Japanese encephalitis after a 10-day holiday in Bali

Interventions for the Prevention and Treatment of Japanese Encephalitis

Purpose of Review

Japanese encephalitis (JE), a clinical indication of JE virus–induced brain inflammation, is the most prevalent cause of viral encephalitis in the world. This review gives a comprehensive update on the epidemiology, clinical features, therapeutic trials and approaches for preventing the spread of JE. It also outlines the different JE vaccines used in various countries and recommendations for administration of JE vaccines.

Recent Findings

According to the WHO, annual incidence of JE is estimated to be approximately 68,000 cases worldwide. It is widespread across Asia–Pacific, with a potential for worldwide transmission. In endemic locations, JE is believed to affect children below 6 years of age, but in newly affected areas, both adults and children are at risk due to a lack of protective antibodies. Various vaccines have been developed for the prevention of JE and are being administered in endemic countries.

Summary

JE is a neuroinvasive disease that causes symptoms ranging from simple fever to severe encephalitis and death. Despite a vast number of clinical trials on various drugs, there is still no complete cure available, and it can only be prevented by adequate vaccination. Various nanotechnological approaches for the prevention and treatment of JE are outlined in this review.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11908-022-00786-1.

Japanese encephalitis in Bali, Indonesia: ecological and socio-cultural perspectives

The increasing number of cases of acute encephalitis syndrome, a key presenting clinical sign of Japanese encephalitis infection in humans, along with increasing laboratory confirmed cases in Bali over recent years have led to the Indonesian government developing a national program of vaccination against Japanese encephalitis virus. In order to inform multidisciplinary management, a review was conducted to assess Japanese encephalitis virus-related cases in humans and animals including their determinants and detection in vectors. Along with published literature, key data from local authorized officers in Bali have been used to convey the recent situation of the disease. Related surveys detected up to 92% of the local children had antibodies against the virus with the annual incidence estimated to be 7.1 per 100,000 children. Additionally, reports on young and adult cases of infection within international travellers infected in Bali were documented with both non-fatal and fatal outcomes. Further seroprevalence surveys detected up to 90% with antibodies to the virus in animal reservoirs. The detection of the virus in certain Culex mosquito species and high levels of seropositivity may be associated with greater risk of the virus transmission to the human population. It was also highlighted that local sociocultural practices for agriculture and livestock were potentially associated with the high density of the vector and the reservoirs, which then may lead to the risk of the disease transmission in the ecology of Bali.

A Case of Japanese Encephalitis with a Fatal Outcome in an Australian Who Traveled from Bali in 2019

A severe case of Japanese encephalitis virus (JEV) infection, resulting in fatality, occurred in an unvaccinated Australian male traveler from Bali, Indonesia, in 2019. During hospitalisation in Australia, patient cerebrospinal fluid (CSF) yielded JEV-specific IgM antibodies and RNA, and an isolate of the virus. Ongoing transmission of JEV in Bali underscores this pathogen as a public health risk and the importance of appropriate health, vaccination and mosquito avoidance advice to prospective travelers to the region.

Japanese encephalitis virus infection in non-encephalitic acute febrile illness patients

Although Japanese encephalitis virus (JEV) is considered endemic in Indonesia, there are only limited reports of JEV infection from a small number of geographic areas within the country with the majority of these being neuroinvasive disease cases. Here, we report cases of JEV infection in non-encephalitic acute febrile illness patients from Bali, Indonesia. Paired admission (S1) and discharge (S2) serum specimens from 144 acute febrile illness patients (without evidence of acute dengue virus infection) were retrospectively tested for anti-JEV IgM antibody and confirmed by plaque reduction neutralization test (PRNT) for JEV infection. Twenty-six (18.1%) patients were anti-JEV IgM-positive or equivocal in their S2 specimens, of which 5 (3.5%) and 8 (5.6%) patients met the criteria for confirmed and probable JEV infection, respectively, based on PRNT results. Notably, these non-encephalitic JE cases were less likely to have thrombocytopenia, leukopenia, and lower hematocrit compared with confirmed dengue cases of the same cohort. These findings highlight the need to consider JEV in the diagnostic algorithm for acute febrile illnesses in endemic areas and suggest that JEV as a cause of non-encephalitic disease has likely been underestimated in Indonesia.

Japanese encephalitis virus (JEV) is an important cause of central nervous system (CNS) infections in Asia and is considered endemic in Indonesia. However, reports of JEV infection in non-encephalitic disease cases are lacking because diagnosis is difficult to confirm and JEV is rarely considered as a cause of non-encephalitic disease. Here, with robust serological testing, we identified cases of JEV infection in patients presenting at a regency hospital in Bali with fever but without symptoms of CNS infection. This finding supports the need to include JEV in routine clinical diagnostic algorithms for patients with fever in endemic areas.

A need to raise the bar - A systematic review of temporal trends in diagnostics for Japanese encephalitis virus infection, and perspectives for future research

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Japanese encephalitis virus (JEV) remains a leading cause of neurological infection in Asia.

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A systematic review identified 20,212 published human cases of laboratory-confirmed JEV infections from 205 studies.

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15,167 (75%) of cases were confirmed with the lowest confidence diagnostic test, i.e., level 3 or 4, or level 4.

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Only 109 (53%) of the studies reported contemporaneous testing for dengue-specific antibodies.

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A fundamental pre-requisite for the control of JE is lacking — that of a simple and specific diagnostic procedure that can be adapted for point-of-care tests and readily used throughout JE endemic regions of the world.

Objective

Japanese encephalitis virus infection (JE) remains a leading cause of neurological disease in Asia, mainly involving individuals living in remote areas with limited access to treatment centers and diagnostic facilities. Laboratory confirmation is fundamental for the justification and implementation of vaccination programs. We reviewed the literature on historical developments and current diagnostic capability worldwide, to identify knowledge gaps and instill urgency to address them.

Methods

Searches were performed in Web of Science and PubMed using the term 'Japanese encephalitis' up to 13th October 2019. Studies reporting laboratory-confirmed symptomatic JE cases in humans were included, and data on details of diagnostic tests were extracted. A JE case was classified according to confirmatory levels (Fischer et al., 2008; Campbell et al., 2011; Pearce et al., 2018; Heffelfinger et al., 2017), where level 1 represented the highest level of confidence.

Findings

20,212 published JE cases were identified from 205 studies. 15,167 (75%) of these positive cases were confirmed with the lowest-confidence diagnostic tests (level 3 or 4, or level 4). Only 109 (53%) of the studies reported contemporaneous testing for dengue-specific antibodies.

Conclusion

A fundamental pre-requisite for the control of JEV is lacking — that of a simple and specific diagnostic procedure that can be adapted for point-of-care tests and readily used throughout JE-endemic regions of the world.

Japanese Encephalitis Vaccine: Recommendations of the Advisory Committee on Immunization Practices

This report updates the 2010 recommendations from the CDC Advisory Committee on Immunization Practices (ACIP) regarding prevention of Japanese encephalitis (JE) among U.S. travelers and laboratory workers (Fischer M, Lindsey N, Staples JE, Hills S. Japanese encephalitis vaccines: recommendations of the Advisory Committee on Immunization Practices (ACIP). MMWR Recomm Rep 2010;59[No. RR-1]). The report summarizes the epidemiology of JE, describes the JE vaccine that is licensed and available in the United States, and provides recommendations for its use among travelers and laboratory workers.JE virus, a mosquitoborne flavivirus, is the most common vaccine-preventable cause of encephalitis in Asia. JE occurs throughout most of Asia and parts of the western Pacific. Approximately 20%-30% of patients die, and 30%-50% of survivors have neurologic, cognitive, or behavioral sequelae. No antiviral treatment is available.Inactivated Vero cell culture-derived JE vaccine (Ixiaro [JE-VC]) is the only JE vaccine that is licensed and available in the United States. In 2009, the U.S. Food and Drug Administration (FDA) licensed JE-VC for use in persons aged ≥17 years; in 2013, licensure was extended to include children aged ≥2 months.Most travelers to countries where the disease is endemic are at very low risk for JE. However, some travelers are at increased risk for infection on the basis of their travel plans. Factors that increase the risk for JE virus exposure include 1) traveling for a longer period; 2) travel during the JE virus transmission season; 3) spending time in rural areas; 4) participating in extensive outdoor activities; and 5) staying in accommodations without air conditioning, screens, or bed nets. All travelers to countries where JE is endemic should be advised to take precautions to avoid mosquito bites to reduce the risk for JE and other vectorborne diseases. For some persons who might be at increased risk for JE, the vaccine can further reduce the risk for infection. The decision about whether to vaccinate should be individualized and consider the 1) risks related to the specific travel itinerary, 2) likelihood of future travel to countries where JE is endemic, 3) high morbidity and mortality of JE, 4) availability of an effective vaccine, 5) possibility (but low probability) of serious adverse events after vaccination, and 6) the traveler's personal perception and tolerance of risk.JE vaccine is recommended for persons moving to a JE-endemic country to take up residence, longer-term (e.g., ≥1 month) travelers to JE-endemic areas, and frequent travelers to JE-endemic areas. JE vaccine also should be considered for shorter-term (e.g., <1 month) travelers with an increased risk for JE on the basis of planned travel duration, season, location, activities, and accommodations and for travelers to JE-endemic areas who are uncertain about their specific travel duration, destinations, or activities. JE vaccine is not recommended for travelers with very low-risk itineraries, such as shorter-term travel limited to urban areas or outside of a well-defined JE virus transmission season.

Japanese encephalitis in Indonesia: An update on epidemiology and transmission ecology

The Japanese Encephalitis (JE) virus circulation in Indonesia was first documented in Lombok in 1960, and the virus was first isolated in 1972 from Culex tritaeniorhynchus in Bekasi, West Java and Kapuk, West Jakarta. Since then, Indonesia has been recognized as an endemic country for JE transmission. Up to now, JE cases have been found in at least 29 provinces, with Bali, West Kalimantan, East Nusa Tenggara, West Java and East Java, being the areas of highest incidence. However, routine surveillance on JE has not been established at the national level even though many surveys were conducted. JEV has been isolated from 10 mosquito species: Culex tritaeniorhynchus, Cx. gelidus, Cx. vishnui, Cx. fuscocephala, Cx. bitaeniorhynchus, Cx. quinquefasciatus, Anopheles vagus, An. kochi, An. annularis, and Armigeres subalbatus. Culex tritaeniorhynchus is the main JE vector in Indonesia. JE has been detected throughout the Indonesian archipelago from West to East. However, due to a lack of routine, systematic and standardized diagnostic approaches, the JE burden has still not been clearly established yet. Long term and systematic JE surveillance across Indonesia is a priority, the burden needs to be better assessed and appropriate control measures must be implemented.

Endemic and emerging acute virus infections in Indonesia: an overview of the past decade and implications for the future

Being the largest archipelago country in the world, with a tropical climate and a unique flora and fauna, Indonesia habitats one of the most diverse biome in the world. These characteristics make Indonesia a popular travel destination, with tourism numbers increasing yearly. These characteristics also facilitate the transmission of zoonosis and provide ideal living and breading circumstances for arthropods, known vectors for viral diseases. A review of the past 10 years of literature, reports of the Ministry of Health, Republic of Indonesia and ProMED-mail shows a significant increase in dengue infection incidence. Furthermore, chikungunya, Japanese encephalitis and rabies are proven to be endemic in Indonesia. The combination of cohort studies, governmental data and ProMED-mail reveals an integrated overview for those working in travel medicine and public health, focusing on both endemic and emerging acute virus infections. This review summarizes the epidemiology of acute virus infections in Indonesia, including outbreak reports, as well as public health response measurements and their potential or efficacy. Knowledge about human behaviour, animal reservoirs, climate factors, environment and their role in emerging virus infection are discussed. We aim to support public health authorities and health care policy makers in a One Health approach.

Incubation periods of mosquito-borne viral infections: a systematic review

Mosquito-borne viruses are a major public health threat, but their incubation periods are typically uncited, non-specific, and not based on data. We systematically review the published literature on six mosquito-borne viruses selected for their public health importance: chikungunya, dengue, Japanese encephalitis, Rift Valley fever, West Nile, and yellow fever viruses. For each, we identify the literature's consensus on the incubation period, evaluate the evidence for this consensus, and provide detailed estimates of the incubation period and distribution based on published experimental and observational data. We abstract original data as doubly interval-censored observations. Assuming a log-normal distribution, we estimate the median incubation period, dispersion, 25th and 75th percentiles by maximum likelihood. We include bootstrapped 95% confidence intervals for each estimate. For West Nile and yellow fever viruses, we also estimate the 5th and 95th percentiles of their incubation periods.

Two laboratory-confirmed cases of Japanese encephalitis imported to Germany by travelers returning from Southeast Asia

Japanese encephalitis virus is the leading cause of encephalitis in Asia and parts of the Pacific. Despite the high number of symptomatic infections in endemic countries, clinical disease in travelers is rare. However, an increasing number of imported infections from popular holiday destinations in Southeast Asia have been recorded in the past few years, including serious disease courses in short-term travelers. Here we report two severe, non-fatal cases in tourists, who returned from a long-time stay in Thailand and a short-term trip to Bali, Indonesia, respectively. Recommendations for vaccination and pre-travel advice are discussed.

Japanese encephalitis in travelers from non-endemic countries, 1973-2008

Japanese encephalitis (JE) is a severe disease and a risk for travelers who visit JE-endemic countries. We reviewed all published JE cases in travelers from non-endemic areas from 1973 through 2008, and assessed factors related to risk of infection. There were 55 cases that occurred in citizens of 17 countries. Age range of case-patients was 1-91 years (median = 34 years). Ten (18%) persons died and 24 (44%) had mild to severe sequelae. In a detailed risk assessment of 37 case-patients, 24 (65%) had spent > or = 1 month in JE-endemic areas, and most had factors identified that may have increased infection risk. The estimate of overall JE risk was low, < 1 case/1 million travelers to JE-endemic countries. Nonetheless, for each traveler, a careful assessment of itinerary and activities, a decision on vaccination, and information on mosquito precautions are needed to reduce the risk of this disease.

Immunogenicity and safety of IXIARO (IC51) in a Phase II study in healthy Indian children between 1 and 3 years of age

For adults the standard administration of the Japanese encephalitis vaccine IXIARO is two injections of 6 microg in a 28-day interval. Immunogenicity and safety of 3 and 6 microg of IXIARO compared to JenceVac were investigated in 60 healthy Indian children aged between 1 and 3 years. JE specific neutralizing antibodies were measured at baseline and 28 days after the first and second vaccination. On Day 56 SCR of the 3 and 6 microg IXIARO and the JenceVac group were 95.7%, 95.2% and 90.9%, respectively, and GMT were 201, 218 and 230, respectively, both without statistically significant difference between the three groups. Local and systemic tolerability were captured in a diary 7 days post-vaccination. No apparent difference was seen in the safety profile between the vaccines. These first immunogenicity and safety data in children are promising and support the use of a 3 microg dose in children below the age of three for further development of IXIARO in the paediatric population.

A new inactivated Japanese encephalitis vaccine for adult travelers

Current guidelines for Japanese encephalitis (JE) vaccine relate to an older mouse brain derived vaccine with an uncertain history of adverse events including delayed anaphylaxis. JE is widely distributed, including in urban areas. Underreporting is likely in many endemic countries, and atypical clinical forms exist. A new JE vaccine produced in Vero cells has become available, which appears equi-efficacious to the mouse brain derived vaccine. In development trials the new JE vaccine was as well tolerated as placebo. A review of existing guidelines for JE vaccine use in travelers should be considered.

IC51 Japanese encephalitis vaccine

Japanese encephalitis is the leading cause of viral encephalitis in Asia. Every year 30,000 - 50,000 cases and 10,000 deaths from Japanese encephalitis are reported, and underreporting has been suggested. No effective antiviral therapy exists to treat this mosquito-borne flavivirus infection. For active immunization vaccines are available. The manufacturing of the only vaccine that was internationally licensed, JE-VAX, was ceased in 2005. Therefore a shortage of Japanese encephalitis vaccines might occur before new generation vaccines based on cell culture technology will be available. A promising new vaccine candidate is the inactivated whole-virus vaccine IXIARO (Strain SA(14)-14-2), developed by Intercell AG. Which was licensed in Europe, the USA and Australia in spring 2009. Recently, successful Phase III immunogenicity and tolerability studies were published, indicating that this vaccine will be an acceptable approach to active immunization against Japanese encephalitis. Cell-culture-based vaccines will not only be used in the population living in endemic areas where the risk of infection is high, but also by travelers and military personnel.

Comparison of a single, high-dose vaccination regimen to the standard regimen for the investigational Japanese encephalitis vaccine, IC51: a randomized, observer-blind, controlled Phase 3 study

The standard administration of the investigational Japanese encephalitis vaccine IC51 is 2 doses of 6 microg with a 28-day interval. This study investigated the immunogenicity of a single-immunization, high-dose regimen (1 x 12 microg) compared to the 2-injection, standard regimen to determine the immune response that one, high-dose injection can confer. The single, high-dose regimen resulted in about 60% seroconversion rate (SCR) at 10 days after administration, but it did not reach the almost 100% SCR achieved by the 2-dose standard administration at Day 35. The standard regimen conferred essentially 100% seroconversion already 7 days after the second immunization.

Japanese encephalitis vaccine in travelers

Extensive vaccination against Japanese encephalitis (JE) has been carried out in many Asian countries for the past 20 years and is also increasingly recommended for travelers to endemic areas. Concerns have been raised regarding potential neurological and allergic side effects of the currently available JE vaccine, which is manufactured from mouse brain. A new purified, inactivated JE virus vaccine (IC51) has been developed, which is manufactured in a Vero cell culture substrate. Studies show that the vaccine is both safe and immunogenic and the product will be licensed very soon for use in many industrialized countries. Once a highly immunogenic and safe product is available, wider use of JE vaccine in travelers will be prudent. Currently, vaccination is restricted to travelers with an increased risk of acquiring JE. Individuals at increased risk have been defined quite arbitrarily as travelers with increased behavioral contact to JE-transmitting mosquitoes, in particular, during stays in rural areas and during the transmission season. However, the possibility of an infection with JE virus can never be ruled out when traveling to endemic areas and infection can prove disastrous for the individual concerned. Since a safe product will be available very soon, guidelines and recommendations will have to be reconsidered.

Does antiviral therapy have a role in the control of Japanese encephalitis?

Approximately 2 billion people live in countries where Japanese encephalitis (JE) presents a significant risk to humans and animals, particularly in China and India, with at least 700 million potentially susceptible children. The combined effects of climate change, altered bird migratory patterns, increasing movement of humans, animals and goods, increasing deforestation and development of irrigation projects will inevitably lead to further geographic dispersal of the virus and an enhanced threat. Although most human infections are mild or asymptomatic, some 50% of patients who develop encephalitis suffer permanent neurologic defects, and 25% die. Vaccines have reduced the incidence of JE in some countries. No specific antiviral therapy is currently available. Interferon alpha-2a was tested in a double-blind placebo-controlled trial on children with Japanese encephalitis, but with negative results. There is thus a real need for antivirals that can reduce the toll of death and neurological sequelae resulting from infection with JE virus. Here we briefly review the epidemiological problems presented by this virus, the present state of drug development and the contributory role that antiviral therapy might play in developing future control strategies for JE.

Special infectious disease risks of expatriates and long-term travelers in tropical countries. Part II: infections other than malaria

A wide range of viral, bacterial, and protozoal diseases pose risk to long-term tropical travelers. Risk varies geographically and with lifestyle. For some infections, risk increases with duration of stay, coming to resemble that of the local population. Risk management strategies include vaccination, chemoprophylaxis, avoidance measures, and screening, where appropriate. Vaccination against hepatitis A and B, typhoid, and rabies is recommended for all long-term travelers to (sub-)tropical areas. Lowering of the vaccination threshold for Japanese encephalitis is suggested. Meningococcal disease is rare in travelers, but vaccination is safe and acceptable. The efficacy of Bacillus Calmette-Guérin (BCG) is uncertain; immunological testing avoids BCG's confounding of tuberculin testing. Diarrhea is common, and self-treatment may be recommended. Sexually transmitted infections including human immunodeficiency virus (HIV) are serious risks; education, screening, and HIV postexposure prophylaxis following involuntary exposure are recommended. Many infections are chronic or asymptomatic, and appropriate screening is recommended on return or after prolonged exposure.

A hospital-based surveillance for Japanese encephalitis in Bali, Indonesia

BACKGROUND

Japanese encephalitis (JE) is presumed to be endemic throughout Asia, yet only a few cases have been reported in tropical Asian countries such as Indonesia, Malaysia and the Philippines. To estimate the true disease burden due to JE in this region, we conducted a prospective, hospital-based surveillance with a catchment population of 599,120 children less than 12 years of age in Bali, Indonesia, from July 2001 through December 2003.

METHODS

Balinese children presenting to any health care facility with acute viral encephalitis or aseptic meningitis were enrolled. A "confirmed" diagnosis of JE required the detection of JE virus (JEV)-specific IgM in cerebrospinal fluid, whereas a diagnosis of "probable JE" was assigned to those cases in which JEV-specific IgM was detected only in serum.

RESULTS

In all, 86 confirmed and 4 probable JE cases were identified. The annualized JE incidence rate was 7.1 and adjusted to 8.2 per 100,000 for children less than 10 years of age over the 2.5 consecutive years of study. Only one JE case was found among 96,920 children 10-11 years old (0.4 per 100,000). Nine children (10%) died and 33 (37%) of the survivors had neurological sequelae at discharge. JEV was transmitted in Bali year-round with 70% of cases in the rainy season.

CONCLUSION

JE incidence and case-fatality rates in Bali were comparable to those of other JE-endemic countries of Asia. Our findings contradict the common wisdom that JE is rare in tropical Asia. Hence, the geographical range of endemic JE is broader than previously described. The results of the study support the need to introduce JE vaccination into Bali.

Allergic reactions to Japanese encephalitis vaccine

The JEV widely is used in Asian countries each year and is an important vaccine for travelers to the East from other parts of the world. JE virus is a zoonotic disease with natural reservoirs and cannot be eliminated. Although a declining incidence of JE has been observed in Asia because of reduced transmission by agricultural approaches and vaccination, the most important control measure now, and in the future, is vaccination of humans against JE. The inactivated vaccine, produced from infected mouse-brain-derived tissue, is the only commercially available vaccine. There are several concerns with the use of this vaccine. It is expensive, requires two or three doses to achieve protective efficacy, and, in practice, requires further booster doses to maintain immunity. The apparent increase in allergic reactions in the first part of the 1990s has set focus on the safety of the JEV. A cheap, live attenuated SA 14-14-2 vaccine is used almost exclusively in China and parts of Korea, but there have been no trials of SA 14-14-2 vaccine outside JE endemic countries. The vaccine seems to be highly efficient, and few adverse events have been observed; however, PHK cells are used for the production of this vaccine, and these cells are not approved by the WHO. A satisfactory cell substrate is needed. A committee under the WHO has proposed that for the live JEV, there should be validity of the assays for retrovirus when applied to PHK cell substrate and validity of the mouse assays for neurovirulence. Further information should be reviewed on the long-term follow-up of recipients of the vaccine. Several new types of vaccines have reached the phase of clinical trials; however, studies remain to be completed. Until a new vaccine is available, the priority of surveillance of adverse events and the continuous reporting of such events to the users of the vaccines must be of importance. This fact is highlighted by the possibility of the varying frequency of adverse events with different batches over the years. The WHO offers information and recommendations for vaccines in the EPI and issues a series of updated papers on other vaccines that are of international public health importance (eg, JEV). The development of alternative efficient, safe, and appropriately priced JEVs is recommended, as is intensified surveillance of adverse events. Prospective vaccine studies of safety may be limited because of sample size and because rare adverse events may not be detected. Several new initiatives have been taken to improve surveillance of adverse events to vaccines within the past 10 years. In Japan, there is an increasing awareness of the importance of efforts taken to improve vaccine safety, and surveillance of adverse events and possibilities of compensation for vaccine-related injuries are in place. In Vietnam, a database to detect adverse events after vaccination has been established; the project involves active visits to data collectors at the vaccination sites. Comparative studies of adverse events, such as one recent study from Japan and the United States, are important for the evaluation of the reporting systems. The reporting rate for JEV adverse events from Japan was approximately one order of magnitude lower than that in the United States. Japan had strict predefined reporting criteria and time limits for observations. If time limits for the observation are too strict (eg, defining a possible neurologic reaction to occur within 1 week after vaccination), later reactions will not be included (eg, if ADEM is elicited by a vaccine, the symptoms cannot be expected to occur until weeks after the vaccination). The passive surveillance systems have limitations with an underreporting of adverse events, depending on clinical seriousness, temporal proximity to vaccination, awareness of healthcare workers, and tradition of reporting particular events. In developed countries, surveillance of adverse events is formalized, although not necessarily optimal. An increase in reporting would be expected when the reporting of adverse events is mandatory. Reports have been sent to VAERS, the Vaccine Safety Datalink Project, and the European Union Pharmacovigilance System. A Brighton collaboration has been implemented to enhance comparability of vaccine safety data. Public health authorities in specific countries, such as the CDC in the United States and the National Advisory Committee in Canada, regularly have published information on the JE situation in Asia and the preventive measures to be taken, including information on the vaccines and adverse reactions. The conventional recommendation is that travelers should be vaccinated if they will spend more than 1 month in a JE endemic area or in areas with epidemic transmission with even shorter periods. Although the risk for JE for short-term travelers is considered small (1 case per 1 million travelers per year), sporadic cases, including deaths, have been reported among tourists traveling to endemic areas. Risk for travelers in rural districts in the season of risk is considerably higher (range, 1 case per 5000 travelers to 1 case per 20,000 travelers per week). Doctors who advise travelers should be updated on the latest JE occurrences in Asia. Updates on the JE situation can be found on bulletins at http://www.promedmail.org or are available from the WHO or CDC. The allergic reactions primarily described after vaccination with the inactivated mouse-brain-derived JEV have been observed in several countries during the 1900s. Allergic reactions, including the mucocutaneous and neurologic reactions reported after JE vaccination, may vary in frequency, and these reactions should be evaluated meticulously yearly. This step enables recommendations, including information on possible side effects, to be given in an optimal way.

Vaccination priorities

Selection of immunizations should be based on requirements and on risk of infection. According to the International Health Regulations, many countries require yellow fever vaccination and proof thereof as the International Certificate of vaccination. Additionally selected countries require proof of vaccination against cholera and meningococcal disease. A consultation for travel health advice is always an opportunity to ascertain that routine immunizations have been performed. Recommended immunizations often are more important for traveller's health than the required or routine ones. The most frequent vaccine preventable infection in non-immune travellers to developing countries is hepatitis A with an average incidence rate of 0.3% per month; in high risk backpackers or foreign-aid-volunteers this rate is 2.0%. Many immunizations are recommended for special risk groups only: there is a growing tendency in many countries to immunize all young travellers to developing countries against hepatitis B, as it is uncertain who will voluntarily or involuntarily get exposed. The attack rate of influenza in intercontinental travel is estimated to be 1%. Immunity against poliomyelitis remains essential for travel to Africa and parts of Asia. Many of the 0.2-0.4% who experience an animal bite are at risk of rabies. Typhoid fever is diagnosed with an incidence rate of 0.03% per month among travellers to the Indian subcontinent, North and West Africa (except Tunisia), and Peru, elsewhere this rate is 10-fold lower. Meningococcal disease, Japanese encephalitis, cholera and tuberculosis have been reported in travellers, but these infections are rare in this population. Although no travel health vaccine is cost beneficial, most professionals will offer protection against the frequent risks, while most would find it ridiculous to use all available vaccines in every traveller. It is essentially an arbitrary decision made on the risk level one wishes to recommend protection--but the priorities need to be set correctly.

Immunizations for international travel

Many infections encountered by international travelers can be prevented by adherence to personal protective measures and appropriate vaccinations. This review outlined the incidence and importance of the major vaccine-preventable infectious diseases encountered by U.S. travelers, as well as the indications, contraindications, and side effects of available vaccines. Official proof of yellow fever vaccine often is required for entry into some countries. Based on endemic or epidemic infections at destinations, planned activities, and age and medical history of international travelers, other vaccines may be recommended. Many clinicians will be familiar with some of the infections and vaccines that may be used in travelers; other vaccines may be encountered infrequently and associated with significant risk of adverse effects. Since vaccines do not provide complete protection and some travel-related infections do not have vaccines available yet (e.g., malaria and dengue fever), physicians need to be vigilant concerning febrile illness in returning travelers.

Japanese encephalitis vaccine for travelers: exploring the limits of risk

The prevention of Japanese encephalitis in travelers presents the juxtaposition of 4 factors: a disease that is widespread throughout Asia, a disease with a low incidence in travelers, a vaccine about which there are safety concerns, and a clinical course that can result in death or permanent disability in two-thirds of symptomatic cases. Travel medicine practitioners often seem to be polarized into 2 groups: a group that gives more weight to the severity of the disease (and therefore often recommend vaccination) and another group that is more persuaded by the low occurrence of cases in travelers (and therefore rarely recommend vaccination). This review assesses the known risks of contracting Japanese encephalitis and the risks associated with the vaccine and tries to develop an appropriate way to recommend this vaccine to travelers who may be at significant risk.

Adverse events after Japanese encephalitis vaccination: review of post-marketing surveillance data from Japan and the United States. The VAERS Working Group

We determined the reporting rates for adverse events following the administration of inactivated mouse-brain derived Japanese encephalitis vaccine (JEV) based on post-marketing surveillance data from Japan and the United States. The rate of total adverse events per 100,000 doses was 2.8 in Japan and 15.0 in the United States. In Japan, 17 neurological disorders were reported from April 1996 to October 1998 for a rate of 0.2 per 100,000 doses. In the United States, no serious neurological adverse events temporally associated with JEV were reported from January 1993 to June 1999. Rates for systemic hypersensitivity reactions were 0.8 and 6.3 per 100,000 doses in Japan and the United States, respectively. Passively collected VAERS surveillance data indicate that characteristic hypersensitivity reactions with a delayed onset continue to occur among JEV recipients and that conservative recommendations limiting its use to travelers at high risk of infection with Japanese encephalitis are appropriate.

Antibodies to Japanese encephalitis virus in human sera collected from Irian Jaya. Follow-up of a previously reported case of Japanese encephalitis in that region

Japanese encephalitis virus (JEV) and other arboviruses are demonstrating an emergence in the southern part of New Guinea Island. JE was previously unknown in this part of the world until 1995 when it was found in the Torres Strait, northern Australia. In this study 96 sera collected from residents of the Timika region of Irian Jaya were tested for antibodies to JEV and related arboviruses by epitope-specific blocking ELISA. Of the 9 sera deemed to be positive for JEV antibodies by ELISA, 5 were collected from persons indigenous to Timika, and who had not travelled to regions where JE is known to be active. This indicates that these individuals were infected with JEV in the Timika area and supports a recent report of a clinical case of JE in this region. Non-immune expatriates visiting or working in the Lowland areas of Irian Jaya and/or Papua New Guinea should consider immunization against JE. Precautions should always be taken to avoid being bitten by any mosquito both in the daytime and at night.

Japanese encephalitis

Japanese encephalitis (JE) is an acute encephalomyelitis which is a primary viral encephalitis accompanying a viral infection. Clinically, the patient who either resides in an endemic region or who has been exposed to the viral vector (mosquito) may have symptoms including high fever, headache, and impaired consciousness. JE involves many portions of the supratentorial and infratentorial compartments including the brain stem, hippocampus, thalamus, basal ganglia, and white matter. Classically MR imaging demonstrates the lesions of JE as hyperintense on T2-weighted images and hypointense on T1-weighted images. Hemorrhagic transformations have also been described in JE lesions, with corresponding expected T1 and T2 changes. Differential considerations based on the MRI appearance are somewhat broad, including but not limited to primary viral encephalitis, acute encephalopathy, limbic encephalitis, and acute disseminated encephalomyelitis. The therapy for JE is primarily conservative and supportive since there is no specific treatment for JE, and the disease has a high fatality rate. The prognosis depends on the extent of involvement at primary presentation, and on the autoimmune mechanisms of this disease.

Japanese Encephalitis in Western Irian Jaya

Japanese encephalitis (JE) is one of the emerging infectious diseases now widespread in Asia, with recent extension into Torres Strait in northern Australia.1,2 In Indonesia, JE was not considered to be a serious clinical problem,3 although seroprevalence studies showed high prevalence of JE-neutralizing antibody in residents of Java, Kalimantan, Bali, with low prevalence in Sulawesi, Maluka and Irian Jaya.4 Confirmed clinical cases of JE have been rare in Indonesia and mainly have been reported in the west,3 and in tourists visiting Bali.5 No clinical cases of JE have been reported from Irian Jaya. This paper describes a clinical case of JE in a child from Irian Jaya and its confirmation by serology.

Japanese encephalitis vaccine in travellers. Is wider use prudent?

Vaccination against Japanese encephalitis has been carried out extensively in many Asian countries for the past 20 years and is also increasingly recommended for travellers to endemic areas. Although the currently available vaccine, manufactured from mouse brain, is generally considered to be highly effective and of low reactogenicity, approximately 50% of vaccinees report experiencing usually mild adverse effects following vaccination. Concern has been raised regarding potential neurological adverse effects but the incidence of such effects appears to be very low (around 1 to 2.3 per 1000000 vaccinations). Routine vaccination of all travellers to endemic areas is clearly not beneficial at this moment and use of the vaccine should remain restricted to persons spending a month or longer in endemic areas, especially rural areas, during the transmission season. However, when counselling individual travellers, it has to be kept in mind that the possibility of Japanese encephalitis can never be ruled out completely when travelling to endemic areas, and that such an infection can prove disastrous for the individual concerned.

Adverse reactions to Japanese encephalitis vaccine in travellers

Vaccination against Japanese Encephalitis (JE) has been carried out extensively in many Asian countries for the past 20 years. The vaccine was generally considered to be effective and of low reactogenity. However, since 1989 an unusual number of systemic reactions characterized mainly by generalized urticaria and/or angioedema following JE vaccination were reported from Australia, Canada and Denmark, 860 travellers were recruited during a period of 16 months for a prospective study with the aim to investigate the type and incidence of side effects following JE vaccination (JEV) in German travellers. 826 received a primary immunization (2 injections at days 0 and 7-14) and 34 received a single booster injection. A detailed standardized questionnaire was distributed to all vaccinees after the first injection. A total of 509 questionnaires could be evaluated, which represents a return rate of 59.2%. 46% of the vaccinees reported about no adverse events at all. 54% reported about one or more adverse effects. Local reactions at the injection site were observed by 209 vaccinees, while 65 reported about systemic side effects like headache, fever, dizziness and generalized rash. There was no significant difference following first or second injection of the primary immunization or the booster injection, respectively, regarding incidence, severity or type of side effects. 2.2% of the vaccinees reporting reactions sought medical advice and 1.8% were judged unfit for work for an average of 2.2 days. The amount of systemic reactions might indicate a potential hazard of serious anaphylactic reactions. Unlike hepatitis A. Japanese encephalitis is an extremely rare disease in travellers. Therefore, the risk of acquiring the disease when travelling to affected areas without prior immunization should be considered against the risk of developing serious side effects after vaccination. We conclude that JEV should remain restricted to travellers with an increased risk of acquiring JE.

Imported vector- and rodent-borne virus infections--an introduction

Travel is a potent force in the emergence of virus infections. Migration of humans and animals has been the pathway for disseminating virus diseases throughout history. In recent years, dengue virus has been identified as the most important travel-related, vector-borne virus disease. Other vector-borne virus infections, such as sandfly fever, Rift Valley fever, chikungunya fever and Japanese encephalitis, have been diagnosed in travelers returning from endemic areas. Crimean-Congo haemorrhagic fever may not only be imported by infected live stock, but also by travelers. Of rodent-borne virus infections, Lassa fever has been diagnosed occasionally in travelers returning from endemic areas. The potential impact of imported filoviruses is currently discussed.