Recent and historical trends in the epidemiology of Japanese encephalitis and its implication for risk assessment in travellers

Seroprevalence of Japanese encephalitis virus in pig populations of Tamil Nadu, India: Exploring the tropical endemic link of virus

Japanese encephalitis virus (JEV) is a major cause of encephalitis in Southeast Asia. Tamil Nadu, a state located in the southern part of India, contributes substantially to the national burden of human JE cases every year. However, limited information is available on the epidemiology of JE in pig populations of Tamil Nadu. A cross-sectional study was conducted to assess JEV prevalence in pig populations of Tamil Nadu. A total of 710 pigs reared in 118 farms across 10 districts of Tamil Nadu were sampled using multistage cluster random sampling. Serum samples were analyzed for their JEV status using Immunoglobulin M (IgM) and Immunoglobulin G (IgG) Enzyme-Linked Immunosorbent Assay (ELISA). At the animal-level, the apparent JEV seroprevalence was 60.4% (95% CI: 56.8% - 64.0%) and the true seroprevalence was 50.1% (95% CI: 47.0% - 53.2%). The herd-level apparent seroprevalence was 94.1% (95% CI: 88.1% - 97.5%) and the true seroprevalence was 93.3% (95% CI: 89.5% - 96.2%). The intensity of JEV circulation was high in all the districts, with seroprevalence ranging between 43% and 100%. Pigs across all age categories were seropositive and a high overall seroprevalence of 95.2% (95% CI: 76.2% - 99.9%) was recorded in pigs older than 12 months. JEV seropositivity was recorded in all the seasons but the prevalence peaked in the monsoon (67.9%, 95% CI: 61.1% - 74.2%) followed by winter (65.1%, 95%CI: 57.4% - 72.2%) and summer (53.3%, 95% CI: 47.8% - 58.8%) seasons. The results indicate that JEV is endemic in pigs populations of the state and a one health approach is essential with collaborative actions from animal and public health authorities to control JE in Tamil Nadu, India.

Japanese encephlu emergence in Australia: the potential population at risk

Japanese encephalitis virus (JEV), an RNA virus transmitted by Culex mosquitoes, primarily cycles between aquatic birds and mosquitoes with pigs as amplifying hosts, posing a significant global encephalitis threat. The emergence and spread of the JEV in new epidemiological regions, such as recent cases in Australia and nonendemic areas like Pune, India, raise significant concerns. With an estimated 68 000 clinical cases and 13 600 to 20 400 deaths annually, JEV poses a substantial global health threat. The virus primarily affects children, with a case-fatality ratio of 20-30% and long-term neurological sequelae in survivors. The changing epidemiology, influenced by factors like bird migration, climate change, and increased urbanization, contributes to the geographic expansion of JEV. The recent outbreaks underscore the potential for the virus to establish itself in nonendemic regions, posing a threat to populations previously considered at low-risk. With limited treatment options and high rates of neurological complications, continued surveillance, traveler vaccination, and research into treatments are crucial to mitigate the impact of JEV on human health. The evolving scenario necessitates proactive measures to prevent and control the spread of the virus in both endemic and newly affected areas.

Comparative genomics of Japanese encephalitis virus shows low rates of recombination and a small subset of codon positions under episodic diversifying selection

Orthoflavivirus japonicum (JEV) is the dominant cause of viral encephalitis in the Asian region with 100,000 cases and 25,000 deaths reported annually. The genome is comprised of a single polyprotein that encodes three structural and seven non-structural proteins. We collated a dataset of 349 complete genomes from a number of public databases, and analysed the data for recombination, evolutionary selection and phylogenetic structure. There are low rates of recombination in JEV, subsequently recombination is not a major evolutionary force shaping JEV. We found a strong overall signal of purifying selection in the genome, which is the main force affecting the evolutionary dynamics in JEV. There are also a small number of genomic sites under episodic diversifying selection, especially in the envelope protein and non-structural proteins 3 and 5. Overall, these results support previous analyses of JEV evolutionary genomics and provide additional insight into the evolutionary processes shaping the distribution and adaptation of this important pathogenic arbovirus.

Travel vaccines-priorities determined by incidence and impact

BACKGROUND

Infectious disease epidemiology is continuously shifting. While travel has been disrupted by the COVID-19 pandemic and travel-related epidemiological research experienced a pause, further shifts in vaccine-preventable diseases (VPDs) relevant for travellers have occurred.

METHODS

We conducted a literature search on the epidemiology of travel-related VPD and synthesized data for each disease with a focus on symptomatic cases and on the impact of the respective infection among travellers, considering the hospitalization rate, disease sequela and case fatality rate. We present new data and revised best estimates on the burden of VPD relevant for decisions on priorities in travel vaccines.

RESULTS

COVID-19 has emerged to be a top travel-related risk and influenza remains high in the ranking with an estimated incidence at 1% per month of travel. Dengue is another commonly encountered infection among international travellers with estimated monthly incidence of 0.5-0.8% among non-immune exposed travellers; the hospitalized proportion was 10 and 22%, respectively, according to two recent publications. With recent yellow fever outbreaks particularly in Brazil, its estimated monthly incidence has risen to >0.1%. Meanwhile, improvements in hygiene and sanitation have led to some decrease in foodborne illnesses; however, hepatitis A monthly incidence remains substantial in most developing regions (0.001-0.01%) and typhoid remains particularly high in South Asia (>0.01%). Mpox, a newly emerged disease that demonstrated worldwide spread through mass gathering and travel, cannot be quantified regarding its travel-related risk.

CONCLUSION

The data summarized may provide a tool for travel health professionals to prioritize preventive strategies for their clients against VPD. Updated assessments on incidence and impact are ever more important since new vaccines with travel indications (e.g. dengue) have been licensed or are undergoing regulatory review.

Japanese Encephalitis Vaccine Acceptance and Strategies for Travelers: Insights from a Scoping Review and Practitioners in Endemic Countries

Japanese encephalitis (JE) remains the cause of vaccine-preventable encephalitis in individuals living in endemic areas and international travelers. Although rare, the disease's high fatality rate emphasizes the need for effective immunization. This review aims to provide updated data on the JE burden between 2017 and 2023, vaccine acceptance, and vaccine strategies for travelers. We prospectively identified studies, using MEDLINE and PubMed, published through 2023. JE incidence has decreased in local populations and remains low among travelers from non-endemic countries. The local JE risk cannot be utilized to determine traveler risk. Adult travelers naïve to JEV infection or immunization may be at potentially higher risk. The JE vaccine acceptance rates among international travelers visiting JE endemic areas range from 0.2% to 28.5%. The cost of the vaccine and low risk perception could be barriers to JE vaccination. For travelers, an accelerated two-dose regimen of inactivated Vero cell JE vaccine (JE-VC) or a single dosage of live attenuated JE vaccine (JE-LV) may be an option. In conclusion, the JE burden among residents and travelers is lower, but the risk is not negligible. Practitioners should prioritize sharing knowledge, increasing awareness, and promoting vaccinations and preventive measures to reduce tourists' risk of JE along their journey.

Adults in Northwest China experienced the largest outbreak of Japanese encephalitis in history 10 years after the Japanese encephalitis vaccine was included in the national immunization program: A retrospective epidemiological study

Mainland China included Japanese encephalitis (JE) vaccine in the national immunization program in 2008 to control the JE epidemic. However, Gansu province in Western China experienced the largest JE outbreak since 1958 in 2018. We conducted a retrospective epidemiological study to explore the causes of this outbreak. We found that adults aged ≥20 years (especially those in rural areas) were the main JE cases in Gansu Province, with a significant increase in the JE incidence in older adults aged ≥60 years in 2017 and 2018. In addition, JE outbreaks in Gansu Province were mainly located in the southeastern region, while the temperature and precipitation in Gansu Province were gradually increasing in recent years, which made the JE epidemic areas in Gansu Province gradually spread to the western of Gansu Province. We also found that adults aged ≥20 years in Gansu Province had lower JE antibody positivity than children and infants, and the antibody positivity rate decreased with age. In the summer of 2017 and 2018, the density of mosquitoes (mainly the Culex tritaeniorhynchus) in Gansu Province was significantly higher than in other years, and the genotype of JEV was mainly Genotype-G1. Therefore, in the future JE control in Gansu Province, we need to strengthen JE vaccination for adults. Moreover, strengthening mosquito surveillance can provide early warning of JE outbreaks and the spread of epidemic areas in Gansu Province. At the same time, strengthening JE antibody surveillance is also necessary for JE control.

The evolving Japanese encephalitis situation in Australia and implications for travel medicine

The recent emergence of Japanese encephalitis in south-eastern Australia highlights the changing epidemiology of this important disease and the need for integrated surveillance to inform risk-based discussions and vaccination advice for travellers and endemic populations.

Molecular Mechanism and Role of Japanese Encephalitis Virus Infection in Central Nervous System-Mediated Diseases

The Japanese encephalitis virus (JEV) is the most common cause of neurodegenerative disease in Southeast Asia and the Western Pacific region; approximately 1.15 billion people are at risk, and thousands suffer from permanent neurological disorders across Asian countries, with 10-15 thousand people dying each year. JEV crosses the blood-brain barrier (BBB) and forms a complex with receptors on the surface of neurons. GRP78, Src, TLR7, caveolin-1, and dopamine receptor D2 are involved in JEV binding and entry into the neurons, and these receptors also play a role in carcinogenic activity in cells. JEV binds to GRP78, a member of the HSP70 overexpressed on malignant cells to enter neurons, indicating a higher chance of JEV infection in cancer patients. However, JEV enters human brain microvascular endothelial cells via an endocytic pathway mediated by caveolae and the ezrin protein and also targets dopamine-rich areas for infection of the midbrain via altering dopamine levels. In addition, JEV complexed with CLEC5A receptor of macrophage cells is involved in the breakdown of the BBB and central nervous system (CNS) inflammation. CLEC5A-mediated infection is also responsible for the influx of cytokines into the CNS. In this review, we discuss the neuronal and macrophage surface receptors involved in neuronal death.

Seroepidemiological study of Japanese encephalitis virus in Chiang Mai: Immunity and susceptibility 28 years after introduction of a vaccination programme

Background

Thailand has introduced a nationwide vaccination against Japanese encephalitis virus (JEV) into National Immunization Programme since the 1990’s. To improve the understanding of immunity and susceptibility of the population after 28 years of a vaccination programme, we conducted a JEV seroepidemiological study in a JEV-endemic area of Thailand.

Methods

An age-stratified, population-based, seroepidemiological study was conducted in Chiang Mai, Thailand–a northern Thai province where is an endemic area of Japanese encephalitis. Nine districts were chosen based on administrative definition: rural (n = 3); urban (n = 3); and peri-urban (n = 3). Within each district, eligible participants were randomly selected from 3 age groups: adolescents (10–20 years); adults (21–50 years); and older adults/elderly (≥51 years) by computer randomization. Plaque reduction neutralization tests (PRNT50 and PRNT90) were performed to measure neutralizing antibodies to JEV. To account for the cross-reactivity of JEV and other flaviviruses, JEV seroprotection was defined according to age, previous history of JEV vaccination, and PRNT50/PRNT90 levels of study participants.

Results

Overall, 279 adolescents, 297 adults, and 297 older adults/elderly were enrolled from nine districts. Age-stratified, protocol-defined, cluster-adjusted JEV seroprotection rates were 61% (95% CI: 48–73%), 43% (95% CI: 31–57%), and 52% (95% CI: 37–67%) for adolescents, adults, and older adults/elderly, respectively. Living in peri-urban districts, having a history of prior dengue virus infection, and previously receiving mouse brain-derived JEV vaccine were significantly associated with seroprotection to JEV in adolescents. Older age and male sex were associated with seroprotection for adults; and only male sex was the associated factor for older adults/elderly (P <0.05).

Conclusions

Approximately half of population living in a JEV-endemic area demonstrated seroprotection to JEV. Ongoing nationwide surveillance on JEV seropepidemiology is an important strategy to understand the evolving population-level immunity to JEV, and to help formulating the appropriate recommendations on JE immunization.

Japanese encephalitis virus persists in the human reproductive epithelium and porcine reproductive tissues

Japanese encephalitis virus (JEV) is the emerging and geographically expanding flavivirus and the major causative agent of encephalitis in humans in Asia. There are risks of JEV introduction into the Americas given a large population of amplifying hosts-pigs and wild boars, and insect vectors-Culex mosquitoes. There are emerging concerns about vector-free ways of flavivirus transmission, for example sexual and transplacental Zika virus transmissions, which may change flavivirus epidemiology and expand the geographical range to territories with no insect vectors. It is unknown whether JEV has tropism in the female lower reproductive tract and the potential for sexual transmission in humans. While clinical outcomes of transplacental JEV infection are described in humans and pigs, cellular targets and tissue tropism in the upper reproductive tract are also unknown. Here, we studied JEV infection phenotypes and host transcriptional responses in human reproductive epithelial cells. We found that JEV caused persistent infection and cytopathology in the vaginal epithelium, endometrial epithelium, and trophoblast. Human vaginal epithelial cells infected with JEV had altered transcriptional responses associated with inflammation and disruption of epithelial barrier function. Also, using pigs-the native amplifying host for JEV, we confirmed JEV tropism in the female lower and upper reproductive tracts. We discovered that JEV persists in the vaginal mucosa for at least 28 days and pigs shed the virus in vaginal secretions. We also found JEV persistence in the endometrium and placenta with transplacental and fetal infections. Altogether, we discovered that JEV targets the vaginal epithelium and has the potential for sexual transmission in humans. We also contributed to a better understanding of JEV pathogenesis during transplacental infection. Further studies are needed to better understand the interactions of JEV with reproductive tissues, how persistent infection affects female reproductive functions, and the risks for non-vector transmission.

Joint spatiotemporal modelling reveals seasonally dynamic patterns of Japanese encephalitis vector abundance across India

Predicting vector abundance and seasonality, key components of mosquito-borne disease (MBD) hazard, is essential to determine hotspots of MBD risk and target interventions effectively. Japanese encephalitis (JE), an important MBD, is a leading cause of viral encephalopathy in Asia with 100,000 cases estimated annually, but data on the principal vector Culex tritaeniorhynchus is lacking. We developed a Bayesian joint-likelihood model that combined information from available vector occurrence and abundance data to predict seasonal vector abundance for C. tritaeniorhynchus (a constituent of JE hazard) across India, as well as examining the environmental drivers of these patterns. Using data collated from 57 locations from 24 studies, we find distinct seasonal and spatial patterns of JE vector abundance influenced by climatic and land use factors. Lagged precipitation, temperature and land use intensity metrics for rice crop cultivation were the main drivers of vector abundance, independent of seasonal, or spatial variation. The inclusion of environmental factors and a seasonal term improved model prediction accuracy (mean absolute error [MAE] for random cross validation = 0.48) compared to a baseline model representative of static hazard predictions (MAE = 0.95), signalling the importance of seasonal environmental conditions in predicting JE vector abundance. Vector abundance varied widely across India with high abundance predicted in northern, north-eastern, eastern, and southern regions, although this ranged from seasonal (e.g., Uttar Pradesh, West Bengal) to perennial (e.g., Assam, Tamil Nadu). One-month lagged predicted vector abundance was a significant predictor of JE outbreaks (odds ratio 2.45, 95% confidence interval: 1.52–4.08), highlighting the possible development of vector abundance as a proxy for JE hazard. We demonstrate a novel approach that leverages information from sparse vector surveillance data to predict seasonal vector abundance–a key component of JE hazard–over large spatial scales, providing decision-makers with better guidance for targeting vector surveillance and control efforts.

Japanese encephalitis (JE) is the leading cause of viral encephalopathy in Asia with an estimated 100,000 annual cases and 25,000 deaths. However, insufficient data on the predominant mosquito vector Culex tritaeniorhynchus–a key component of JE hazard–precludes hazard estimation required to target public health interventions. Previous studies have provided limited estimates of JE hazard, often predicting geographic distributions of potential vector occurrence without accounting for vector abundance, seasonality, or uncertainty in predictions. This study details a novel approach to predict spatiotemporal patterns in JE vector abundance using a joint-likelihood modelling technique that leverages information from sparse vector surveillance data. We showed that patterns in JE vector abundance were driven by seasonality and environmental factors and so demonstrated the limitations of previously available static vector distribution maps in estimating the vector population component of JE hazard. One-month lagged vector abundance predictions showed a positive relationship with JE outbreaks, signalling the potential use of vector abundance as a proxy for JE hazard. While vector surveillance data are limited, joint-likelihood models offer a useful approach to inform vector abundance predictions. This study provides decision-makers with a more complete picture of the distribution of JE vector abundance and can be used to target vector surveillance and control efforts and enhance the allocation of resources.

Vaccines and Senior Travellers

Background: International tourist travel has been increasingly steadily in recent years, and looks set to reach unprecedented levels in the coming decades. Among these travellers, an increasing proportion is aged over 60 years, and is healthy and wealthy enough to be able to travel. However, senior travellers have specific risks linked to their age, health and travel patterns, as compared to their younger counterparts. Methods: We review here the risk of major vaccine-preventable travel-associated infectious diseases, and forms and efficacy of vaccination for these diseases. Results: Routine vaccinations are recommended for older persons, regardless of whether they travel or not (e.g., influenza, pneumococcal vaccines). Older individuals should be advised about the vaccines that are recommended for their age group in the framework of the national vaccination schedule. Travel-specific vaccines must be discussed in detail on a case-by-case basis, and the risk associated with the vaccine should be carefully weighed against the risk of contracting the disease during travel. Travel-specific vaccines reviewed here include yellow fever, hepatitis, meningococcal meningitis, typhoid fever, cholera, poliomyelitis, rabies, Japanese encephalitis, tick-borne encephalitis and dengue. Conclusion: The number of older people who have the good health and financial resources to travel is rising dramatically. Older travellers should be advised appropriately about routine and travel-specific vaccines, taking into account the destination, duration and purpose of the trip, the activities planned, the type of accommodation, as well as patient-specific characteristics, such as health status and current medications.

Outbreak prone communicable diseases of public health importance in the northern districts of West Bengal - Current status & the way forward

India is perilously poised on the threshold of an explosion of infectious diseases, some of which have witnessed re-emergence while others await apposite opportunity to do so. The State of West Bengal is uniquely positioned with its innate geographical vulnerabilities that favour outbreaks of a host of infectious diseases. The northern districts of this State are well known endemic areas for many outbreak prone communicable diseases like malaria, Japanese encephalitis, scrub typhus, dengue and kala-azar. An outbreak of Nipah virus in the recent past is a pointer towards the emerging and re-emerging threat in these regions and warrants urgent prioritization for surveillance and monitoring of these diseases. Identification of risk factors, challenges in delivery of primary healthcare, implementation of intervention strategies along with strengthening of healthcare setup are also the need of the hour. Multisectoral initiatives with emphasis on understanding the complex and rapidly evolving human-animal-vector dynamics as envisaged under the ‘One Health’ concept are indubitably important pillars in the effective management of these emerging public health challenges.

Screening of ZIKA virus infection among dengue-like illness patients with negative RT-PCR for dengue virus in Punjab - Pakistan

Objective

To detect ZIKV using reverse transcription-polymerase chain reaction (RT-PCR) among clinical samples tested negative for Dengue virus (DENV) by RT-PCR in Punjab, 2016.

Methods

A descriptive cross-sectional study was carried out for duration of two months. Total of 506 samples were collected within seven days from onset of illness from all over hospitals of Punjab, Pakistan of which 350 were selected simply randomly to test for presence of ZIKV by using "Trioplex Real-Time RT-PCR Assay (Trioplex)". Cohen's kappa coefficient (κ) and 95% confidence interval (CI) were used to assess the degree of concordance between DENV positive results of non-structural protein 1 (NS1) and IgM solid-phase enzyme immunoassay (ELISA).

Results

No samples were positive for any ZIKV, DENV or Chikungunya virus (CHIKV) by Trioplex. Among the 350 samples, 26 samples were positive concordant and the degree of concordance between NS1- and IgM-ELISA was 13% and κ coefficient was -0.71 (95% CI -0.79, -0.63).

Conclusion

At study time, no samples were positive for ZIKV. Strengthening laboratory capacity to confirm arboviruses for Punjab's laboratories is warranted. Trioplex RT-PCR has 100% sensitivity so there are nominal chances of false negative results. Establishing syndromic surveillance for Zika and conducting a sero-surveillance survey for Zika in areas with high human and Aedes mosquito density are recommended in Punjab.

Role of Zoo-Housed Animals in the Ecology of Ticks and Tick-Borne Pathogens-A Review

Ticks are ubiquitous ectoparasites, feeding on representatives of all classes of terrestrial vertebrates and transmitting numerous pathogens of high human and veterinary medical importance. Exotic animals kept in zoological gardens, ranches, wildlife parks or farms may play an important role in the ecology of ticks and tick-borne pathogens (TBPs), as they may serve as hosts for local tick species. Moreover, they can develop diseases of varying severity after being infected by TBPs, and theoretically, can thus serve as reservoirs, thereby further propagating TBPs in local ecosystems. The definite role of these animals in the tick-host-pathogen network remains poorly investigated. This review provides a summary of the information currently available regarding ticks and TBPs in connection to captive local and exotic wildlife, with an emphasis on zoo-housed species.

Superinfection Exclusion in Mosquitoes and Its Potential as an Arbovirus Control Strategy

The continuing emergence of arbovirus disease outbreaks around the world, despite the use of vector control strategies, warrants the development of new strategies to reduce arbovirus transmission. Superinfection exclusion, a phenomenon whereby a primary virus infection prevents the replication of a second closely related virus, has potential to control arbovirus disease emergence and outbreaks. This phenomenon has been observed for many years in plants, insects and mammalian cells. In this review, we discuss the significance of identifying novel vector control strategies, summarize studies exploring arbovirus superinfection exclusion and consider the potential for this phenomenon to be the basis for novel arbovirus control strategies.

Dengue vaccine development by the year 2020: challenges and prospects

The first licensed dengue vaccine led to considerable controversy, and to date, no dengue vaccine is in widespread use. All three leading dengue vaccine candidates are live attenuated vaccines, with the main difference between them being the type of backbone and the extent of chimerization. While CYD-TDV (the first licensed dengue vaccine) does not include non-structural proteins of dengue, TAK-003 contains the dengue virus serotype 2 backbone, and the Butantan/Merck vaccine contains three full-genomes of the four dengue virus serotypes. While dengue-primed individuals can already benefit from vaccination against all four serotypes with the first licensed dengue vaccine CYD-TDV, the need for dengue-naive population has not yet been met. To improve tetravalent protection, sequential vaccination should be considered in addition to a heterologous prime-boost approach.

The Pretravel Consultation: Recent Updates

Estimates suggest that 43%-79% of international travelers may develop travel-related illnesses. Most such illnesses are considered mild and self-limited; however, some are life-threatening. The pretravel consultation is aimed at assessing risks for a range of illnesses, communicating these risks, and then providing individualized recommendations and interventions to minimize or manage such risks. The effective consultation is predicated on a well-prepared clinician and motivated traveler, understanding the traveler's perception of, and tolerance for, risk, and providing education applicable to the actual itinerary. Integral to the clinician's preparation is regular review of up-to-date trip-specific recommendations; country-specific information and recommendations are readily available and can now be efficiently accessed. From the infectious diseases perspective, immunizations, malaria chemoprophylaxis, insect repellent use, and travelers' diarrhea and its self-management are cornerstones of the consultation. This review focuses primarily on updating these 4 topics with recently published information relevant to adult travelers.

Are all vaccines safe for the pregnant traveller? A systematic review and meta-analysis

Pregnant travellers and their offspring are vulnerable to severe outcomes following a wide range of infections. Vaccine-preventable diseases can have a particularly severe course in pregnant women, but little is known about the safety of travel vaccines in pregnant women. We performed a systematic review of all published literature concerning the safety of vaccines frequently given to travellers such as yellow fever, MMR (mumps, measles and rubella), influenza, Tdap (tetanus, diphtheria and pertussis), meningococcus, hepatitis A and B, rabies, polio, typhoid fever, tick-borne encephalitis and Japanese encephalitis vaccines. We included case series, cohort studies and randomized controlled trials (RCTs). For the meta-analysis, we included only RCTs that compared the administration of a vaccine to placebo or to no vaccine. Outcome measures included severe systemic adverse events, maternal outcomes related to the course of pregnancy, neonatal outcomes and local adverse events. We calculated the risk ratio and its 95% confidence interval as the summary measure. The safety of influenza vaccine is supported by high-quality evidence. For Tdap vaccine, no evidence of any harm was found in the meta-analysis of RCTs. A slight increase in chorioamnionitis rate was reported in 3 out of 12 observational studies. However, this small possible risk is far outweighed by a much larger benefit in terms of infant morbidity and mortality. Meningococcal vaccines are probably safe during pregnancy, as supported by RCTs comparing meningococcal vaccines to other vaccines. Data from observational studies support the safety of hepatitis A, hepatitis B and rabies vaccines, as well as that of the live attenuated yellow fever vaccine. We found little or no data about the safety of polio, typhoid, Japanese encephalitis, tick-borne encephalitis and MMR vaccines during pregnancy.

The immunosuppressed traveler: infection risks with autoimmunity and immunosuppression, vaccinations, and general travel advice

The travel-related infection risks in the significantly immunocompromised traveler are complex and comprise vaccine preventable, vector-borne, and other nonvaccine preventable infections. A thorough risk assessment should be performed before travel and advice sought from relevant specialists. Immunosuppression used to treat autoimmune diseases and their mechanisms of action need particular consideration.This risk assessment needs to take the patient's beliefs and preferences into account. It is also important not to neglect noninfectious travel considerations.

The Envelope Residues E152/156/158 of Zika Virus Influence the Early Stages of Virus Infection in Human Cells

Emerging infections of mosquito-borne Zika virus (ZIKV) pose an increasing threat to human health, as documented over the recent years in South Pacific islands and the Americas in recent years. To better understand molecular mechanisms underlying the increase in human cases with severe pathologies, we recently demonstrated the functional roles of structural proteins capsid (C), pre-membrane (prM), and envelop (E) of ZIKV epidemic strains with the initiation of viral infection in human cells. Specifically, we found that the C-prM region contributes to permissiveness of human host cells to ZIKV infection and ZIKV-induced cytopathic effects, whereas the E protein is associated with viral attachment and early infection. In the present study, we further characterize ZIKV E proteins by investigating the roles of residues isoleucine 152 (Ile152), threonine 156 (Thr156), and histidine 158 (His158) (i.e., the E-152/156/158 residues), which surround a unique N-glycosylation site (E-154), in permissiveness of human host cells to epidemic ZIKV infection. For comparison purpose, we generated mutant molecular clones of epidemic BeH819015 (BR15) and historical MR766-NIID (MR766) strains that carry each other's E-152/156/158 residues, respectively. We observed that the BR15 mutant containing the E-152/156/158 residues from MR766 was less infectious in A549-Dual™ cells than parental virus. In contrast, the MR766 mutant containing E-152/156/158 residues from BR15 displayed increased infectivity. The observed differences in infectivity were, however, not correlated with changes in viral binding onto host-cells or cellular responses to viral infection. Instead, the E-152/156/158 residues from BR15 were associated with an increased efficiency of viral membrane fusion inside infected cells due to conformational changes of E protein that enhance exposure of the fusion loop. Our data highlight an important contribution of E-152/156/158 residues to the early steps of ZIKV infection in human cells.

Vaccines for International Travel

The pretravel management of the international traveler should be based on risk management principles. Prevention strategies and medical interventions should be based on the itinerary, preexisting health factors, and behaviors that are unique to the traveler. A structured approach to the patient interaction provides a general framework for an efficient consultation. Vaccine-preventable diseases play an important role in travel-related illnesses, and their impact is not restricted to exotic diseases in developing countries. Therefore, an immunization encounter before travel is an ideal time to update all age-appropriate immunizations as well as providing protection against diseases that pose additional risk to travelers that may be delineated by their destinations or activities. This review focuses on indications for each travel-related vaccine together with a structured synthesis and graphics that show the geographic distribution of major travel-related diseases and highlight particularly high-risk destinations and behaviors. Dosing, route of administration, need for boosters, and possible accelerated regimens for vaccines administered prior to travel are presented. Different underlying illnesses and medications produce different levels of immunocompromise, and there is much unknown in this discipline. Recommendations regarding vaccination of immunocompromised travelers have less of an evidence base than for other categories of travelers. The review presents a structured synthesis of issues pertinent to considerations for 5 special populations of traveler: child traveler, pregnant traveler, severely immunocompromised traveler, HIV-infected traveler, and traveler with other chronic underlying disease including asplenia, diabetes, and chronic liver disease.

'More than devastating'-patient experiences and neurological sequelae of Japanese encephalitis§

BACKGROUND

Japanese encephalitis (JE), caused by the mosquito-borne JE virus, is a vaccine-preventable disease endemic to much of Asia. Travellers from non-endemic areas are susceptible if they travel to a JE endemic area. Although the risk to travellers of JE is low, the consequences may be severe.

METHODS

Here, we describe three cases of JE in British travellers occurring in 2014-15. In addition, we report, through interviews with survivors and their families, personal experiences of life after JE.

RESULTS

Three cases of JE were diagnosed in British travellers in 2014/15. One was acquired in Thailand, one in China and one in either Thailand, Laos or Cambodia. All three patients suffered severe, life-threatening illnesses, all were admitted to intensive care units and required medical evacuation back to the UK. One patient suffered a cardiac arrest during the acute stage but made a good recovery. The other two patients remain significantly paralysed and ventilator dependent. All three cases had clear indications for vaccination, and all have been left with life-changing neurological sequelae.

CONCLUSIONS

Travel health providers should be aware of the severity of JE, as well as the risk, allowing travellers to make fully informed decisions on JE vaccination.

Travel vaccination recommendations and infection risk in HIV-positive travellers

BACKGROUND

With the advent of highly active antiretroviral drugs for the treatment of human immunodeficiency virus (HIV) it has become possible for people with HIV to travel to destinations that may place them at risk of a number of infectious diseases. Prevention of infections by vaccination is therefore of paramount importance for these travellers. However, vaccine responsiveness in HIV-positive individuals is not infrequently reduced compared to HIV-negative individuals. An understanding of the expected immune responses to vaccines in HIV-positive travellers is therefore important in planning the best approach to a pretravel consultation.

METHODS

A PubMed search was performed on HIV or acquired immune deficiency syndrome together with a search for specific vaccines. Review of the literature was performed to develop recommendations on vaccinations for HIV-positive travellers to high-risk destinations.

RESULTS

The immune responses to several vaccines are reduced in HIV-positive people. In the case of vaccines for hepatitis A, hepatitis B, influenza, pneumococcus, meningococcus and yellow fever there is a good body of data in the literature showing reduced immune responsiveness and also to help guide appropriate vaccination strategies. For other vaccines like Japanese encephalitis, rabies, typhoid fever, polio and cholera the data are not as robust; however, it is still possible to gain some understanding of the reduced responses seen with these vaccines.

CONCLUSION

This review provides a summary of the immunological responses to commonly used vaccines for the HIV-positive travellers. This information will help guide travel medicine practitioners in making decisions about vaccination and boosting of travellers with HIV.

Incidence of Guillain-Barré Syndrome (GBS) in Latin America and the Caribbean before and during the 2015-2016 Zika virus epidemic: A systematic review and meta-analysis

BACKGROUND

A severe neurological disorder, Guillain-Barré syndrome (GBS) is the leading cause of acute flaccid paralysis. Enhanced surveillance of GBS in Latin America and the Caribbean (LAC) following the 2015-2016 Zika virus (ZIKV) epidemic presents an opportunity to estimate, for the first time, the regional incidence of GBS.

METHODS AND FINDINGS

For this systematic review and meta-analysis, we searched nine scientific databases and grey literature from January 1, 1980 to October 1, 2018. Sources with primary data on incident GBS cases in LAC within a well-defined population and timeframe, published in English, Spanish, Portuguese, or French, were included. We calculated the annual GBS incidence rates (IRs) and 95% confidence intervals (CIs) for each source based on published data. Following an assessment of heterogeneity, we used random-effects meta-analysis to calculate the pooled annual IR of GBS. The study is registered with PROSPERO, number CRD42018086659. Of the 6568 initial citation hits, 31 were eligible for inclusion. Background annual GBS IRs in Latin America ranged from 0.40 in Brazil to 2.12/100,000 in Chile. The pooled annual IR in the Caribbean was 1.64 (95% CI 1.29-2.12, I2<0.01, p = 0.44). During the ZIKV epidemic, GBS IRs ranged from 0.62 in Mexico to 9.35/100,000 in Martinique. GBS increased 2.6 (95% CI 2.3-2.9) times during ZIKV and 1.9 (95% CI 1.1-3.4) times during chikungunya outbreaks over background rates. A limitation of this review is that the studies included employed different methodologies to find and ascertain cases of GBS, which could contribute to IR heterogeneity. In addition, it is important to consider that data on GBS are lacking for many countries in the region.

CONCLUSIONS

Background IRs of GBS appear to peak during arboviral disease outbreaks. The current review contributes to an understanding of the epidemiology of GBS in the LAC region, which can inform healthcare system planning and preparedness, particularly during arboviral epidemics.

TRIAL REGISTRATION

Registered with PROSPERO: CRD42018086659.

Japanese encephalitis: the vectors, ecology and potential for expansion

BACKGROUND

Japanese encephalitis (JE) is a viral disease predominantly located in South East Asia and commonly associated with transmission between amplifying hosts, such as pigs, and the mosquito Culex tritaeniorhynchus, where human infection represents a dead end in the life cycle of the virus. The expansion of JE beyond an Asiatic confine is dependent on a multitude of complex factors that stem back to genetic subtype variation. A complex interplay of the genetic variation and vector competencies combine with variables such as geography, climate change and urbanization.

METHODS

Our understanding of JE is still at an early stage with long-term longitudinal vector surveillance necessary to better understand the dynamics of JE transmission and to characterize the role of potential secondary vectors such as Cx. pipiens and Cx. bitaeniorhynchus. The authors review the vectors indicated in transmission and the ecological, genetic and anthropological factors that affect the disease's range and epidemiology.

CONCLUSION

Monitoring for the presence of JE virus in mosquitoes in general can be used to estimate levels of potential JE exposure, intensity of viral activity and genetic variation of JEV throughout surveyed areas. Increased surveillance and diagnosis of viral encephalitis caused by genotype 5 JE virus is required in particular, with the expansion in epidemiology and disease prevalence in new geographic areas an issue of great concern. Additional studies that measure the impact of vectors (e.g. bionomics and vector competence) in the transmission of JEV and that incorporate environmental factors (e.g. weekly rainfall) are needed to define the roles of Culex species in the viral pathogenesis during outbreak and non-outbreak years.

Overview of Japanese encephalitis disease and its prevention. Focus on IC51 vaccine (IXIARO®)

Japanese encephalitis (JE) is a vector-borne disease caused by the Japanese encephalitis virus (JEV). JEV is transmitted by mosquitoes to a wide range of vertebrate hosts, including birds and mammals. Domestic animals, especially pigs, are generally implicated as reservoirs of the virus, while humans are not part of the natural transmission cycle and cannot pass the virus to other hosts. Although JEV infection is very common in endemic areas (many countries in Asia), less than 1% of people affected develop clinical disease, and severe disease affects about 1 case per 250 JEV infections. Although rare, severe disease can be devastating; among the 30,000-50,000 global cases per year, approximately 20-30% of patients die and 30-50% of survivors develop significant neurological sequelae. JE is a significant public health problem for residents in endemic areas and may constitute a substantial risk for travelers to these areas. The epidemiology of JE and its risk to travelers have changed, and continue to evolve. The rapid economic growth of Asian countries has led to a surge in both inbound and outbound travel, making Asia the second most-visited region in the world after Europe, with 279 million international travelers in 2015. The top destination is China, followed by Thailand, Hong Kong, Malaysia and Japan, and the number of travelers is forecast to reach 535 million by 2030 (+ 4.9% per year). Because of the lack of treatment and the infeasibility of eliminating the vector, vaccination is recognized as the most efficacious means of preventing JE. The IC51 vaccine (IXIARO^®) is a purified, inactivated, whole virus vaccine against JE. It is safe, well tolerated, efficacious and can be administered to children, adults and the elderly. The vaccination schedule involves administering 2 doses four weeks apart. For adults, a rapid schedule (0-7 days) is available, which could greatly enhance the feasibility of its use. Healthcare workers should inform both short- and long-term travelers of the risk of JE in each period of the year and recommend vaccination. Indeed, it has been shown that short-term travelers are also at risk, not only in rural environments, but also in cities and coastal towns, especially in tourist localities where excursions to country areas are organized.