Meta-analyses of the proportion of Japanese encephalitis virus infection in vectors and vertebrate hosts

Revisiting the risk of introduction of Japanese encephalitis virus (JEV) into the United States - An updated semi-quantitative risk assessment

Japanese encephalitis virus (JEV) is associated with encephalitis in humans and reproductive and neurological illness in pigs. JEV has expanded beyond its native distribution in southeast Asia, with identifications in Europe (2010) and Africa (2016), and most recently, its spread into mainland Australia (2021-2022). The introduction of JEV into the United States (US) is a public health risk, and could also impact animal health and the food supply. To efficiently and cost-effectively manage risk, a better understanding of how and where diseases will be introduced, transmitted, and spread is required. To achieve this objective, we updated our group's previous qualitative risk assessment using an established semi-quantitative risk assessment tool (MINTRISK) to compare the overall rate of introduction and risk, including impacts, of JEV in seven US regions. The rate of introduction from the current region of distribution was considered negligible for the Northeast, Midwest, Rocky Mountain, West, Alaska, and Hawaii regions. The South region was the only region with a pathway that had a non-negligible rate of introduction; infected mosquito eggs and larvae introduced via imported used tires (very low; 95% uncertainty interval (UI) = negligible to high). The overall risk estimate for the South was very high (95% UI = very low to very high). Based on this risk assessment, the South region should be prioritized for surveillance activities to ensure the early detection of JEV. The assumptions used in this risk assessment, due to the lack of information about the global movement of mosquitoes, number of feral pigs in the US, the role of non-ardeid wild birds in transmission, and the magnitude of the basic reproduction ratio of JEV in a novel region, need to be fully considered as these impact the estimated probability of establishment.

Prevalence of dengue, Zika, and chikungunya virus infections among mosquitoes in Asia: A systematic review and meta-analysis

BACKGROUND

Dengue virus (DENV), Zika virus (ZIKV), and chikungunya virus (CHIKV) continue to pose significant public health risks. This study aims to assess the prevalence of these arbovirus infections in field-caught mosquitoes across Asia.

METHODS

Studies published after the year 2000 on DENV, ZIKV, and/or CHIKV infections in Asian mosquitoes were identified from Embase, Scopus, PubMed, and Ovid. A random-effects model estimated the pooled prevalence, defined as the overall prevalence from included studies, adjusted for variability among the studies. Meta-regression models were used to evaluate the association between predictors and their prevalence.

RESULTS

A total of 2529 articles were retrieved; 57 met the inclusion criteria. Pooled prevalence of DENV, ZIKV, and CHIKV infections in Asian mosquitoes were 5.85%, 2.15%, and 1.26%, respectively. Subgroup analysis revealed varying DENV prevalence across regions: East Asia (3.32%), South Asia (5.26%), and Southeast Asia (6.92%). Univariate regression analysis demonstrated significant associations between mosquito capture site and DENV prevalence (P < 0.001), and between study region and ZIKV prevalence (P = 0.005). However, no significant predictors were identified for CHIKV prevalence.

CONCLUSION

Our findings provide reference pooled summary estimates of arbovirus infections in mosquitoes, offering crucial insight into the regional disease burden and - guidance in the development and implementation of arbovirus surveillance in mosquitoes.

Study on the temporal and spatial distribution of Culex mosquitoes in Hanoi, Vietnam

Arboviruses transmitted by mosquitoes, including Japanese encephalitis virus (JEV), present a substantial global health threat. JEV is transmitted by mosquitoes in the genus Culex, which are common in both urban and rural areas in Vietnam. In 2020, we conducted a 1-year survey of Culex mosquito abundance in urban, suburban, and peri-urban areas of Hanoi using CDC-light traps. Mosquitoes were identified to species and sorted into pools based on species, sex, and trap location. The mosquito pools were also investigated by RT-qPCR for detection of JEV. In total, 4829 mosquitoes were collected over a total of 455 trap-nights, across 13 months. Collected mosquitoes included Culex, Aedes, Anopheles, and Mansonia species. Culex mosquitoes, primarily Cx. quinquefasciatus, predominated, especially in peri-urban areas. Most Culex mosquitoes were caught in the early months of the year. The distribution and abundance of mosquitoes exhibited variations across urban, suburban, and peri-urban sites, emphasizing the influence of environmental factors such as degree of urbanization, temperature and humidity on Culex abundance. No JEV was detected in the mosquito pools. This study establishes baseline knowledge of Culex abundance and temporal variation, which is crucial for understanding the potential for JEV transmission in Hanoi.

First molecular evidence of potential Culicoides vectors implicated in bluetongue virus transmission in Morocco

BACKGROUND

Bluetongue is a non-contagious viral disease that affects both domestic and wild ruminants. It is transmitted primarily by small hematophagous Diptera belonging to the genus Culicoides (Diptera: Ceratopogonidae). The current study represents the first molecular investigation into the potential role of Culicoides imicola, Culicoides paolae, Culicoides newsteadi, Culicoides spp., and Culicoides circumscriptus as bluetongue virus (BTV) vectors in Morocco. Additionally, the study aimed to evaluate the vectorial activity of midges during the survey seasons.

METHODS

Parous females of these species were captured from several regions of Morocco (6 out of 12) from 2018 to 2021 using Onderstepoort Veterinary Institute (OVI) traps. A total of 2003 parous female specimens were grouped into 55 batches. The midge body of each batch was dissected into three regions (head, thorax, and abdomen), and these regions were analyzed separately using reverse transcription quantitative polymerase chain reaction (RT-qPCR).

RESULTS

BTV RNA was detected in 45 out of the 55 batches tested, indicating a positivity rate of 81.8%. The RT-qPCR-positive pools of the studied Culicoides species exhibited high levels of BTV positivity in each body part (head, thorax, and abdomen), confirming the successful replication of the virus within midge bodies. The BTV circulation was substantial across all three survey seasons (spring, summer, and autumn). High infection rates, calculated using the minimum infection rate (MIR) and maximum likelihood estimation (MLE), were observed during the collection seasons, particularly in autumn and spring, and for all investigated Culicoides species, most notably for C. imicola and C. newsteadi. These increased infection rates underscore the significant risk of Culicoides transmitting the BTV in Morocco.

CONCLUSIONS

The detection of BTV positivity in Culicoides spp. (lacking wing spots that allow their differentiation according to morphological identification keys) suggested that other Culicoides species are competent for BTV transmission in Morocco. The study results indicated, for the first time at the molecular level, that C. imicola and C. newsteadi are the primary potential vectors of BTV in Morocco and that C. paolae and C. circumscriptus are strongly implicated in the propagation of bluetongue at the national level.

Phylogeny and spatial distribution of Japanese encephalitis virus vector species in Cambodia

In Southeast Asia, despite the use of Japanese encephalitis vaccines and vaccination coverage, Japanese encephalitis (JE) transmission is still a major public health issue. The main vectors of this virus are mosquitoes from the genus Culex, which diversity and density are important in Southeast Asia. The main vector species of Japanese encephalitis virus (JEV) in Cambodia belong to the Vishnui subgroup. However, their morphological identification solely based on the adult stage remains challenging, making their segregation and detection difficult. In order to identify and describe the distribution of the three main JEV vector species in Cambodia, namely Culex vishnui, Cx. pseudovishnui and Cx. tritaeniorhynchus, mosquito samplings were carried out throughout the country in different environments. Phylogenetic analysis of the cytochrome c oxidase subunit I (coI) gene using maximum-likelihood tree with ultrafast bootstrap and phylogeographic analysis were performed. The three main Culex species are phylogenetically separated, and represent two distinct clades, one with Cx. tritaeniorhynchus and the second with Cx. vishnui and Cx. pseudovishnui, the latter appearing as a subgroup of Cx. vishnui. The phylogeographic analysis shows a distribution of the Vishnui subgroup on the entire Cambodian territory with an overlapped distribution areas leading to a sympatric distribution of these species. The three JEV vector species are geographically well-defined with a strong presence of Cx. pseudovishnui in the forest. Combined with the presence of Cx. tritaeniorhynchus and Cx. vishnui in rural, peri-urban, and urban areas, the presence of JEV-competent vectors is widespread in Cambodia.

Epidemiology and risk factors of Japanese encephalitis in Taiwan, 2010-2022

INTRODUCTION

Taiwan introduced a two-dose inactivated Japanese encephalitis (JE) mouse brain-derived (JE-MB) vaccine into routine childhood immunization in 1968, with booster vaccination implemented in 1974 and 1983. In 2017, JE-MB vaccine was replaced by a two-dose live-attenuated chimeric vaccine (JE-CV). After implementation of JE vaccination programs, JE cases have shifted from children to adults. In this study, we described the JE epidemiology and identify high-risk groups to further inform vaccine policy.

METHODOLOGY/PRINCIPAL FINDINGS

We extracted data from Taiwan's notifiable disease surveillance database, vital statistics, and employment statistics from 2010 to 2022. Diagnosis of JE was confirmed by JE seroconversion, a four-fold increase in virus-specific antibodies, a positive JE viral nucleic-acid test, or JE virus isolation. From 2010 to 2022, a total of 313 cases of JE were diagnosed, resulting in an overall incidence rate of 0.10 cases per 100,000 person-years and a mortality rate of 0.006 per 100,000 population per year. Among these patients, 64% were male, and the median age was 51 years (range 0-82). Compared with people born in or after 1976 (vaccinated with four doses of JE-MB vaccine or two doses of JE-CV), those born in or before 1962 (unvaccinated) and those born during 1963-1975 (vaccinated with two or three doses of JE-MB vaccine) had a 4.2-fold (95% confidence interval [CI] 3.0-5.7) and 5.9-fold (95% CI 4.3-8.1) higher risk of JE, respectively. The relative risk of working in agriculture, forestry, fishing, or animal husbandry, compared to other occupations, was 5.0 (95% CI 3.5-7.0).

CONCLUSIONS/SIGNIFICANCE

In Taiwan, individuals born before 1976 and those employed in agriculture, forestry, fishing, or animal husbandry had a higher risk of JE. We recommend JE vaccination for people in these high-risk groups who have not been fully vaccinated or have an unknown vaccination history.

Prevalence of Japanese encephalitis (JE) virus in mosquitoes and animals of the Asian continent: A systematic review and meta-analysis

BACKGROUND

Japanese encephalitis (JE) is a viral zoonotic disease that has been found in several countries of Asia and is responsible for high mortality and morbidity of men and animals in rural and sub-urban endemic areas due to the virus re-circulation among diverse hosts and vectors. The present study estimates the prevalence of the JE virus in the vector and animal population of the Asian continent using a systematic review and meta-analysis.

METHODS

The Cochran collaborators' Preferred Reporting Items for Systematic Reviews and Meta-Analysis [PRISMA] guidelines were used for systematic review and meta-analysis. The heterogeneity was observed in meta-regression analysis due to several factors including region, species, and different diagnostic assays used in various studies. Thus we did sensitivity and subgroup analysis.

RESULTS

The prevalence of the JE virus was calculated using a total sample size of 47,391. Subgroup analysis revealed the JE virus prevalence of 39% in the Southeast Asia region, followed by East Asia with 35% and South Asia with 15% prevalence. Hence, the overall pooled prevalence of the JE virus was 26% in the Asian continent.

CONCLUSIONS

The highest proportion of infection was found in pigs amongst all animals, reinforcing the fact that they can be used as sentinels to predict outbreaks in humans. The findings of this study will enable researchers and policymakers in better understanding the disease's spatial and temporal distribution, as well as in creating and implementing location-specific JE prevention and control measures.

Environmental factors and spatiotemporal distribution of Japanese encephalitis after vaccination campaign in Guizhou Province, China (2004-2016)

Background

Although a vaccination campaign has been conducted since 2004, Japanese encephalitis (JE) is still a public health problem in Guizhou, one of the provinces with the highest incidence of JE in China. The aim of this study was to understand the spatiotemporal distribution of JE and its relationship with environmental factors in Guizhou Province in the post-vaccination era, 2004–2016.

Methods

We collected data on human JE cases in Guizhou Province from 2004 to 2016 from the national infectious disease reporting system. A Poisson regression model was used to analyze the relationship between JE occurrence and environmental factors amongst counties.

Results

Our results showed that the incidence and mortality of JE decreased after the initiation of vaccination. JE cases were mainly concentrated in preschool and school-age children and the number of cases in children over age 15 years was significantly decreased compared with the previous 10 years; the seasonality of JE before and after the use of vaccines was unchanged. JE incidence was positively associated with cultivated land and negatively associated with gross domestic product (GDP) per capita, vegetation coverage, and developed land. In areas with cultivated land coverage < 25%, vegetation coverage > 55%, and urban area coverage > 25%, the JE risk was lower. The highest JE incidence was among mid-level GDP areas and in moderately urbanized areas.

Conclusions

This study assessed the relationship between incidence of JE and environmental factors in Guizhou Province. Our results highlight that the highest risk of JE transmission in the post-vaccination era is in mid-level developed areas.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12879-021-06857-3.

Metagenomic analysis reveals Culex mosquito virome diversity and Japanese encephalitis genotype V in the Republic of Korea

Recent outbreaks of emerging and re-emerging viruses have shown that timely detection of novel arboviruses with epidemic potential is essential to mitigate human health risks. There are rising concerns that emergent JEV genotype V (GV) is circulating in Asia, against which current vaccines may not be efficacious. To ascertain if JEV GV and other arboviruses are circulating in East Asia, we conducted next-generation sequencing on 260 pools of Culex tritaeniorhynchus and Culex bitaeniorhynchus mosquitoes (6540 specimens) collected at Camp Humphreys, Republic of Korea (ROK) in 2018. Interrogation of our data revealed a highly abundant and diverse virosphere that contained sequences from 122 distinct virus species. Our statistical and hierarchical analysis uncovered correlates of potential health, virological, and ecological relevance. Furthermore, we obtained evidence that JEV GV was circulating in Pyeongtaek and, retrospectively, in Seoul in 2016 and placed these findings within the context of human and fowl reservoir activity. Sequence-based analysis of JEV GV showed a divergent genotype that is the most distant from the GIII-derived live attenuated SA14-14-2 vaccine strain and indicated regions probably responsible for reduced antibody affinity. These results emphasize recent concerns of shifting JEV genotype in East Asia and highlight the critical need for a vaccine proven efficacious against this re-emergent virus. Together, our one-health approach to Culex viral metagenomics uncovered novel insights into virus ecology and human health.

Japanese encephalitis virus infection in meerkats (Suricata suricatta)

Japanese encephalitis virus (JEV) infection has been recognized as a serious disease in humans. Wildlife animal infections due to JEV have not been well described. This study identified JEV infection in two deceased meerkats in Thailand, with clinical signs of neurological disease. Histopathology of brains revealed severe lymphoplasmacytic necrotizing meningoencephalitis, while similar inflammation was observed in the lung and liver. Partial JEV sequences were identified from the formalin-fixed paraffin-embedded-derived brain sections of two meerkats and were found to be genetically similar to a JEV strain detected in China but not from a local strain. Using immunohistochemistry, the virus was identified in neurons and glial cells, and also found in bronchial glands, Kupffer's cells in liver, lymphocytes in the spleen and pancreatic acini, which suggests extraneural infection. Transmission electron microscopy confirmed the presence of spheroid viral particles in the lungs. These findings may suggest that infection of extraneural organs in meerkats is similar to that described in JEV-infected humans. In conclusion, this study identified the first JEV infection in meerkats as an interesting case study. The JEV should be considered as an important differential diagnosis in meerkats with encephalitis. Further surveillance on JEV infection in meerkats and other wildlife species in a large cohort is needed in the future study.

Mosquito Vector Competence for Japanese Encephalitis Virus

Japanese encephalitis virus (JEV) is a zoonotic pathogen mainly found in East and Southeast Asia and transmitted by mosquitoes. The objective of this review is to summarize the knowledge on the diversity of JEV mosquito vector species. Therefore, we systematically analyzed reports of JEV found in field-caught mosquitoes as well as experimental vector competence studies. Based on the investigated publications, we classified 14 species as confirmed vectors for JEV due to their documented experimental vector competence and evidence of JEV found in wild mosquitoes. Additionally, we identified 11 mosquito species, belonging to five genera, with an experimentally confirmed vector competence for JEV but lacking evidence on their JEV transmission capacity from field-caught mosquitoes. Our study highlights the diversity of confirmed and potential JEV vector species. We also emphasize the variety in the study design of vector competence investigations. To account for the diversity of the vector species and regional circumstances, JEV vector competence should be studied in the local context, using local mosquitoes with local virus strains under local climate conditions to achieve reliable data. In addition, harmonization of the design of vector competence experiments would lead to better comparable data, informing vector and disease control measures.

Conclusions

We are currently experiencing two pandemics, one caused by a coronavirus and one by the reemerging dengue flaviviruses. Strict protective measures have been taken to safeguard against this coronavirus, which may have saved many lives. Fear, depression, and suicide have also resulted from these measures. In addition to dengue, other flaviviruses of humans or animals may also rapidly spread and become more pathogenic, as have Zika and West Nile viruses. Many viruses may have originated in bats or rodents. Several bats are seropositive for dengue, Saint Louis encephalitis, and Japanese encephalitis viruses. Some rodents are seropositive for tickborne encephalitis, West Nile, Usutu, and Wesselsbron viruses. Domestic animals, especially cattle and sheep, but also dogs and cats, have a much higher incidence of flavivirus infection than bats and rodents and have closer contact with humans. Less-toxic, broad-spectrum antiviral agents that are active against these and other emerging flaviviruses are needed to protect against future viral threats.

Detection of Japanese encephalitis virus in mosquitoes from Xinjiang during next-generation sequencing arboviral surveillance

A total of 548 mosquitoes were collected from different animal farms located near to highly populated cities in Xinjiang and were subjected to metagenomic next-generation sequencing (mNGS). The mNGS data demonstrated that 18,842 (XJ1 strain) and 1,077 (XJ2 strain) of Japanese encephalitis virus (JEV)-related reads were detected in XJ1 and XJ2 mosquito samples collected from Wushi and Wensu counties of Aksu area, which accounted for 0.032% and 0.006% of the total clean reads generated from XJ1 and XJ2 samples, respectively. The Bayesian molecular phylogenetic analysis suggested that XJ1 and XJ2 strains belonged to JEV genotype III and were clustered with JEV strains isolated in China. Notably, Bayesian molecular time line phylogeny revealed that XJ1 strain shared its MRCA with JEV GSS strain about 67 YA, suggesting that XJ1 strain likely originated from linages closely related to GSS strain and spread to Xinjiang later. Overall, these findings suggest that Xinjiang was probably not free from JEV, and thus, a further surveillance of JEV is required in Xinjiang.

Perspectives Regarding the Risk of Introduction of the Japanese Encephalitis Virus (JEV) in the United States

Japanese encephalitis (JE) is a zoonotic, emerging disease transmitted by mosquito vectors infected with the Japanese encephalitis virus (JEV). Its potential for emergence into susceptible regions is high, including in the United States (US), and is a reason of economic concern among the agricultural community, and to public health due to high morbidity and mortality rates in humans. While exploring the complexities of interactions involved with viral transmission, we proposed a new outlook on the role of vectors, hosts and the environment under changing conditions. For instance, the role of feral pigs may have been underappreciated in our previous work, given research keeps pointing to the importance of susceptible populations of wild swine in naïve regions as key elements for the introduction of emergent vector-borne diseases. High risk of JEV introduction has been associated with the transportation of infected mosquitoes via aircraft. Nonetheless, no JEV outbreaks have been reported in the US to date and results from a qualitative risk assessment considered the risk of establishment to be negligible under the current conditions (environmental, vector, pathogen, and host). In this work, we discuss virus-vector-host interactions and ecological factors important for virus transmission and spread, review research on the risk of JEV introduction to the US considering the implications of risk dismissal as it relates to past experiences with similar arboviruses, and reflect on future directions, challenges, and implications of a JEV incursion.

Evaluation of Japanese encephalitis virus E and NS1 proteins immunogenicity using a recombinant Newcastle disease virus in mice

Japanese encephalitis (JE) is the most important cause of acute encephalitis syndrome (AES). Japanese encephalitis virus (JEV), the prototype member of the JE serocomplex, belongs to the genus Flavivirus. The immunogenic proteins envelope (E) and non-structural protein 1 (NS1) of JEV are widely explored for the development of vaccines and diagnostics against JEV. However, there are underlying concerns such as the risk of reversion of live-attenuated vaccines to high virulence, the incomplete inactivation of pathogens in inactivated vaccines and partial vaccine coverage. Newcastle disease virus (NDV) is an efficient viral vaccine vector to express several human and animal immunogenic proteins. In the present study, we have developed a recombinant NDV (rNDV), individually expressing the E and NS1 proteins of JEV (rNDV-Ejev and rNDV-NS1jev). The recovered rNDV-Ejev and rNDV-NS1jev were characterized in 9-day-old SPF embryonated chicken eggs and in cell culture. The vaccination of rNDV-Ejev and rNDV-NS1jev showed effective immunity against JEV upon intranasal immunization in BALB/c mice. The rNDVs vaccination produced effective neutralization antibody titers against both NDV and JEV. The cytokine profiling of the vaccinated mice showed an effective Th1 and Th2 mediated immune response. The study also provided an insight that E, when used in combination with NS1 could reduce the efficacy of only E based immunization in mice. Our results suggested rNDV-Ejev to be a promising live viral vectored vaccine against JEV. This study implies an alternative and economical strategy for the development of a recombinant vaccine against JEV.

Introduction of the Japanese encephalitis virus (JEV) in the United States - A qualitative risk assessment

The purpose of this risk assessment (RA) was to qualitatively estimate the risk of emergence of the Japanese encephalitis virus (JEV) in the United States (US). We followed the framework for RA of emerging vector-borne livestock diseases (de Vos et al. 2011), which consists of a structured questionnaire, whose answers to questions can be delivered in risk categories, descriptive statements, or yes or no type of answers, being supported by the literature. The most likely pathways of introduction of JEV identified were: (a) entry through infected vectors (by aircraft, cargo ships, tires, or wind); (b) import of infected viremic animals; (c) entry of viremic migratory birds; (d) import of infected biological materials; (e) import of infected animal products; (f) entry of infected humans; and (g) import/production of contaminated biological material (e.g., vaccines). From these pathways, the probability of introduction of JEV through infected adult mosquitoes via aircraft was considered very high and via ships/containers was deemed low to moderate. The probability of introduction via other pathways or modes of entry (vector eggs or larvae, hosts, and vaccines) was considered negligible. The probability of transmission of JEV was variable, ranging from low to high (in the presence of both competent vectors and hosts), depending on the area of introduction within the US. Lastly, the probability of establishment of JEV in the continental US was considered negligible. For that reason, we stopped the risk assessment at this point of the framework. This RA provides important information regarding the elements that contribute to the risk associated with the introduction of JEV in the US. This RA also indicates that infected mosquitoes transported in aircraft (and cargo ships) are the most likely pathway of JEV entry and therefore, mitigation strategies should be directed towards this pathway.

A quantitative risk assessment (QRA) of the risk of introduction of the Japanese encephalitis virus (JEV) in the United States via infected mosquitoes transported in aircraft and cargo ships

Following a qualitative risk assessment, in which we identified and assessed all viable pathways for the introduction of the Japanese encephalitis virus (JEV) into the United States (US), we identified entry through infected vectors via aircraft and cargo ships as the most likely pathway, and thus considered it further in a quantitative risk assessment (QRA) model. The objective of this study was to evaluate the risk of introduction of JEV in the US via infected mosquitoes transported in aircraft and cargo ships arriving from Asia, using a QRA model. We created a stochastic model to quantify the probability of introduction of at least one infected mosquito in the continental US via aircraft and cargo ships, per at-risk period (March to October) or year, respectively. We modeled the following parameters: number of flights (per at-risk period, i.e., March to October) and cargo ships (per year) and per region, number of mosquitoes per flight and ship, number of mosquitoes that were not found and sensitivity of the mosquito collection method in aircraft, mosquito infection rates, and number of mosquitoes coming in aircraft per at-risk period (March to October) and cargo ships per year. Flight and cargo ship data pertained to years 2010-2016. For model building purposes, we only considered port-to-port vessels arriving from Asia to the US, we assumed that mosquitoes survive the trans-Pacific Ocean ship crossing and that the number of mosquitoes in cargo and passenger flights is similar. Our model predicted a very high risk (0.95 median probability; 95% CI = 0.80-0.99) of at least one infected mosquito being introduced in the US during the at-risk period, i.e., March to October, via aircraft transportation from JEV-affected countries in Asia. We also estimated that a median of three infected mosquitoes can enter the US during the at-risk period, i.e., March to October (95% CI = 1-7). The highest probability of introduction via aircraft was attributed to the Mediterranean California ecoregion (0.74; 95% CI = 0.50-0.90). We predicted, however, a negligible risk (0; 95% CI = 0.00-0.01) of at least one infected mosquito being introduced via cargo ships. Although the risk of introduction of JEV-infected mosquitoes by cargo ships was negligible, the risk via aircraft was estimated to be high. Our findings indicate the need to prioritize JEV prevention and control methods for aircraft-based pathways, such as aircraft disinfection. The quantitative estimates provided in this study are of interest to public health entities and other stakeholders, as they may support future interventions for preventing JEV introduction, as well as other vector-borne diseases, in the US and other countries.

Meta-Analyses of Japanese Encephalitis Virus Infection, Dissemination, and Transmission Rates in Vectors

The objective of this work was to summarize and quantify Japanese encephalitis virus (JEV) infection, dissemination, and transmission rates in mosquitoes, using a meta-analysis approach. Data were obtained from experimental studies, gathered by means of a systematic review of the literature. Random-effects subgroup meta-analysis models by mosquito species were fitted to estimate pooled estimates and to calculate the variance between studies for three outcomes of interest: JEV infection, dissemination, and transmission rates in mosquitoes. To identify sources of heterogeneity among studies and to assess the association between different predictors (mosquito species, virus administration route, incubation period, and diagnostic method) with the outcome JEV infection rate in vectors, we fitted univariable meta-regression models. Mosquito species and administration route represented the main sources of heterogeneity associated with JEV infection rate in vectors. This study provided summary effect size estimates to be used as reference for other investigators when assessing transmission efficiency of vectors and explored sources of variability for JEV infection rates in vectors. Because transmission efficiency, as part of vector competence assessment, is an important parameter when studying the relative contribution of vectors to JEV transmission, our findings contribute to further our knowledge, potentially moving us toward more informed and targeted actions to prevent and control JEV in both affected and susceptible regions worldwide.