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

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.

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.

Aptamers isolated against mosquito-borne pathogens

Mosquito-borne diseases are a major threat to public health. The shortcomings of diagnostic tools, especially those that are antibody-based, have been blamed in part for the rising annual morbidity and mortality caused by these diseases. Antibodies harbor a number of disadvantages that can be clearly addressed by aptamers as the more promising molecular recognition elements. Aptamers are defined as single-stranded DNA or RNA oligonucleotides generated by SELEX that exhibit high binding affinity and specificity against a wide variety of target molecules based on their unique structural conformations. A number of aptamers were developed against mosquito-borne pathogens such as Dengue virus, Zika virus, Chikungunya virus, Plasmodium parasite, Francisella tularensis, Japanese encephalitis virus, Venezuelan equine encephalitis virus, Rift Valley fever virus and Yellow fever virus. Intrigued by these achievements, we carry out a comprehensive overview of the aptamers developed against these mosquito-borne infectious agents. Characteristics of the aptamers and their roles in diagnostic, therapeutic as well as other applications are emphasized.

How Central Is the Domestic Pig in the Epidemiological Cycle of Japanese Encephalitis Virus? A Review of Scientific Evidence and Implications for Disease Control

Despite the existence of human vaccines, Japanese encephalitis (JE) remains the leading cause of human encephalitis in Asia. Pigs are described as the main amplifying host, but their role in JE epidemiology needs to be reassessed in order to identify and implement efficient control strategies, for both human and animal health. We aimed to provide a systematic review of publications linked to JE in swine, in terms of both individual and population characteristics of JE virus (JEV) infection and circulation, as well as observed epidemiological patterns. We used the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement to select and analyze relevant articles from the Scopus database, 127 of which were included in the review. Pigs are central, but the implication of secondary hosts cannot be ruled out and should be further investigated. Although human vaccination cannot eradicate the virus, it is clearly the most important means of preventing human disease. However, a better understanding of the actual involvement of domestic pigs as well as other potential JEV hosts in different JEV epidemiological cycles and patterns could help to identify additional/complementary control measures, either by targeting pigs or not, and in some specific epidemiological contexts, contribute to reduce virus circulation and protect humans from JEV infection.

Japanese encephalitis virus infection, diagnosis and control in domestic animals

Japanese encephalitis virus (JEV) is a significant cause of neurological disease in humans throughout Asia causing an estimated 70,000 human cases each year with approximately 10,000 fatalities. The virus contains a positive sense RNA genome within a host-derived membrane and is classified within the family Flaviviridae. Like many flaviviruses, it is transmitted by mosquitoes, particularly those of the genus Culex in a natural cycle involving birds and some livestock species. Spill-over into domestic animals results in a spectrum of disease ranging from asymptomatic infection in some species to acute neurological signs in others. The impact of JEV infection is particularly apparent in pigs. Although infection in adult swine does not result in symptomatic disease, it is considered a significant reproductive problem causing abortion, still-birth and birth defects. Infected piglets can display fatal neurological disease. Equines are also infected, resulting in non-specific signs including pyrexia, but occasionally leading to overt neurological disease that in extreme cases can lead to death. Veterinary vaccination is available for both pigs and horses. This review of JEV disease in livestock considers the current diagnostic techniques available for detection of the virus. Options for disease control and prevention within the veterinary sector are discussed. Such measures are critical in breaking the link to zoonotic transmission into the human population where humans are dead-end hosts.

European Aedes albopictus and Culex pipiens Are Competent Vectors for Japanese Encephalitis Virus

Background

Japanese encephalitis virus (JEV) is the causative agent of Japanese encephalitis, the leading cause of viral encephalitis in Asia. JEV transmission cycle involves mosquitoes and vertebrate hosts. The detection of JEV RNA in a pool of Culex pipiens caught in 2010 in Italy raised the concern of a putative emergence of the virus in Europe. We aimed to study the vector competence of European mosquito populations, such as Cx. pipiens and Aedes albopictus for JEV genotypes 3 and 5.

Findings

After oral feeding on an infectious blood meal, mosquitoes were dissected at various times post-virus exposure. We found that the peak for JEV infection and transmission was between 11 and 13 days post-virus exposure. We observed a faster dissemination of both JEV genotypes in Ae. albopictus mosquitoes, when compared with Cx. pipiens mosquitoes. We also dissected salivary glands and collected saliva from infected mosquitoes and showed that Ae. albopictus mosquitoes transmitted JEV earlier than Cx. pipiens. The virus collected from Ae. albopictus and Cx. pipiens saliva was competent at causing pathogenesis in a mouse model for JEV infection. Using this model, we found that mosquito saliva or salivary glands did not enhance the severity of the disease.

Conclusions

In this study, we demonstrated that European populations of Ae. albopictus and Cx. pipiens were efficient vectors for JEV transmission. Susceptible vertebrate species that develop high viremia are an obligatory part of the JEV transmission cycle. This study highlights the need to investigate the susceptibility of potential JEV reservoir hosts in Europe, notably amongst swine populations and local water birds.

Japanese encephalitis virus (JEV) is the leading cause of viral encephalitis in Asia. JEV is maintained in a cycle involving mosquitoes and vertebrate hosts, mainly pigs and wading birds. Humans can be infected when bitten by an infected mosquito. Culex tritaeniorhynchus is the main vector of the disease in tropical and subtropical areas. The recent detection of JEV in birds and mosquitoes collected in Northern Italy has led us to evaluate the putative emergence of this arboviral disease in Europe. For this purpose, we have tested the competence of European populations of Cx. pipiens and Aedes albopictus to transmit this virus in a laboratory setting. We showed that these local mosquitoes could be infected and were capable of transmitting a pathogenic virus to mice. It is thus urgent to evaluate the risks of JEV emergence in European regions displaying a favorable environment for mosquito vectors, susceptible pigs and wading birds.

Electroporation enhances protective immune response of a DNA vaccine against Japanese encephalitis in mice and pigs

Japanese encephalitis virus (JEV) is a pathogenic cause of Japanese Encephalitis (JE), which is a zoonotic disease transmitted by mosquitoes and amplified by pigs. Infection of JEV may lead to severe neurological sequelae, even death in humans and reproductive disorders in pigs. Vaccination is the only way to control JEV infection in humans. For pigs play important role in the JEV transmission cycle, developing a new veterinary vaccine is considered as a useful strategy for cutting off the transmission route of JEV. We have previously reported that DNA vaccine pCAG-JME, expressing prM-E proteins of JEV, is effective in mice through intramuscular injection (IM). However, the poor immunogenicity, due to low expression of immunogen, is the major obstacle for the development of DNA vaccine in large animals. In the present study, therefore, we immunized mice and pigs with pCAG-JME intramuscularly accompanied with electroporation (EP) stimulation, the attractive gene delivery approach. As compared with IM, EP-mediated vaccination markedly increased the expression of immunogen in the injection site and induced a dose- and time-dependent immune response. 100% survival rate was observed in groups vaccinated with doses ranged from 10 to 100μg, indicating that 10μg of DNA with EP for individual was enough for inducing effective protection in mice. Surprisingly, survival rate and end-point titers of anti-JEV antibodies were higher in mice even at lower dose of DNA (5μg) than that in mice inoculated 100μg through IM. Notably, the prM-E antigens also induced high antibody response in pig, while the neutralizing antibody titer achieved 1:320. Our results suggested that EP-mediated DNA immunization might act as an effective strategy against JEV, at least in pig, and that EP has a potential application prospect in DNA vaccination.

Japanese encephalitis virus tropism in experimentally infected pigs

Pigs are considered to be the main amplifying host for Japanese encephalitis virus (JEV), and their infection can correlate with human cases of disease. Despite their importance in the ecology of the virus as it relates to human cases of encephalitis, the pathogenesis of JEV in pigs remains obscure. In the present study, the localization and kinetics of virus replication were investigated in various tissues after experimental intravenous infection of pigs. The data demonstrate a rapid and broad spreading of the virus to the central nervous system (CNS) and various other organs. A particular tropism of JEV in pigs not only to the CNS but also for secondary lymphoid tissue, in particular the tonsils with the overall highest viral loads, was observed. In this organ, even 11 days post infection, the latest time point of the experiment, no apparent decrease in viral RNA loads and live virus was found despite the presence of a neutralizing antibody response. This was also well beyond the clinical and viremic phase. These results are of significance for the pathogenesis of JEV, and call for further experimental studies focusing on the cellular source and duration of virus replication in pigs.

Vector-free transmission and persistence of Japanese encephalitis virus in pigs

Japanese encephalitis virus (JEV), a main cause of severe viral encephalitis in humans, has a complex ecology, composed of a cycle involving primarily waterbirds and mosquitoes, as well as a cycle involving pigs as amplifying hosts. To date, JEV transmission has been exclusively described as being mosquito-mediated. Here we demonstrate that JEV can be transmitted between pigs in the absence of arthropod vectors. Pigs shed virus in oronasal secretions and are highly susceptible to oronasal infection. Clinical symptoms, virus tropism and central nervous system histological lesions are similar in pigs infected through needle, contact or oronasal inoculation. In all cases, a particularly important site of replication are the tonsils, in which JEV is found to persist for at least 25 days despite the presence of high levels of neutralizing antibodies. Our findings could have a major impact on the ecology of JEV in temperate regions with short mosquito seasons.

Japanese encephalitis virus (JEV) is primarily transmitted between mosquitoes and birds but can also infect pigs. Here the authors demonstrate that JEV, which was thought to be spread exclusively by mosquitoes, can be transmitted between pigs through a direct contact.

A Lentiviral Vector Expressing Japanese Encephalitis Virus-like Particles Elicits Broad Neutralizing Antibody Response in Pigs

Background

Japanese encephalitis virus (JEV) is the major cause of viral encephalitis in Southeast Asia. Vaccination of domestic pigs has been suggested as a “one health” strategy to reduce viral disease transmission to humans. The efficiency of two lentiviral TRIP/JEV vectors expressing the JEV envelope prM and E glycoproteins at eliciting protective humoral response was assessed in a mouse model and piglets.

Methodology/Principal Findings

A gene encoding the envelope proteins prM and E from a genotype 3 JEV strain was inserted into a lentiviral TRIP vector. Two lentiviral vectors TRIP/JEV were generated, each expressing the prM signal peptide followed by the prM protein and the E glycoprotein, the latter being expressed either in its native form or lacking its two C-terminal transmembrane domains. In vitro transduction of cells with the TRIP/JEV vector expressing the native prM and E resulted in the efficient secretion of virus-like particles of Japanese encephalitis virus. Immunization of BALB/c mice with TRIP/JEV vectors resulted in the production of IgGs against Japanese encephalitis virus, and the injection of a second dose one month after the prime injection greatly boosted antibody titers. The TRIP/JEV vectors elicited neutralizing antibodies against JEV strains belonging to genotypes 1, 3, and 5. Immunization of piglets with two doses of the lentiviral vector expressing JEV virus-like particles led to high titers of anti-JEV antibodies, that had efficient neutralizing activity regardless of the JEV genotype tested.

Conclusions/Significance

Immunization of pigs with the lentiviral vector expressing JEV virus-like particles is particularly efficient to prime antigen-specific humoral immunity and trigger neutralizing antibody responses against JEV genotypes 1, 3, and 5. The titers of neutralizing antibodies elicited by the TRIP/JEV vector are sufficient to confer protection in domestic pigs against different genotypes of JEV and this could be of a great utility in endemic regions where more than one genotype is circulating.

Japanese encephalitis virus is the etiologic agent of the most medically important viral encephalitis in South Asia with thousands of deaths per year. The virus is maintained in an enzootic cycle between Culex mosquitoes and amplifying vertebrate hosts, such as wild boars and pigs. Vaccination of domestic pigs has been suggested as a strategy to reduce viral disease transmission to humans, in line with the now-called “One Health” concept. Lentiviral gene transfer vectors represent a novel vaccination platform with an unprecedented ability to induce robust humoral immunity in various animal species. In our study, we demonstrated that immunization of pigs with a recombinant lentiviral vector expressing virus-like particles of Japanese encephalitis virus is particularly efficient at eliciting specific humoral immunity. The titers of neutralizing antibodies elicited by the lentiviral vector are sufficient to confer protection in domestic pigs against the different genotypes of Japanese encephalitis virus observed in Asia.