thanjavur, Tamil Nadu, India. In a longitudinal study conducted from May 2022 to October 2023, nested RT-PCR and indirect ELISA were used to track the dynamics of JEV and the humoral response in pigs. Synchronous and asynchronous seroconversion in pigs was recorded on two different farms with different management practices. Repeated infections with JEV were recorded in all of the sentinel animals throughout the study period, irrespective of the season. Phylogenetic analysis revealed the presence of JEV genotype III in the region. It was observed that the IgG response to natural JEV infection did not last long, which might have been the reason for repeated infections in the sentinel animals. The longest period during which IgG was present at detectable levels in this study was two months, after which the pigs could once again amplify the virus. A significant positive correlation was found between wind speed and JEV incidence in sentinel animals. Our results offer a different perspective on the relationship between JEV and its amplifying host that contradicts the assumption that pre-immune pigs are resistant to JEV amplification. Our findings could have a major impact on our understanding of the ecology of JEV in tropical regions, where there is a high burden of JE despite coordinated prevention efforts that have relied on achieving a long-lasting immune response.

Genotypic characterization of Japanese encephalitis virus circulating in swine population of India: Genotype-III still in dominance

Swine is considered as a suitable sentinel to predict Japanese encephalitis virus (JEV) outbreaks in humans. The present study was undertaken to determine the circulating genotypes of JEV in swine population of India. A total of 702 swine serum samples from four states of western, northern, northern-temperate, and north-eastern zones of India were screened by real-time RT-PCR targeting envelope gene of JEV, which showed positivity of 35.33%. The viral copy number ranged from 3 copies to 6.3 × 10⁴ copies/reaction. Subsequently, the capsid/prM structural gene region of JEV positive samples was amplified by nested RT-PCR, sequenced, and genetically characterized. The phylogenetic analysis of the partial sequences of the capsid gene of 42 JEV positive samples showed that they all belonged to genotype-III (G-III) of JEV. Notably, JEV positive swine samples showed high nucleotide identity with human isolates from China and Nepal which explains the probable spillover of infection between neighboring countries probably by migratory birds. The novel mutations were observed in JEV positive sample B8 at C54 position (Phe → Ser), and JEV positive sample K50 at C62 (Thr → Ala) and C65 (Leu → Pro) positions which were absent from other JEV isolates reported till now. The mutation at the C66 position (Leu → Ser) observed in live attenuated vaccine SA14-14-2 strain was not found in JEV positive samples of our study. The detection of the G-III JE virus from climatically diverse states of India reinforces the need to continue the ongoing human vaccination program in India by extending vaccine coverage in temperate states.

Japanese Encephalitis Virus Genotype III Strains Detection and Genome Sequencing from Indian Pig and Mosquito Vector

Japanese encephalitis viruses (JEVs) are globally prevalent as deadly pathogens in humans and animals, including pig, horse and cattle. Japanese encephalitis (JE) still remains an important cause of epidemic encephalitis worldwide and exists in a zoonotic transmission cycle. Assam is one of the highly endemic states for JE in India. In the present study, to understand the epidemiological status of JE circulating in pigs and mosquito, particularly in Assam, India, molecular detection of JEV and the genome sequencing of JEV isolates from pigs and mosquitoes was conducted. The genome analysis of two JEV isolates from pigs and mosquitoes revealed 7 and 20 numbers of unique points of polymorphism of nucleotide during alignment of the sequences with other available sequences, respectively. Phylogenetic analysis revealed that the isolates of the present investigation belong to genotype III and are closely related with the strains of neighboring country China. This study highlights the transboundary nature of the JEV genotype III circulation, which maintained the same genotype through mosquito-swine transmission cycles.

Effectiveness of Live-Attenuated Genotype III Japanese Encephalitis Viral Vaccine against Circulating Genotype I Viruses in Swine

Expansion of genotype I (GI) Japanese encephalitis viruses (JEV) has resulted in the replacement of the dominant genotype III (GIII) viruses, raising serious public health concerns for using GIII virus-derived vaccines to effectively control JEV epidemics. Therefore, this study used swine as the model to estimate the effectiveness of GIII live-attenuated vaccine against GI virus infection by comparing the incidence of stillbirth/abortion in gilts from vaccinated and non-vaccinated pig farms during the GI-circulation period. In total, 389 and 213 litters of gilts were recorded from four vaccinated and two non-vaccinated pig farms, respectively. All viruses detected in the aborted fetuses and mosquitoes belonged to the GI genotype during the study period. We thus estimated that the vaccine effectiveness of GIII live-attenuated vaccine against GI viruses in naive gilts based on the overall incidence of stillbirth/abortion and incidence of JEV-confirmed stillbirth/abortion was 65.5% (50.8–75.7%) and 74.7% (34.5–90.2%), respectively. In contrast to previous estimates, the GIII live-attenuated vaccine had an efficacy of 95.6% (68.3–99.4%) to prevent the incidence of stillbirth/abortion during the GIII-circulating period. These results indicate that the vaccine effectiveness of GIII live-attenuated JEV vaccine to prevent stillbirth/abortion caused by GI viruses is lower than that against GIII viruses.

Effectiveness of a single dose of Japanese encephalitis vaccine among adults, Assam, India, 2012-2018

BACKGROUND

Japanese encephalitis virus (JEV) remains the major etiology of encephalitis throughout Asia. In India, the state of Assam alone contributes more than one-third of the national burden of JE. Between 2011 and 2014, a single dose of JE vaccine SA 14-14-2 (LAJEV) was administered among adults aged 15-65 years residing in Sivasagar and Dibrugarh districts of Assam, India. We monitored the trend of JE incidence between 2009 and 2018 using JE surveillance data, estimated the long-term effectiveness of the single dose of LAJEV and estimated the coverage of JE vaccine in two districts.

METHODS

We compared the JE vaccination status of laboratory-confirmed hospitalized JE patients (case) and age, sex and locality matched healthy individuals (controls) to estimate the effectiveness of single dose of JE vaccine. We used surveillance data for 2009-2018 to calculate the incidence of JE among adults. We conducted a community-based survey to estimate the coverage of JE vaccine in the two districts.

RESULTS

A total of 452 laboratory-confirmed JE case-patients and 904 matched healthy controls were enrolled in the study between 2012 and 2018. The effectiveness of a single dose of JE vaccine over the 7-year period was 77.0 (95% CI: 67.0-83.0). Vaccine effectiveness decreased from 91% (95% CI: 73.0-97.0) in first year of vaccination to 71% (95% CI: 21.0-90.0) at six years post-vaccination. The incidence of adults JE cases declined from 10.5 per 100,000 in the pre-vaccination period to 5.7 per 100,000 in the years following vaccination. The coverage of vaccine among adults in two districts was 40.1% (36.8-43.5).

CONCLUSIONS

A single dose of JE vaccine offered adequate protection for at least six years. Conducting mass vaccination campaigns periodically would further reduce the incidence of JE in endemic districts in Assam.

Field-deployable molecular diagnostic platform for arbovirus detection in Aedes aegypti

BACKGROUND

Surveillance of mosquito infection status is critical for planning and deployment of proper mosquito control initiatives. Point-of-care (POC) detection assays are necessary for monitoring the infection prevalence and geographical range of viruses in mosquito vector populations. We therefore assessed the novel real-time PCR (qPCR) bCUBE (Hyris, London, UK) molecular diagnostic system as a tool for virus detection.

METHODS

Aedes aegypti Rps17 was used to validate and determine correlation coefficient for the novel bCUBE qPCR system to a laboratory standard StepOnePlus real-time PCR system (Applied Biosystems, Waltham, MA, USA). Experimentally infected Ae. aegypti were quantified for Zika (ZIKV) and dengue virus serotype 2 (DENV2) viral genomic RNA. Infection prevalence was compared to plaque assay.

RESULTS

We developed and validated a novel qPCR system for the detection of ZIKV and DENV2 using the real-time qPCR system bCUBE. With bCUBE-based qRT-PCR, viral genomic RNA could be detected in individually infected Ae. aegypti mosquitoes and in pools of 5, 10 or 15 mosquitoes.

CONCLUSIONS

The portable qPCR bCUBE diagnostic system is capable of detecting Zika and dengue virus in mosquitoes and therefore has potential as a practical field-deployable diagnostic test for vector-borne disease surveillance programmes.

CD8+ T cells are crucial for humoral immunity establishment by SA14-14-2 live attenuated Japanese encephalitis vaccine in mice

The live attenuated SA14-14-2 Japanese encephalitis (JE) vaccine is a historical vaccine that protects against JE. Despite its extensive use, the mechanism of protective immunity conferred by the SA14-14-2 vaccine is not well established. Here, we used mouse models to understand the mechanism of the development of humoral immunity against the vaccine. The vaccine induces robust GC responses within a week postimmunization. In lethal virus challenge, we show that CD4⁺ T cells alone, but not CD8⁺ T cells, are sufficient to confer vaccine-mediated protection. However, the CD4-mediated protection was potentiated in the presence of vaccine-primed CD8⁺ T cells. Employing CD8-deficient mice, we show that both the protective traits of CD4⁺ T cells and the quality of antibody response to the vaccine are impaired in absence of CD8⁺ T cells. We further demonstrate that the poor protective immune response induced by the vaccine in absence of CD8⁺ T cells is mainly due to the impaired differentiation and function of follicular Th cells, leading to suboptimal GC reaction. Our study highlights an unprecedented role of CD8⁺ T cells in the establishment of humoral responses to the vaccine. By elucidating underlying cellular determinants of vaccine-induced protective immunity, our work has implications for rational design of vaccines against JE virus and related flaviviruses.

Genetic diversity of Orientia tsutsugamushi strains circulating in Northeast India

Background

Scrub typhus, caused by the intracellular bacteria Orientia tsutsugamushi is widely distributed in Southeast Asian countries with antigenically divergent strains reported across the Asia-Pacific belt. The present study was conducted to characterize the circulating strains of Orientia tsutsugamushi prevailing in two Northeastern states of India-the gateway to most Southeast Asian countries.

Methods

A total of 278 (98 clinical and 180 field collected) scrub typhus positive blood samples collected from December 2014 to December 2016 were subjected for amplification of partial 56 KDa, 47 KDa and 16SrRNA genes of Orientia.

Results

Highest number of PCR positives were obtained for 56 KDa gene (17.3%); followed by 11.2% for 47 KDa gene and 5.1% for 16S rRNA gene. High degree of genetic diversity was identified among the identified strains, especially within the 56 KDa gene. Different strains of Orientia circulate in the northeastern part of India, with a pre-dominance of Karp-like strains. Independently branched isolates formed distinct clades, suggesting the possibility of a new strain type of Orientia.

Conclusion

This study provides insight into the genetic and evolutionary relationship of Orientia strains prevalent in this part of the country. Understanding the regional genetic diversity is crucial for its implications in vaccine developments strategies as well as sero-diagnostics.

Accession numbers

KU163366, KY594249, KY594248, KY594251, KU163359, KU163361, KU163363, KU163369, KY594250, KP067915, KU163373, KU163372, KU163370, KU163364, KU163362, KY594247, KY594252, KU163360, KU163365, KU163367, KU163368, KU163371, KX1555826, KY594257, KY594255, KY594256, KX155825, KX155829, KX155827, KX155828, KY594254, KY594253, KY594258, KY583503, KY583499, KY583501, KY583500, KY583502.

Enhanced cytopathic effect of Japanese encephalitis virus strain SA14-14-2: Probable association of mutation in amino acid of its envelope protein

Japanese encephalitis (JE) is a mosquito-borne viral disease. It is a global public health concern since it causes an acute encephalitis syndrome (AES). A large number of JE/AES cases are reported to occur in areas with established or developing JE vaccination program. Partial vaccine coverage and emergence of new variants of Japanese encephalitis virus (JEV) might be playing an important role. The envelope protein (E) of JEV is a major antigenic determinant and responsible for immunogenic responses as well as membrane fusion and virion assembly. In the present study, we have characterized the JEV live attenuated vaccine strain SA14-14-2 in baby hamster kidney cells (BHK-21). The vaccine strain showed enhanced replication following its passage in BHK-21 cells. Nucleotide sequence analysis of the E protein gene of the cell-culture adapted vaccine strain showed an important point mutation. The mutation in the E protein gene was identical to its wild-type parent strain SA14. This study suggests the possibility of reversion mutation and exaltation of vaccine strains following adaptation in the host cells.

Seroepidemiology of rickettsial infections in Northeast India

BACKGROUND

Resurgence of scrub typhus was reported in Northeast India in 2010 after a gap of 67 years since World War II. However, the presence of other rickettsial infections remained unknown from this region. A seroepidemiological investigation was undertaken in the scrub typhus affected areas from 2013-2015 in Assam, Arunachal Pradesh and Nagaland to assess the exposure to other rickettsial diseases besides scrub typhus.

METHODS

Samples were collected from people residing in scrub typhus reporting areas. Serology was performed by an indirect ELISA for the three rickettsial agents' viz., scrub typhus group orientiae (STGO), spotted fever group rickettsiae (SFGR) and typhus group rickettsiae (TGR). A sample with total net absorbance ≥1.000 was considered as positive. An entomological survey was also carried out in the affected areas.

RESULTS

Overall, 1265 human blood samples were collected, of which 30.8% (n=390), 13.8% (175) and 4.2% (53) had antibodies against STGO, SFGR and TGR respectively. Presence of antibodies against more than one of the rickettsial groups was also detected. Among the arthropods collected, chiggers of Leptotrombidium deleinse, fleas belonging to Ctenocephalides felis and Pulex irritans, ticks belonging to Rhipicephalus microplus, Haemaphysalis spp. were predominant. Candidatus Rickettsia senegalensis was detected in C. felis.

CONCLUSIONS

Our findings confirm wide circulation of rickettsial infections and their probable vectors in the northeast region of India.Accession numbers: KU163367, KU163368, KU499847, KU499848.

A large outbreak of Japanese encephalitis predominantly among adults in northern region of West Bengal, India

Unusual rise of acute encephalitis syndrome cases (AES) were reported in July 2014 in the northern region of West Bengal, India. Investigations were carried out to characterize the outbreak and to identify the associated virus etiology. This observational study is based on 398 line listed AES cases, mostly (70.8%, 282/398) adults, with case fatality ratio of 28.9% (115/398). Japanese encephalitis virus infection was detected in 134 (49.4%) among 271 AES cases tested and most of them (79.1%, 106/134) were adults. The study reports a large outbreak of genotype III Japanese encephalitis among adults in northern region of West Bengal, India. J. Med. Virol. 88:2004-2011, 2016. © 2016 Wiley Periodicals, Inc.