Past, present, and future of Japanese encephalitis

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.

Inactivated genotype 1 Japanese encephalitis vaccine for swine

PURPOSE

Japanese encephalitis is a reproductive disorder caused by Japanese encephalitis virus (JEV) in swine. Recent genotype (G) shift phenomenon (G3 to G1) in the Asia-wide has posed a challenge for proper prevention by the current vaccine strain. Thus, new kinds of JEV G1 vaccines with enhanced immunogenicity have been required for pigs.

MATERIALS AND METHODS

Recombinant porcine granulocyte monocyte-colony stimulating factor (reporGM-CSF) protein was expressed in Spodoptera frugiperda (Sf-9) cells using baculovirus expression system. Two kinds of trials with inactivated JEV vaccines containing IMS1313 adjuvant (Seppic, France) were prepared with or without reporGM-CSF protein. Safety and immunogenicity of the pigs inoculated with the JEV vaccines via intramuscular route was evaluated for 28 days after inoculation.

RESULTS

Mice, guinea pigs, and fattening pigs inoculated with the inactivated vaccine showed no signs for 14 and 21 days. Both hemagglutination inhibition and plaque reduction neutralizing antibody titers were significantly higher in pigs immunized with the vaccine containing reporGM-CSF protein after boosting. However, on the side of vaccine efficacy, most mice (87%) immunized with the inactivated JEV vaccine survived after virulent JEV challenge. Whereas the group with the vaccine containing reporGM-CSF protein showed lower protective effects than the vaccine alone for the biological activity of the GM-CSF depending on species specific.

CONCLUSION

Our data indicate that animals inoculated with the JEV vaccines was safe and pigs inoculated with inactivated JEV vaccine containing reporGM-CSF protein showed higher humoral immune responses than that of inactivated JEV vaccine without reporGM-CSF protein.

A spatial and temporal analysis of Japanese encephalitis in mainland China, 1963-1975: a period without Japanese encephalitis vaccination

More than a million Japanese encephalitis (JE) cases occurred in mainland China from the 1960s to 1970s without vaccine interventions. The aim of this study is to analyze the spatial and temporal pattern of JE cases reported in mainland China from 1965 to 1973 in the absence of JE vaccination, and to discuss the impacts of climatic and geographical factors on JE during that period. Thus, the data of reported JE cases at provincial level and monthly precipitation and monthly mean temperature from 1963 to 1975 in mainland China were collected. Local Indicators of Spatial Association analysis was performed to identify spatial clusters at the province level. During that period, The epidemic peaked in 1966 and 1971 and the JE incidence reached up to 20.58/100000 and 20.92/100000, respectively. The endemic regions can be divided into three classes including high, medium, and low prevalence regions. Through spatial cluster analysis, JE epidemic hot spots were identified; most were located in the Yangtze River Plain which lies in the southeast of China. In addition, JE incidence was shown to vary among eight geomorphic units in China. Also, the JE incidence in the Loess Plateau and the North China Plain was showed to increase with the rise of temperature. Likewise, JE incidence in the Loess Plateau and the Yangtze River Plain was observed a same trend with the increase of rainfall. In conclusion, the JE cases clustered geographically during the epidemic period. Besides, the JE incidence was markedly higher on the plains than plateaus. These results may provide an insight into the epidemiological characteristics of JE in the absence of vaccine interventions and assist health authorities, both in China and potentially in Europe and Americas, in JE prevention and control strategies.

Type-I interferon response affects an inoculation dose-independent mortality in mice following Japanese encephalitis virus infection

Background

The laboratory mouse model is commonly employed to study the pathogenesis of encephalitic flaviviruses such as Japanese encephalitis virus (JEV). However, it is known that some strains of these viruses do not elicit a typical mortality dose response curve from this organism after peripheral infection and the reason for it has not yet been fully understood. It is suggested that induction of more vigorous Type-I IFN (IFN-I) response might control early virus dissemination following increasing infectious challenge doses of the virus. Thus, the objective of this study was to examine this suggested role of IFN-I in the mortality of mice infected with various doses of JEV.

Methods

Inbred 129 mice and their IFNAR KO (A129) mice were subcutaneously inoculated with 10⁰, 10², 10⁴ or 10⁶ pfu of JaOArS982 strain of JEV. Mice were weighed daily and observed for clinical signs. Virus titers in the brains and spleens of JEV-infected mice were determined by plaque forming assays. The upregulated mRNA levels of genes related to IFN-I response of mice were examined by real-time PCR.

Results

The mortality rates of 129 mice infected with JaOArS982 did not significantly increase despite the increase in inoculation dose and no significant difference of viral loads was observed between their brains. However, there was clear elevation of the mRNA levels of interferon regulatory factor (IRF)3, IRF7, IRF9, MDA5 and RIG-I at 24 hours post-infection depending on the inoculation dose. In A129 mice, length of survival days and the viral loads of spleen and brain were observed to be inoculation dose-dependent.

Conclusions

From these results, it is suggested that early IFN-I response elicited by high inoculation doses of JEV provides an anti-viral effect during the early phase of infection. Accordingly, virus replication is counteracted by IFN-I response at each increasing inoculation dose resulting in the interference of impending severe disease course or fatal outcome; hence, this might explain the inoculation dose-independent mortality in mice caused by Japanese encephalitis virus.

Major emerging and re-emerging zoonoses in China: a matter of global health and socioeconomic development for 1.3 billion

Emerging and re-emerging zoonoses are a significant public health concern and cause considerable socioeconomic problems globally. The emergence of severe acute respiratory syndrome (SARS), highly pathogenic avian influenza (HPAI) H5N1, avian influenza H7N9, and severe fever with thrombocytopenia syndrome (SFTS), and the re-emergence of rabies, brucellosis, and other zoonoses have had a significant effect on the national economy and public health in China, and have affected other countries. Contributing factors that continue to affect emerging and re-emerging zoonoses in China include social and environmental factors and microbial evolution, such as population growth, urbanization, deforestation, livestock production, food safety, climate change, and pathogen mutation. The Chinese government has devised new strategies and has taken measures to deal with the challenges of these diseases, including the issuing of laws and regulations, establishment of disease reporting systems, implementation of special projects for major infectious diseases, interdisciplinary and international cooperation, exotic disease surveillance, and health education. These strategies and measures can serve as models for the surveillance and response to continuing threats from emerging and re-emerging zoonoses in other countries.

Entomological investigations into an epidemic of Japanese encephalitis (JE) in northern districts of West Bengal, India (2011-2012)

BACKGROUND & OBJECTIVES

Japanese encephalitis (JE) is one of the most important arboviral diseases of human beings with outbreaks in many parts of Southeast Asia including India. We present the entomological findings of an outbreak occurred in northern part of West Bengal during 2011-2012 with special emphasis on the role of JE vectors in different seasons.

METHODS

Adult mosquito collections were made with the help of mouth aspirators, aided by flash lights during day time resting inside human and animal habitations as indoor, and resting outside field grasses, bushes, underneath of culverts and bridges as outdoor, and in and around the pig enclosures and cattle sheds during dusk period in JE affected villages from Cooch Behar, Dakshin Dinajpur, Darjeeling and Jalpaiguri districts in North West Bengal. In all study villages, a long handled with enamel bowl dipper was used to obtain immature stages of mosquitoes from various breeding habitats.

RESULTS

A total of 19 different types of mosquito breeding habitats were examined for vectors of JE. From these habitats, 23.7 per cent were positive for breeding during the study period. Overall, nine different species were recorded through emergence, but none was positive for JE virus when subjected for detection of virus. Adult mosquitoes of more than 50 per cent of the potential JE vector species obtained through dusk and the rest through indoor and outdoor collections in all seasons. Altogether, 27 different species were recorded. Most of these were JE vectors.

INTERPRETATION & CONCLUSIONS

Our results showed that in addition to Cx. vishnui subgroup, detection of JE virus antigen in Cx. quinquefasciatus indicated the possible maintenance of JE virus in nature through poor vector mosquitoes throughout the year. Since, all potential vector species reported elsewhere in India were also found in this region and fluctuated in density in different seasons, a proper integrated vector control programme needs to be implemented to control JE transmission.

Japanese encephalitis risk and contextual risk factors in southwest China: a Bayesian hierarchical spatial and spatiotemporal analysis

It is valuable to study the spatiotemporal pattern of Japanese encephalitis (JE) and its association with the contextual risk factors in southwest China, which is the most endemic area in China. Using data from 2004 to 2009, we applied GISmapping and spatial autocorrelation analysis to analyze reported incidence data of JE in 438 counties in southwest China, finding that JE cases were not randomly distributed, and a Bayesian hierarchical spatiotemporal model identified the east part of southwest China as a high risk area. Meanwhile, the Bayesian hierarchical spatial model in 2006 demonstrated a statistically significant association between JE and the agricultural and climatic variables, including the proportion of rural population, the pig-to-human ratio, the monthly precipitation and the monthly mean minimum and maximum temperatures. Particular emphasis was placed on the time-lagged effect for climatic factors. The regression method and the Spearman correlation analysis both identified a two-month lag for the precipitation, while the regression method found a one-month lag for temperature. The results show that the high risk area in the east part of southwest China may be connected to the agricultural and climatic factors. The routine surveillance and the allocation of health resources should be given more attention in this area. Moreover, the meteorological variables might be considered as possible predictors of JE in southwest China.

Dynamics of the emergence and establishment of a newly dominant genotype of Japanese encephalitis virus throughout Asia

In recent years, genotype I (GI) of Japanese encephalitis virus (JEV) has displaced genotype III (GIII) as the dominant virus genotype throughout Asia. In this study, the largest collection of GIII and GI envelope gene-derived viral sequences assembled to date was used to reconstruct the spatiotemporal chronology of genotype displacement throughout Asia and to determine the evolutionary and epidemiological dynamics underlying this significant event. GI consists of two clades, GI-a and GI-b, with the latter being associated with displacement of GIII as the dominant JEV genotype throughout Asia in the 1990s. Phylogeographic analysis indicated that GI-a diverged in Thailand or Cambodia and has remained confined to tropical Asia, whereas GI-b diverged in Vietnam and then dispersed northwards to China, where it was subsequently dispersed to Japan, Korea, and Taiwan. Molecular adaptation was detected by more than one method at one site (residue 15), and coevolution was detected at two pairs of sites (residues 89 to 360 and 129 to 141) within the GI E gene protein alignment. Viral multiplication and temperature sensitivity analyses in avian and mosquito cells revealed that the GI-b isolate JE-91 had significantly higher infectivity titers in mosquito cells from 24 to 48 h postinfection than did the GI-a and GIII isolates. If the JE-91 isolate is indeed representative of GI-b, an increased multiplicative ability of GI-b viruses compared to that of GIII viruses early in mosquito infection may have resulted in a shortened extrinsic incubation period that led to an increased number of GI enzootic transmission cycles and the subsequent displacement of GIII.

IMPORTANCE

Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, represents the most significant etiology of childhood viral neurological infection in Asia. Despite the existence of effective vaccines, JEV is responsible for an estimated 68,000 human cases and a reported 10,000 to 15,000 deaths annually. Phylogenetic studies divided JEV into five geographically and epidemiologically distinct genotypes (GI to GV). GIII has been the source of numerous JEV epidemics throughout history and was the most frequently isolated genotype throughout most of Asia from 1935 until the 1990s. In recent years, GI has displaced GIII as the most frequently isolated virus genotype. To date, the mechanism of this genotype replacement has remained unknown. In this study, we have identified genetic determinants underlying the genotype displacement as it unfolded across Asia. JEV provides a paradigm for other flaviviruses, including West Nile, yellow fever, and dengue viruses, and the critical role of the selective advantages in the mosquito vector.

Safety of Japanese encephalitis live attenuated vaccination in post-marketing surveillance in Guangdong, China, 2005-2012

We reviewed the adverse events following immunization of live attenuated Japanese encephalitis vaccine in Guangdong Province, China. During the period of 2005-2012, 23 million doses of live attenuated Japanese encephalitis vaccine were used and 1426 adverse events were reported (61.24 per million doses); of which, 570 (40%) were classified as allergic reactions (24.48 per million doses), 31 (2%) were neurologic events (1.33 per million doses), and 36 (2.5%) were diagnosed as serious adverse events (1.55 per million doses). This study suggests that the JEV-L has a reasonable safety profile, most adverse events are relatively mild, with relatively rare neurologic events being observed.

Estimating the burden of Japanese encephalitis virus and other encephalitides in countries of the mekong region

Diverse aetiologies of viral and bacterial encephalitis are widely recognized as significant yet neglected public health issues in the Mekong region. A robust analysis of the corresponding health burden is lacking. We retrieved 75 articles on encephalitis in the region published in English or in French from 1965 through 2011. Review of available data demonstrated that they are sparse and often derived from hospital-based studies with significant recruitment bias. Almost half (35 of 75) of articles were on Japanese encephalitis virus (JEV) alone or associated with dengue. In the Western Pacific region the WHO reported 30,000-50,000 annual JEV cases (15,000 deaths) between 1966 and 1996 and 4,633 cases (200 deaths) in 2008, a decline likely related to the introduction of JEV vaccination in China, Vietnam, or Thailand since the 1980s. Data on dengue, scrub typhus and rabies encephalitis, among other aetiologies, are also reviewed and discussed. Countries of the Mekong region are undergoing profound demographic, economic and ecological change. As the epidemiological aspects of Japanese encephalitis (JE) are transformed by vaccination in some countries, highly integrated expert collaborative research and objective data are needed to identify and prioritize the human health, animal health and economic burden due to JE and other pathogens associated with encephalitides.

A review of successful flavivirus vaccines and the problems with those flaviviruses for which vaccines are not yet available

Genus flavivirus comprises many important human pathogens causing public health problems worldwide. Some flavivirus infections are characterized by a relatively high mortality rate and/or high sequelae rate in survivors. Because most flavivirus life cycles are maintained between arthropod vectors and amplifying/reservoir hosts in the absence of humans, eradication of flaviviruses might be extremely difficult. Flavivirus vaccine development is considered a reasonable method to prevent flavivirus infections. Some vaccines have been successfully developed, but others have not, regardless of much effort. This review article describes currently available flavivirus vaccines against yellow fever, Japanese encephalitis, and tick-borne encephalitis. In addition, the current status of dengue and West Nile virus vaccine development is reviewed and problems regarding their development are discussed.

Peptide inhibitor of Japanese encephalitis virus infection targeting envelope protein domain III

Japanese encephalitis virus (JEV) is a major cause of acute viral encephalitis in both humans and animals. Domain III of the virus envelope glycoprotein (E DIII) plays an important role in the interaction of viral particles with host cell receptors to facilitate viral entry. Intervention of the interaction between E DIII and its cognate host cell receptor would provide an important avenue for inhibiting JEV infection. A phage display peptide library was therefore panned against E DIII, which resulted in the identification of several peptides. One peptide, named P3, inhibited JEV infection of BHK-21 cells with an IC₅₀ of ∼1 μM and an IC₉₀ at ∼100 μM. Further characterization revealed that P3 bound to E DIII with a K(d) of 6.06 × 10⁻⁶ M and inhibited JEV infection by interfering with viral attachment to cells. Based on in silico prediction by ZDOCK, P3 was found to interact with E DIII via a hydrophobic pocket, which was confirmed by the binding assay of P3 to the V357A mutant. P3 was hypothesized to bind to E DIII by interacting with the sties adjacent to the BC and DE loops, which might interfere with the binding of JEV to cellular receptors, thus impeding viral infection. This newly isolated peptide may represent a new therapeutic candidate for treatment of JEV.

Nitazoxanide inhibits the replication of Japanese encephalitis virus in cultured cells and in a mouse model

BACKGROUND

Japanese encephalitis virus (JEV) has a significant impact on public health. An estimated three billion people in 'at-risk' regions remain unvaccinated and the number of unvaccinated individuals in certain Asian countries is increasing. Consequently, there is an urgent need for the development of novel therapeutic agents against Japanese encephalitis. Nitazoxanide (NTZ) is a thiazolide anti-infective licensed for the treatment of parasitic gastroenteritis. Recently, NTZ has been demonstrated to have antiviral properties. In this study, the anti-JEV activity of NTZ was evaluated in cultured cells and in a mouse model.

METHODS

JEV-infected cells were treated with NTZ at different concentrations. The replication of JEV in the mock- and NTZ-treated cells was examined by virus titration. NTZ was administered at different time points of JEV infection to determine the stage at which NTZ affected JEV replication. Mice were infected with a lethal dose of JEV and intragastrically administered with NTZ from 1 day post-infection. The protective effect of NTZ on the JEV-infected mice was evaluated.

FINDINGS

NTZ significantly inhibited the replication of JEV in cultured cells in a dose dependent manner with 50% effective concentration value of 0.12 ± 0.04 μg/ml, a non-toxic concentration in cultured cells (50% cytotoxic concentration = 18.59 ± 0.31 μg/ml). The chemotherapeutic index calculated was 154.92. The viral yields of the NTZ-treated cells were significantly reduced at 12, 24, 36 and 48 h post-infection compared with the mock-treated cells. NTZ was found to exert its anti-JEV effect at the early-mid stage of viral infection. The anti-JEV effect of NTZ was also demonstrated in vivo, where 90% of mice that were treated by daily intragastric administration of 100 mg/kg/day of NTZ were protected from a lethal challenge dose of JEV.

CONCLUSIONS

Both in vitro and in vivo data indicated that NTZ has anti-JEV activity, suggesting the potential application of NTZ in the treatment of Japanese encephalitis.

Regional variation in pig farmer awareness and actions regarding Japanese encephalitis in Nepal: implications for public health education

Japanese encephalitis (JE) is a mosquito-borne zoonotic disease that has pigs as the major amplifying hosts. It is the most important cause of viral encephalitis in people in Nepal and is spreading in its geographic distribution in that country. Pig farming is increasing in Nepal due to reducing cultural biases against pigs and government programs to support pig farming for poverty alleviation. Major strategies for JE prevention and control include education, vector control, and immunization of people and pigs. This study used a survey of 400 pig farmers in 4 areas of Nepal with different JE and pig farming histories to explore regional variations in farmer awareness and actions towards JE, the association of awareness and actions with farm and farmer variables, and the implications of these associations for public health education. Exposure to JE risk factors was common across pig farms and pig farming districts but there were significant district level differences in knowledge and practices related to on-farm JE risk reduction. Social factors such as literacy, gender, and cultural practices were associated with farmer attitudes, knowledge and practices for JE control. JE vaccine uptake was almost non-existent and mosquito control steps were inconsistently applied across all 4 districts. Income was not a determining factor of the differences, but all farmers were very poor. The low uptake of vaccine and lack of infrastructure or financial capacity to house pigs indoors or away from people suggest that farmer personal protection should be a priority target for education in Nepal. This study re-enforces the need to attack root causes of people's personal disease prevention behaviours and take into account local variation in needs and capacities when designing health or agriculture education programs.

Epidemiology, geographical distribution, and economic consequences of swine zoonoses: a narrative review

We sought to review the epidemiology, international geographical distribution, and economic consequences of selected swine zoonoses. We performed literature searches in two stages. First, we identified the zoonotic pathogens associated with swine. Second, we identified specific swine-associated zoonotic pathogen reports for those pathogens from January 1980 to October 2012. Swine-associated emerging diseases were more prevalent in the countries of North America, South America, and Europe. Multiple factors were associated with the increase of swine zoonoses in humans including: the density of pigs, poor water sources and environmental conditions for swine husbandry, the transmissibility of the pathogen, occupational exposure to pigs, poor human sanitation, and personal hygiene. Swine zoonoses often lead to severe economic consequences related to the threat of novel pathogens to humans, drop in public demand for pork, forced culling of swine herds, and international trade sanctions. Due to the complexity of swine-associated pathogen ecology, designing effective interventions for early detection of disease, their prevention, and mitigation requires an interdisciplinary collaborative “One Health” approach from veterinarians, environmental and public health professionals, and the swine industry.

Biomarkers in Japanese encephalitis: a review

JE is a flavivirus generated dreadful CNS disease which causes high mortality in various pediatric groups. JE disease is currently diagnosed by measuring the level of viral antigens and virus neutralization IgM antibodies in blood serum and CSF by ELISA. However, it is not possible to measure various disease-identifying molecules, structural and molecular changes occurred in tissues, and cells by using such routine methods. However, few important biomarkers such as cerebrospinal fluid, plasma, neuro-imaging, brain mapping, immunotyping, expression of nonstructural viral proteins, systematic mRNA profiling, DNA and protein microarrays, active caspase-3 activity, reactive oxygen species and reactive nitrogen species, levels of stress-associated signaling molecules, and proinflammatory cytokines could be used to confirm the disease at an earlier stage. These biomarkers may also help to diagnose mutant based environment specific alterations in JEV genotypes causing high pathogenesis and have immense future applications in diagnostics. There is an utmost need for the development of new more authentic, appropriate, and reliable physiological, immunological, biochemical, biophysical, molecular, and therapeutic biomarkers to confirm the disease well in time to start the clinical aid to the patients. Hence, the present review aims to discuss new emerging biomarkers that could facilitate more authentic and fast diagnosis of JE disease and its related disorders in the future.

Medical entomology--back to the future?

Some of problems and challenges facing Medical/Veterinary Entomology are presented from my perspective, focusing on the current millennium. Topics include anthropogenic environmental changes created by population growth, administrative problems hindering science's response to these changes, and some of the scientific discoveries potentially providing solutions. As the title implies, many recent research discoveries have yet to be translated into major changes in control approaches for the major vectorborne public health problems, thereby providing an interesting mix of modern surveillance technology used to track problems and direct historical intervention solutions.

Emerging viral infections

PURPOSE OF REVIEW

This review highlights research and development in the field of emerging viral causes of encephalitis over the past year.

RECENT FINDINGS

There is new evidence for the presence of henipaviruses in African bats. There have also been promising advances in vaccine and neutralizing antibody research against Hendra and Nipah viruses. West Nile virus continues to cause large outbreaks in the United States, and long-term sequelae of the virus are increasingly appreciated. There is exciting new research regarding the variable susceptibility of different brain regions to neurotropic virus infection. Another cluster of solid organ transplant recipients developed encephalitis from organ donor-acquired lymphocytic choriomeningitis virus. The global epidemiology of Japanese encephalitis virus has been further clarified. Evidence continues to accumulate for the central nervous system involvement of dengue virus, and the recent deadly outbreak of enterovirus 71 in Cambodian children is discussed.

SUMMARY

In response to complex ecological and societal dynamics, the worldwide epidemiology of viral encephalitis continues to evolve in surprising ways. The articles highlighted here include new research on virus epidemiology and spread, new outbreaks as well as progress in the development of vaccines and therapeutics.

Using network analysis to explore if professional opinions on Japanese encephalitis risk factors in Nepal reflect a socio-ecological system perspective

Japanese encephalitis (JE) is the leading cause of viral encephalitis in Asia and a significant public health problem in Nepal. Its epidemiology is influenced by factors affecting its amplifying hosts (pigs), vectors (mosquitoes), and dead-end hosts (including people). While most control efforts target reduced susceptibility to infection either by vaccination of people or pigs or by reduced exposure to mosquitoes; the economic reality of Nepal makes it challenging to implement standard JE control measures. An ecohealth approach has been nominated as a way to assist in finding and prioritizing locally relevant strategies for JE control that may be viable, feasible, and acceptable. We sought to understand if Nepalese experts responsible for JE management conceived of its epidemiology in terms of a socio-ecological system to determine if they would consider ecohealth approaches. Network analysis suggested that they did not conceive JE risk as a product of a socio-ecological system. Traditional proximal risk factors of pigs, mosquitoes, and vaccination predominated experts' conception of JE risk. People seeking to encourage an ecohealth approach or social change models to JE management in Nepal may benefit from adopting social marketing concepts to encourage and empower local experts to examine JE from a socio-ecological perspective.

Japanese encephalitis: the virus and vaccines

Japanese encephalitis (JE) is an infectious disease of the central nervous system caused by Japanese encephalitis virus (JEV), a zoonotic mosquito-borne flavivirus. JEV is prevalent in much of Asia and the Western Pacific, with over 4 billion people living at risk of infection. In the absence of antiviral intervention, vaccination is the only strategy to develop long-term sustainable protection against JEV infection. Over the past half-century, a mouse brain-derived inactivated vaccine has been used internationally for active immunization. To date, however, JEV is still a clinically important, emerging, and re-emerging human pathogen of global significance. In recent years, production of the mouse brain-derived vaccine has been discontinued, but 3 new cell culture-derived vaccines are available in various parts of the world. Here we review current aspects of JEV biology, summarize the 4 types of JEV vaccine, and discuss the potential of an infectious JEV cDNA technology for future vaccine development.

Southernmost Asia is the source of Japanese encephalitis virus (genotype 1) diversity from which the viruses disperse and evolve throughout Asia

BACKGROUND

Although a previous study predicted that Japanese encephalitis virus (JEV) originated in the Malaysia/Indonesia region, the virus is known to circulate mainly on the Asian continent. However, there are no reported systematic studies that adequately define how JEV then dispersed throughout Asia.

METHODOLOGY/PRINCIPAL FINDINGS

In order to understand the mode of JEV dispersal throughout the entire Asian continent and the factors that determine the dispersal characteristics of JEV, a phylogenetic analysis using Bayesian Markov chain Monte Carlo simulations was conducted on all available JEV E gene sequences in GenBank, plus strains recently isolated in China. Here we demonstrate for the first time that JEV lineages can be divided into four endemic cycles, comprising southern Asia, eastern coastal Asia, western Asia, and central Asia. The isolation places of the viruses in each endemic cycle were geographically independent regardless of years, vectors, and hosts of isolation. Following further analysis, we propose that the southernmost region (Thailand, Vietnam, and Yunnan Province, China) was the source of JEV transmission to the Asian continent following its emergence. Three independent transmission routes from the south to north appear to define subsequent dispersal of JEV. Analysis of JEV population dynamics further supports these concepts.

CONCLUSIONS/SIGNIFICANCE

These results and their interpretation provide new insights into our understanding of JEV evolution and dispersal and highlight its potential for introduction into non-endemic areas.

Molecular phylogenetic and positive selection analysis of Japanese encephalitis virus strains isolated from pigs in China

Japanese encephalitis virus (JEV) is one of the most important virus which causes encephalitis. This disease is most prevalent in the south, southeast and the east region of Asia. In this study, two JEV strains, named JEV/SW/GD/01/2009 and JEV/SW/GZ/09/2004, were isolated from aborted fetuses and seminal fluid of pigs in China. To determine the characteristic of these virus isolates, the virulence of two newly JEV isolates was investigated, the result evidenced that the JEV/SW/GD/01/2009 did not kill mice, while the JEV/SW/GZ/09/2004 displayed neurovirulence with 0.925log10 p.f.u./LD50. Additionally, the full genome sequences of JEV were determined and compared with other known JEV strains. Results demonstrated that the genome of two JEV isolates was 10,976 nucleotides (nt) in length. As compared to the Chinese vaccine strain SA14-14-2, the JEV/SW/GD/01/2009 and the JEV/SW/GZ/09/2004 showed 99.7% and 97.5% identity at the nucleotide level, 99.6% and 96.7% identity at the amino acid level, respectively. Phylogenetic analysis, based on the full-length genome revealed that two JEV isolates were all clustered into genotype III compared to the reference strains. Furthermore, selection analyses revealed that dominant selective pressure acting on the JEV genome was purifying selection. Four sites under positive selection were identified: codon 521 (amino acid E-227), 2296 (amino acid NS4b-24), 3048 (amino acid NS5-521) and 3055 (amino acid NS5-528). Amino acid E-227 was proved to be related to neurovirulence. Taken together, the molecular epidemiology and functional of positively selected amino acid sites of two newly JEV isolates were fully understood, which might be helpful to predict possible changes in virulence.

Review of climate, landscape, and viral genetics as drivers of the Japanese encephalitis virus ecology

The Japanese encephalitis virus (JEV), an arthropod-born Flavivirus, is the major cause of viral encephalitis, responsible for 10,000–15,000 deaths each year, yet is a neglected tropical disease. Since the JEV distribution area has been large and continuously extending toward new Asian and Australasian regions, it is considered an emerging and reemerging pathogen. Despite large effective immunization campaigns, Japanese encephalitis remains a disease of global health concern. JEV zoonotic transmission cycles may be either wild or domestic: the first involves wading birds as wild amplifying hosts; the second involves pigs as the main domestic amplifying hosts. Culex mosquito species, especially Cx. tritaeniorhynchus, are the main competent vectors. Although five JEV genotypes circulate, neither clear-cut genotype-phenotype relationship nor clear variations in genotype fitness to hosts or vectors have been identified. Instead, the molecular epidemiology appears highly dependent on vectors, hosts' biology, and on a set of environmental factors. At global scale, climate, land cover, and land use, otherwise strongly dependent on human activities, affect the abundance of JEV vectors, and of wild and domestic hosts. Chiefly, the increase of rice-cultivated surface, intensively used by wading birds, and of pig production in Asia has provided a high availability of resources to mosquito vectors, enhancing the JEV maintenance, amplification, and transmission. At fine scale, the characteristics (density, size, spatial arrangement) of three landscape elements (paddy fields, pig farms, human habitations) facilitate or impede movement of vectors, then determine how the JEV interacts with hosts and vectors and ultimately the infection risk to humans. If the JEV is introduced in a favorable landscape, either by live infected animals or by vectors, then the virus can emerge and become a major threat for human health. Multidisciplinary research is essential to shed light on the biological mechanisms involved in the emergence, spread, reemergence, and genotypic changes of JEV.

Japanese encephalitis virus infects porcine kidney epithelial PK15 cells via clathrin- and cholesterol-dependent endocytosis

BACKGROUND

Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus that causes acute viral encephalitis in humans. Pigs are important amplifiers of JEV. The entry mechanism of JEV into porcine cells remains largely unknown. In this study, we present a study of the internalization mechanism of JEV in porcine kidney epithelial PK15 cells.

RESULTS

We demonstrated that the disruption of the lipid raft by cholesterol depletion with methyl-β-cyclodextrin (MβCD) reduced JEV infection. We also found that the knockdown of clathrin by small interfering RNA (siRNA) significantly reduced JEV-infected cells and JEV E-glycoprotein levels, suggesting that JEV utilizes clathrin-dependent endocytosis. In contrast, the knockdown of caveolin-1, a principal component of caveolae, had only a small (although statistically significant) effect on JEV infection, however, JEV entry was not affected by genistein. These results suggested that JEV entry was independent of caveolae.

CONCLUSIONS

Taken together, our results demonstrate that JEV enters porcine kidney epithelial PK15 cells through cholesterol- and clathrin-mediated endocytosis.

The effect of vaccination coverage and climate on Japanese encephalitis in Sarawak, Malaysia

BACKGROUND

Japanese encephalitis (JE) is the leading cause of viral encephalitis across Asia with approximately 70,000 cases a year and 10,000 to 15,000 deaths. Because JE incidence varies widely over time, partly due to inter-annual climate variability effects on mosquito vector abundance, it becomes more complex to assess the effects of a vaccination programme since more or less climatically favourable years could also contribute to a change in incidence post-vaccination. Therefore, the objective of this study was to quantify vaccination effect on confirmed Japanese encephalitis (JE) cases in Sarawak, Malaysia after controlling for climate variability to better understand temporal dynamics of JE virus transmission and control.

METHODOLOGY/PRINCIPAL FINDINGS

Monthly data on serologically confirmed JE cases were acquired from Sibu Hospital in Sarawak from 1997 to 2006. JE vaccine coverage (non-vaccine years vs. vaccine years) and meteorological predictor variables, including temperature, rainfall and the Southern Oscillation index (SOI) were tested for their association with JE cases using Poisson time series analysis and controlling for seasonality and long-term trend. Over the 10-years surveillance period, 133 confirmed JE cases were identified. There was an estimated 61% reduction in JE risk after the introduction of vaccination, when no account is taken of the effects of climate. This reduction is only approximately 45% when the effects of inter-annual variability in climate are controlled for in the model. The Poisson model indicated that rainfall (lag 1-month), minimum temperature (lag 6-months) and SOI (lag 6-months) were positively associated with JE cases.

CONCLUSIONS/SIGNIFICANCE

This study provides the first improved estimate of JE reduction through vaccination by taking account of climate inter-annual variability. Our analysis confirms that vaccination has substantially reduced JE risk in Sarawak but this benefit may be overestimated if climate effects are ignored.

TNF-α acts as an immunoregulator in the mouse brain by reducing the incidence of severe disease following Japanese encephalitis virus infection

Japanese encephalitis virus (JEV) causes acute central nervous system (CNS) disease in humans, in whom the clinical symptoms vary from febrile illness to meningitis and encephalitis. However, the mechanism of severe encephalitis has not been fully elucidated. In this study, using a mouse model, we investigated the pathogenetic mechanisms that correlate with fatal JEV infection. Following extraneural infection with the JaOArS982 strain of JEV, infected mice exhibited clinical signs ranging from mild to fatal outcome. Comparison of the pathogenetic response between severe and mild cases of JaOArS982-infected mice revealed increased levels of TNF-α in the brains of severe cases. However, unexpectedly, the mortality rate of TNF-α KO mice was significantly increased compared with that of WT mice, indicating that TNF-α plays a protective role against fatal infection. Interestingly, there were no significant differences of viral load in the CNS between WT and TNF-α KO mice. However, exaggerated inflammatory responses were observed in the CNS of TNF-α KO mice. Although these observations were also obtained in IL-10 KO mice, the mortality and enhanced inflammatory responses were more pronounced in TNF-α KO mice. Our findings therefore provide the first evidence that TNF-α has an immunoregulatory effect on pro-inflammatory cytokines in the CNS during JEV infection and consequently protects the animals from fatal disease. Thus, we propose that the increased level of TNF-α in severe cases was the result of severe disease, and secondly that immunopathological effects contribute to severe neuronal degeneration resulting in fatal disease. In future, further elucidation of the immunoregulatory mechanism of TNF-α will be an important priority to enable the development of effective treatment strategies for Japanese encephalitis.

Temporal changes of Japanese encephalitits virus in different brain regions of rat

BACKGROUND & OBJECTIVES

Japanese encephalitis virus (JEV) infection results in acute encephalitic illness. The affinity of JEV to different regions of brain and temporal changes in viral load have not been studied. This study was conducted to describe localization of JEV to different regions of the brain at different stages of disease in a rat model of Japanese encephalitis (JE).

METHODS

Twelve days old Wistar rats were inoculated intracerebrally with a dose of 3 x 10⁶ pfu/ml of JEV. After 3, 6, 10 and 20 days post-inoculation, brains were dissected out and different regions of brain (cortex, striatum, thalamus and mid brain) were taken. Motor deficit was assessed by the rota rod and JEV RNA copies were evaluated using real-time PCR assay.

RESULTS

There was a significant increase in motor deficit in rats inoculated with JEV compared to the controls. JEV RNA copies were present in all studied regions of the brain on days 3, 6 and 10 post-inoculation. Maximum number of JEV RNA copies were present in the mid brain on days 3 and 10 post-inoculation. JEV RNA copies were not detected in any of the brain regions on day 20.

INTERPRETATION & CONCLUSIONS

This study reports JEV RNA load in different brain regions of rat with higher affinity of JEV virus to thalamus and mid brain compared to other regions.

Japanese Encephalitis Virus Generated Neurovirulence, Antigenicity, and Host Immune Responses

In response to a JE virus attack, infected body cells start secretion of different cytokines and activate innate immune response. Virus starts neuronal invasion by entering into nerve cells and inflecting the central nervous system. It avoids exposure of body’s natural immunity and generates neurotrophic effects. Virus causes acute susceptibility to CNS and establishes encephalitis syndrome that results in very high fatality in children. In survivors, JEV inhibits the growth and proliferation of NCPs and imposes permanent neuronal disorders like cognitive, motor, and behavioral impairments. However, body cells start TCR mediated interactions, to recognize viral antigens with class I MHC complex on specific target cells, and operate mass killing of virus infected cells by increased CTL activity. Thus, both cell mediated and antibody interactions plays a central role in protection against JEV. In the present review article virus generated neurovirulence, antigenicity, and host immune responses are described in detail. More emphasis is given on diagnosis, clinical care, and active immunization with well-designed potential antiflavivirus vaccines. Further, for achieving an elite success against JEV, global eradication strategies are to be needed for making vaccination program more responsible and effective in endemic areas.

Comparison of genomic and amino acid sequences of eight Japanese encephalitis virus isolates from bats

We compared nucleotide and deduced amino acid sequences of eight Japanese encephalitis virus (JEV) isolates derived from bats in China. We also compared the bat JEV isolates with other JEV isolates available from GenBank to determine their genetic similarity. We found a high genetic homogeneity among the bat JEVs isolated in different geographical areas from various bat species at different time periods. All eight bat JEV isolates belonged to genotype III. The mean evolutionary rate of bat JEV isolates was lower than those of isolates of other origin, but this difference was not statistically significant. Based on these results, we presume that the bat JEV isolates might be evolutionarily conserved. The eight bat JEV isolates were phylogenetically similar to mosquito BN19 and human Liyujie isolates of JEV. These results indicate that bats might be involved in natural cycle of JEV.

Spatiotemporal patterns of Japanese encephalitis in China, 2002-2010

Objective

The aim of the study is to examine the spatiotemporal pattern of Japanese Encephalitis (JE) in mainland China during 2002–2010. Specific objectives of the study were to quantify the temporal variation in incidence of JE cases, to determine if clustering of JE cases exists, to detect high risk spatiotemporal clusters of JE cases and to provide evidence-based preventive suggestions to relevant stakeholders.

Methods

Monthly JE cases at the county level in mainland China during 2002–2010 were obtained from the China Information System for Diseases Control and Prevention (CISDCP). For the purpose of the analysis, JE case counts for nine years were aggregated into four temporal periods (2002; 2003–2005; 2006; and 2007–2010). Local Indicators of Spatial Association and spatial scan statistics were performed to detect and evaluate local high risk space-time clusters.

Results

JE incidence showed a decreasing trend from 2002 to 2005 but peaked in 2006, then fluctuated over the study period. Spatial cluster analysis detected high value clusters, mainly located in Southwestern China. Similarly, we identified a primary spatiotemporal cluster of JE in Southwestern China between July and August, with the geographical range of JE transmission increasing over the past years.

Conclusion

JE in China is geographically clustered and its spatial extent dynamically changed during the last nine years in mainland China. This indicates that risk factors for JE infection are likely to be spatially heterogeneous. The results may assist national and local health authorities in the development/refinement of a better preventive strategy and increase the effectiveness of public health interventions against JE transmission.

Japanese encephalitis (JE) is a mosquito-borne disease, which primarily occurs in rural and suburban areas of Southeast Asia and the Western Pacific region. JE still remains a significant public health problem in mainland China, with approximately 50% of global cases annually. Few studies have explored the spatiotemporal patterns of JE cases in China. Here we reported the results of Local Indicators of Spatial Association and spatial scan statistics of JE cases in mainland China at the county level during the four periods: 2002; 2003–2005; 2006; 2007–2010. The primary spatiotemporal cluster of JE was detected in Southwestern China between July and August, with the geographical range of JE transmission increasing over the past years. The results of LISA and spatial scan statistics were consistent which indicates that these methods are reliable and could have wider applications in the fields of disease surveillance and management in China, particularly in the surveillance and monitoring of other vector-borne diseases. These findings may assist in informing prevention and control strategies and increase the effectiveness of public health interventions against JE transmission.

Circulation of Japanese encephalitis virus in pigs and mosquito vectors within Can Tho city, Vietnam

Japanese encephalitis virus (JEV) is a mosquito-borne, zoonotic flavivirus causing encephalitis in humans and reproductive disorder in pigs. JEV is present in large parts of Asia, where urbanization is high. Households within and outside Can Tho city, South Vietnam, were selected to monitor circulation of JEV. A nested RT-PCR was established to detect the presence of JEV in mosquitoes whereas sera from pigs belonging to households within the province were analyzed for the presence of antibodies to JEV. A total of 7885 mosquitoes were collected and divided into 352 pools whereof seven were JEV-positive, six of which were collected within the city. Fragments from four pools clustered with JEV genotype III and three with genotype I. Of the 43 pigs sampled inside the city 100% had JEV antibodies. Our study demonstrates exposure to JEV in pigs, and co-circulation of JEV genotype I and III in mosquitoes within an urban environment in South Vietnam. Thus, although JEV has mainly been considered a rural disease, the potential for transmission in urban areas cannot be ignored.

Zoonoses in South-East Asia: a regional burden, a global threat

Zoonoses are an issue of growing interest in South-East Asia, where environmental factors and socio-economic context favor the endemization of well-known diseases and the emergence of new pathogens at the human-wildlife interface. However, the health status of the region with respect to many zoonotic diseases remains poorly defined, despite the high overall burden of zoonoses on the countries of the area, and the global risk of new biological threats in the region. The first objective of this paper was to provide an update of data on the zoonoses commonly described by the scientific community and reported by governmental institutions and international organizations in continental South-East Asia. The analysis of the available data led to the identification of some trends in the evolution of the diseases, as well as some gaps in knowledge and in the current surveillance and control networks. In light of these findings, we discuss measures for effectively addressing zoonotic disease issues in South-East Asia, such as the allocation of funds for research and for surveillance and control programs, and a multi-sectoral and multi-disciplinary approach at various levels.

Climate change and mosquito-borne diseases in China: a review

China has experienced noticeable changes in climate over the past 100 years and the potential impact climate change has on transmission of mosquito-borne infectious diseases poses a risk to Chinese populations. The aims of this paper are to summarize what is known about the impact of climate change on the incidence and prevalence of malaria, dengue fever and Japanese encephalitis in China and to provide important information and direction for adaptation policy making. Fifty-five papers met the inclusion criteria for this study. Examination of these studies indicates that variability in temperature, precipitation, wind, and extreme weather events is linked to transmission of mosquito-borne diseases in some regions of China. However, study findings are inconsistent across geographical locations and this requires strengthening current evidence for timely development of adaptive options. After synthesis of available information we make several key adaptation recommendations including: improving current surveillance and monitoring systems; concentrating adaptation strategies and policies on vulnerable communities; strengthening adaptive capacity of public health systems; developing multidisciplinary approaches sustained by an new mechanism of inter-sectional coordination; and increasing awareness and mobilization of the general public.

Development and characterization of the replicon system of Japanese encephalitis live vaccine virus SA14-14-2

Background

Viral self-replicating sub-genomic replicons represent a powerful tool for studying viral genome replication, antiviral screening and chimeric vaccine development. Many kinds of flavivirus replicons have been developed with broad applications.

Findings

The replicon system of JEV live vaccine strain SA14-14-2 was successfully developed in this study. Two kinds of replicons that express enhanced green fluorescent protein (EGFP) and Renilla luciferase (R.luc) were constructed under the control of SP6 promoter, respectively. Robust EGFP and R.luc signals could be detected in the replicon-transfected BHK-21 cells. Furthermore, the potential effects of selected amino acids in the C-terminal of envelope protein on replication were characterized using the replicon system.

Conclusions

Our results provide a useful platform not only for the study of JEV replication, but also for antiviral screening and chimeric vaccine development.

JE-ADVAX vaccine protection against Japanese encephalitis virus mediated by memory B cells in the absence of CD8(+) T cells and pre-exposure neutralizing antibody

JE-ADVAX is a new, delta inulin-adjuvanted, Japanese encephalitis (JE) candidate vaccine with a strong safety profile and potent immunogenicity that confers efficient immune protection not only against JE virus but also against related neurotropic flaviviruses such as West Nile virus. In this study, we investigated the immunological mechanism of protection by JE-ADVAX vaccine using knockout mice deficient in B cells or CD8(+) T cells and poor persistence of neutralizing antibody or by adoptive transfer of immune splenocyte subpopulations. We show that memory B cells induced by JE-ADVAX provide long-lived protection against JE even in the absence of detectable pre-exposure serum neutralizing antibodies and without the requirement of CD8(+) T cells. Upon virus encounter, these vaccine-induced memory B cells were rapidly triggered to produce neutralizing antibodies that then protected immunized mice from morbidity and mortality. The findings suggest that the extent of the B-cell memory compartment might be a better immunological correlate for clinical efficacy of JE vaccines than the currently recommended measure of serum neutralizing antibody. This may explain the paradox where JE protection is observed in some subjects even in the absence of detectable serum neutralizing antibody. Our investigation also established the suitability of a novel flavivirus challenge model (β(2)-microglobulin-knockout mice) for studies of the role of B-cell memory responses in vaccine protection.

Surveillance of Japanese encephalitis virus infection in mosquitoes in Vietnam from 2006 to 2008

Japanese encephalitis virus (JEV) infection in mosquitoes was monitored in Vietnam from 2006 to 2008. A total of 15,225 mosquitoes, identified as 26 species in five genera were collected and 12,621 were grouped into 447 pools for examination of JEV infection by assays for cytopathic effects in C6/36 cells and by RT-PCR to detect flavivirus RNA. Three JEV strains were isolated from Culex tritaeniorhynchus Giles collected in northern and southern Vietnam and two JEV strains were isolated from Culex vishnui Theobald collected in the highlands of Vietnam. Genetic and phylogenetic analyses, based on complete E gene nucleotide sequences, revealed that the five JEV strains were classified into the genotype I group and six amino acid differences were found in these five strains. These results indicated that multiple JEV genotype I populations are circulating countrywide in Vietnam, transmitted by bites of their Cx. tritaeniorhynchus and Cx. vishnui.

Insecticide susceptibility of field-collected populations of Culex tritaeniorhynchus in the Republic of Korea

The toxicities of 10 insecticides were examined against late third instar Culex tritaeniorhynchus Giles (Diptera: Culicidae) using the direct-contact mortality bioassay. Six geospatially-distant field mosquitoes were collected from Chuncheon-si, Hwaseong, Seosan. Jeonju, Daegu, and Busan in the Republic of Korea. Marked regional variations of insecticide susceptibility were observed. Field populations of Seosan, Jeonju, and Daegu from agricultural areas showed higher to extremely higher insecticide susceptibility to pyrethroids than those of Chuncheon-si, Hwaseong, and Busan strains from non-agricultural areas. Extremely high to low levels of susceptibility were measured: bifenthrin, susceptible ratio (SR) = 2.7-896.3; β-cyfluthrin, SR = 1.8-633.3; α-cypermethrin, SR = 1.2-1,051.9; deltamethrin, SR = 1.3-711.1; permethrin, SR = 1.5-1,053.4; etofenprox, SR = 2.2-29.3; chlorfenapyr, SR = 5.1-103.6; chlorpyrifos, SR = 2.3- 337.0; fenitrothion, SR = 2.0-142.3; and fenthion, SR = 1.4-186.2. Cx. tritaeniorhynchus populations from rice paddies had been under heavy selection pressure due to the agricultural insecticides, and that's why the mosquito species demonstrated high resistance to pyrethroids, which were used for a long time to control agricultural pests in the localities. These results indicate that careful selection and rotational use of these insecticides may result in continued satisfactory control against field populations of Japanese encephalitis vector mosquitoes.

Japanese encephalitis: on the One Health agenda

Japanese encephalitis (JE) is one of the most well studied arthropod zoonotic diseases with human and animal research and their integration spanning 6-7 decades. JE research and policy in some Asian countries has epitomized the 'One Health' strategy of attainment of optimal health for people, animals, and the environment. However, despite significant mitigation of JE in some Asian countries primarily due to vaccination programs and infrastructural development, JE continues to be a major disease burden in the Asian region. Arthropod-borne zoonotic infections such as JE present some of the greatest challenges to animal and human health globally. Their emergence involves a complex interplay of vectors, hosts, environment, climate, and anthropogenic factors. Therefore, the integrated management of infectious agents that affect both humans and animals is perhaps the most highly coveted strategy that public health policy makers aspire to attain in the twenty-first century. This is in response to the seemingly growing challenges of controlling the burden of emerging infectious diseases such as shrinking financial budgets and resources, increasing demand for public health deliverables, demographic shifts and mobility, global trade economies, and climate and landscape changes. Thus, while JE research and policy is an excellent example of the One Health strategy in action, further work is required to address the obstinate burden of transmission.

Occurrence of Japanese encephalitis virus mosquito vectors in relation to urban pig holdings

Japanese encephalitis virus (JEV) is transmitted to humans from pigs or birds by mosquitoes. In this study, the association between urban pig keeping and mosquito vectors was analyzed. A total of 7, 419 mosquitoes were collected overnight in urban households with and without pigs in Can Tho City, Vietnam. The most prevalent vectors were Culex tritaeniorhynchus (36%), Cx. gelidus (24%), and Cx. quinquefasciatus (15%), which were present in all parts of the city. Pigs were associated with increased numbers of Cx. tritaeniorhynchus. Traps close to pigs had higher numbers of Cx. tritaeniorhynchus and Cx. gelidus than traps close to humans. Increased number of persons in the household was associated with increased numbers of Cx. quinquefasciatus. We demonstrate that JEV vector species are present at urban households with and without pigs, and show that keeping pigs in an urban area increase the number of mosquitoes competent as vectors for JEV.