Seasonality, annual trends, and characteristics of dengue among ill returned travelers, 1997-2006

A cluster of dengue cases in American missionaries returning from Haiti, 2010

Dengue is an acute febrile illness caused by four mosquito-borne dengue viruses (DENV-1 to -4) that are endemic throughout the tropics. After returning from a 1-week missionary trip to Haiti in October of 2010, 5 of 28 (18%) travelers were hospitalized for dengue-like illness. All travelers were invited to submit serum specimens and complete questionnaires on pre-travel preparations, mosquito avoidance practices, and activities during travel. DENV infection was confirmed in seven (25%) travelers, including all travelers that were hospitalized. Viral sequencing revealed closest homology to a 2007 DENV-1 isolate from the Dominican Republic. Although most (88%) travelers had a pre-travel healthcare visit, only one-quarter knew that dengue is a risk in Haiti, and one-quarter regularly used insect repellent. This report confirms recent DENV transmission in Haiti. Travelers to DENV-endemic areas should receive dengue education during pre-travel health consultations, follow mosquito avoidance recommendations, and seek medical care for febrile illness during or after travel.

Vaccination of travelers: how far have we come and where are we going?

Vaccine recommendations are a prominent part of health preparations before international travel. We review progress made in the past decade regarding vaccines used primarily by persons traveling from high-income countries to low- and middle-income countries. The combined hepatitis A-B vaccine, the recently licensed Vero cell-derived Japanese encephalitis vaccine and conjugated quadrivalent meningococcal vaccines are discussed. This article provides updates on yellow fever vaccine-associated visceral and neurologic adverse events, indications for influenza vaccine in travelers, the rapid immunization schedule for tick-borne encephalitis vaccine, schedules for postexposure rabies prophylaxis, and new insights about oral cholera vaccines following the outbreak in Haiti. The future should bring vaccines for serogroup B Neiserria meningitidis, dengue and malaria, as well as an inactivated yellow fever vaccine.

Spatial patterns and socioecological drivers of dengue fever transmission in Queensland, Australia

BACKGROUND

Understanding how socioecological factors affect the transmission of dengue fever (DF) may help to develop an early warning system of DF.

OBJECTIVES

We examined the impact of socioecological factors on the transmission of DF and assessed potential predictors of locally acquired and overseas-acquired cases of DF in Queensland, Australia.

METHODS

We obtained data from Queensland Health on the numbers of notified DF cases by local government area (LGA) in Queensland for the period 1 January 2002 through 31 December 2005. Data on weather and the socioeconomic index were obtained from the Australian Bureau of Meteorology and the Australian Bureau of Statistics, respectively. A Bayesian spatial conditional autoregressive model was fitted at the LGA level to quantify the relationship between DF and socioecological factors.

RESULTS

Our estimates suggest an increase in locally acquired DF of 6% [95% credible interval (CI): 2%, 11%] and 61% (95% CI: 2%, 241%) in association with a 1-mm increase in average monthly rainfall and a 1°C increase in average monthly maximum temperature between 2002 and 2005, respectively. By contrast, overseas-acquired DF cases increased by 1% (95% CI: 0%, 3%) and by 1% (95% CI: 0%, 2%) in association with a 1-mm increase in average monthly rainfall and a 1-unit increase in average socioeconomic index, respectively.

CONCLUSIONS

Socioecological factors appear to influence the transmission of DF in Queensland, but the drivers of locally acquired and overseas-acquired DF may differ. DF risk is spatially clustered with different patterns for locally acquired and overseas-acquired cases.

Internally controlled, generic real-time PCR for quantification and multiplex real-time PCR with serotype-specific probes for serotyping of dengue virus infections

Dengue has become a global public health problem and a sensitive diagnostic test for early phase detection can be life saving. An internally controlled, generic real-time PCR was developed and validated by testing serial dilutions of a DENV positive control RNA in the presence of a fixed amount of IC with results showing a good linearity (R² = 0.9967) and a LOD of at least 1.95 × 10⁴ copies/mL. Application of the generic PCR on 136 patient samples revealed a sensitivity of 95.8% and specificity of 100%. A newly developed multiplex real-time PCR with serotype-specific probes allowed the serotyping of DENV for 80 out of 92 (87%) generic real-time PCR positive patients. Combined these real-time PCRs offer a convenient diagnostic tool for the sensitive and specific quantification of DENV in clinical specimens with the possibility for serotyping.

Health recommendations for international travel: a review of the evidence base of travel medicine

PURPOSE OF REVIEW

International travel is increasing, including travel to countries with emerging economies. Travel may pose health risks for the individual and contribute to the global spread of infectious diseases. The specialty of travel medicine is aimed at minimizing health risks associated with international travel. The field has emerged in the past 25 years, and the evidence base supporting its clinical practice is growing. This review will describe the evidence base underlying travel medicine, highlight recently updated travel medicine guidelines, and outline future research priorities.

RECENT FINDINGS

Recommendations for a number of common vaccines for travelers have been updated recently. More sophisticated detection methods are leading to the identification of a wider spectrum of pathogens associated with travelers' diarrhea, and antibiotic resistance is increasingly being identified. New treatment options for malaria are available, and a fifth Plasmodium species causing disease in humans has been identified.

SUMMARY

An evidence base for the practice of travel medicine is emerging. Expert opinion and consensus guidelines continue to play an important role in supporting clinical practice.

Meteorological factors and El Niño Southern Oscillation are independently associated with dengue infections

Our objective was to determine the association between temperature, humidity, rainfall and dengue activity in Singapore, after taking into account lag periods as well as long-term climate variability such as the El Niño Southern Oscillation Index (SOI). We used a Poisson model which allowed for autocorrelation and overdispersion in the data. We found weekly mean temperature and mean relative humidity as well as SOI to be significantly and independently associated with dengue notifications. There was an interaction effect by periods of dengue outbreaks, but periods where El Niño was present did not moderate the relationship between humidity and temperature with dengue notifications. Our results help to understand the temporal trends of dengue in Singapore, and further reinforce the findings that meteorological factors are important in the epidemiology of dengue.

Travel-related dengue virus infection, The Netherlands, 2006-2007

To assess the incidence of and risk factors for clinical and subclinical dengue virus (DENV) infection, we prospectively studied 1,207 adult short-term travelers from the Netherlands to dengue-endemic areas. Participants donated blood samples for serologic testing before and after travel. Blood samples were tested for antibodies against DENV. Seroconversion occurred in 14 (1.2%) travelers at risk. The incidence rate was 14.6 per 1,000 person-months. The incidence rate was significantly higher for travel during the rainy months. Dengue-like illness occurred in 5 of the 14 travelers who seroconverted. Seroconversion was significantly related to fever, retro-orbital pain, myalgia, arthralgia, and skin rash. The risk for DENV infection for short-term travelers to dengue-endemic areas is substantial. The incidence rate for this study is comparable with that in 2 other serology-based prospective studies conducted in the 1990s.

Cases of travel-acquired dengue fever in Denmark 2001-2009

Dengue fever (DF) remains one of the most important emerging infectious diseases. Whereas DF is well recognized in endemic countries, there are indications that the disease is underdiagnosed among travellers to endemic regions. Here, we present the first descriptive survey on cases of travel-acquired DF imported to Denmark diagnosed at the national reference laboratory for dengue virus diagnostics during a 9-year period. In our study, 16 - 46 travel-acquired dengue virus infections were diagnosed per year. DF is mainly imported by adults, mostly men, returning from Southeast Asian countries. The minimum incidence of dengue virus infection among Danish travellers is estimated to be 4.9 per 100,000 travellers. Our results confirm and expand studies from other European countries, and underline the importance of surveillance based on relevant diagnostic analyses.

The early clinical features of dengue in adults: challenges for early clinical diagnosis

BACKGROUND

The emergence of dengue throughout the tropical world is affecting an increasing proportion of adult cases. The clinical features of dengue in different age groups have not been well examined, especially in the context of early clinical diagnosis.

METHODOLOGY/PRINCIPAL FINDINGS

We structured a prospective study of adults (≥ 18 years of age) presenting with acute febrile illness within 72 hours from illness onset upon informed consent. Patients were followed up over a 3-4 week period to determine the clinical outcome. A total of 2,129 adults were enrolled in the study, of which 250 (11.7%) had dengue. Differences in the rates of dengue-associated symptoms resulted in high sensitivities when the WHO 1997 or 2009 classification schemes for probable dengue fever were applied to the cohort. However, when the cases were stratified into age groups, fewer older adults reported symptoms such as myalgia, arthralgia, retro-orbital pain and mucosal bleeding, resulting in reduced sensitivity of the WHO classification schemes. On the other hand, the risks of severe dengue and hospitalization were not diminished in older adults, indicating that this group of patients can benefit from early diagnosis, especially when an antiviral drug becomes available. Our data also suggests that older adults who present with fever and leukopenia should be tested for dengue, even in the absence of other symptoms.

CONCLUSION

Early clinical diagnosis based on previously defined symptoms that are associated with dengue, even when used in the schematics of both the WHO 1997 and 2009 classifications, is difficult in older adults.

Dengue and chikungunya infections in travelers

PURPOSE OF REVIEW

Dengue and chikungunya are arboviruses that have caused major outbreaks and infected travelers, and both can be associated with fever and rash. We review the recent epidemiology of dengue and chikungunya infections and discuss their clinical presentations, diagnosis, treatment, and prevention. We highlight the findings in travelers.

RECENT FINDINGS

Globally dengue is one of the most common infections associated with travel, and incidence has increased in the Americas in recent years, especially in Brazil. Chikungunya has caused dramatic outbreaks in the Indian Ocean islands since 2004, and has spread to south and south-east Asia. Dengue virus and chikungunya virus also possess the potential to cause autochthonous transmission in temperate regions of developed countries due to the presence of the vector mosquito, Aedes albopictus. Such an outbreak (chikungunya infection) did occur in 2007 in Italy. A mutation in chikungunya virus (A226V) appears to improve virus survival in Aedes albopictus and also increase its virulence.

SUMMARY

The findings assist in differentiating dengue and chikungunya from other acute febrile illnesses and from each other. The findings also illustrate potential outbreaks in nonendemic countries, important toward developing control and prevention strategies.

Pediatric travelers visiting friends and relatives (VFR) abroad: illnesses, barriers and pre-travel recommendations

Global mobility has shown a steady rise in recent years, with increased immigration and international travel. The VFR traveler is a traveler whose primary purpose of travel is to visit friends and relatives (VFR), where there is a gradient of risk between home and destination. Children are more likely to be VFR travelers than adults. Pediatric VFR travelers have higher risks for certain infectious travel-related illnesses and face multiple barriers in receiving comprehensive pre-travel care. This review focuses on the current state of knowledge of the pediatric VFR traveler, including epidemiological risks, barriers to adequate pre-travel services, and specific recommendations for disease prevention.

The role of imported cases and favorable meteorological conditions in the onset of dengue epidemics

Background

Travelers who acquire dengue infection are often routes for virus transmission to other regions. Nevertheless, the interplay between infected travelers, climate, vectors, and indigenous dengue incidence remains unclear. The role of foreign-origin cases on local dengue epidemics thus has been largely neglected by research. This study investigated the effect of both imported dengue and local meteorological factors on the occurrence of indigenous dengue in Taiwan.

Methods and Principal Findings

Using logistic and Poisson regression models, we analyzed bi-weekly, laboratory-confirmed dengue cases at their onset dates of illness from 1998 to 2007 to identify correlations between indigenous dengue and imported dengue cases (in the context of local meteorological factors) across different time lags. Our results revealed that the occurrence of indigenous dengue was significantly correlated with temporally-lagged cases of imported dengue (2–14 weeks), higher temperatures (6–14 weeks), and lower relative humidity (6–20 weeks). In addition, imported and indigenous dengue cases had a significant quantitative relationship in the onset of local epidemics. However, this relationship became less significant once indigenous epidemics progressed past the initial stage.

Conclusions

These findings imply that imported dengue cases are able to initiate indigenous epidemics when appropriate weather conditions are present. Early detection and case management of imported cases through rapid diagnosis may avert large-scale epidemics of dengue/dengue hemorrhagic fever. The deployment of an early-warning surveillance system, with the capacity to integrate meteorological data, will be an invaluable tool for successful prevention and control of dengue, particularly in non-endemic countries.

Dengue/dengue hemorrhagic fever is the world's most widely spread mosquito-borne arboviral disease and threatens more than two-thirds of the world's population. Cases are mainly distributed in tropical and subtropical areas in accordance with vector habitats for Aedes aegypti and Ae. albopictus. However, the role of imported cases and favorable meteorological conditions has not yet been quantitatively assessed. This study verified the correlation between the occurrence of indigenous dengue and imported cases in the context of weather variables (temperature, rainfall, relative humidity, etc.) for different time lags in southern Taiwan. Our findings imply that imported cases have a role in igniting indigenous outbreaks, in non-endemics areas, when favorable weather conditions are present. This relationship becomes insignificant in the late phase of local dengue epidemics. Therefore, early detection and case management of imported cases through timely surveillance and rapid laboratory-diagnosis may avert large scale epidemics of dengue/dengue hemorrhagic fever. An early-warning surveillance system integrating meteorological data will be an invaluable tool for successful prevention and control of dengue, particularly in non-endemic countries.

Two cases of Old World cutaneous leishmaniasis in Australian travelers visiting Morocco

Two cases of Old World cutaneous leishmaniasis (OWCL) acquired by travelers to Morocco are described. In Australia, OWCL is more frequently seen in migrants rather than returned travelers. The patients were treated with sodium stibogluconate and fluconazole. Optimal treatment is not established, particularly in returned travelers, but identification of Leishmania species can help with the selection of appropriate therapy.

Travelers as a sentinel population: use of sentinel networks to inform pretravel and posttravel evaluation

The establishment of collaborative sentinel surveillance networks specifically to monitor disease trends among travelers offers new options for evaluating travel health issues. These networks can inform pre- and posttravel patient management by providing complementary surveillance information, facilitating communication and collaboration between participating network sites, and enabling new analytical options for travel-related research. The two major multinational sentinel networks are TropNetEurop and GeoSentinel. Practical examples demonstrating their significant contributions to improved travel health information are discussed. Data obtained from studying health problems among travelers may also have significant benefits for local populations in resource-limited countries. However, there are limitations of data collected by sentinel networks, so they should be considered as complementary tools and not relied on as an exclusive basis for evaluating health risks among travelers.

Spatial analysis of notified dengue fever infections

This study aimed to investigate the spatial clustering and dynamic dispersion of dengue incidence in Queensland, Australia. We used Moran's I statistic to assess the spatial autocorrelation of reported dengue cases. Spatial empirical Bayes smoothing estimates were used to display the spatial distribution of dengue in postal areas throughout Queensland. Local indicators of spatial association (LISA) maps and logistic regression models were used to identify spatial clusters and examine the spatio-temporal patterns of the spread of dengue. The results indicate that the spatial distribution of dengue was clustered during each of the three periods of 1993-1996, 1997-2000 and 2001-2004. The high-incidence clusters of dengue were primarily concentrated in the north of Queensland and low-incidence clusters occurred in the south-east of Queensland. The study concludes that the geographical range of notified dengue cases has significantly expanded in Queensland over recent years.

Multicenter EuroTravNet/GeoSentinel study of travel-related infectious diseases in Europe

We analyzed prospective data on 17,228 European patients who sought treatment at GeoSentinel sites from 1997 to 2007. Gastrointestinal illness (particularly in tourists), fever (those visiting friends and relatives [VFRs]), and skin disorders (in tourists) were the most common reasons for seeking medical care. Diagnoses varied by country of origin, region visited, or categories of travelers. VFRs who returned from sub-Saharan Africa and Indian Ocean islands were more likely to experience falciparum malaria than any other group. Multiple correspondence analysis identified Italian, French, and Swiss VFRs and expatriate travelers to sub-Saharan Africa and Indian Ocean Islands as most likely to exhibit febrile illnesses. German tourists to Southeast and south-central Asia were most likely to seek treatment for acute diarrhea. Non-European travelers (12,663 patients from other industrialized countries) were less likely to acquire certain travel-associated infectious diseases. These results should be considered in the practice of travel medicine and development of health recommendations for European travelers.

Defining infections in international travellers through the GeoSentinel surveillance network

International travellers are often exposed to a wide range of infections, most of which are a reflection of common diseases in the destination country. The consequences of acquiring such infections are serious and can be associated with substantial morbidity and mortality. Attempting to define the range of infections and the risk factors that are associated with acquiring them during travel to different regions worldwide will provide an evidence base for the development and implementation of effective preventative interventions. This Science and Society article focuses on the valuable function served by the GeoSentinel surveillance network in defining the range of infections in travellers.

Global spread of epidemic dengue: the influence of environmental change

Dengue/dengue hemorrhagic fever is the most important vector-borne viral disease globally, with over half of the world’s population living in areas at risk of infection. Frequent and cyclical epidemics are reported throughout the tropical world, with regular importation of the virus via viremic travelers into both endemic and nonendemic countries. These events coincide with the recently observed global warming that is associated with climate change. Whether these events are coincidental is examined in this article. The history of dengue emergence is traced to determine the major drivers responsible for the spread of both the viruses and mosquito vectors to new geographic regions. We conclude that demographic- and anthropogenic-driven environmental changes, combined with globalization and inefficient public health measures rather than climate change, are the principal driving forces for the re-emergence and spread of epidemic dengue in the past 40 years. These trends are likely to continue given the global trends projected by the United Nations.

A travel medicine view of dengue and dengue hemorrhagic fever

Dengue fever is the most prevalent arboviral infection worldwide, with up to 40% of the world population living in endemic regions. Among travelers to tropical countries, dengue infection is increasingly reported, and it is now a leading cause of post-travel fever. Outbreaks of dengue-like illness were already described since the 18th century, but it is only in the last half century that a severe form of the disease - dengue hemorrhagic fever (DHF) has been described. Although the cause of DHF is not established, the prevailing theory attributes the disease to antibody-dependent enhancement of viral replication, in the presence of a secondary dengue infection. Comparative studies of primary vs. secondary infection are difficult to perform in endemic countries because of the rarity of primary infection except during early infancy. Travelers on the other hand are usually diagnosed with primary infection and are therefore a better study population. Data on dengue and DHF among travelers appears to suggest that severe dengue and DHF occur in similar rates among cases with primary and with secondary infections. Epidemiological and physiological data from travelers suggest that the prevailing theory on the causes of DHF needs to be reconsidered.

Risk estimates of dengue in travelers to dengue endemic areas using mathematical models

BACKGROUND

Dengue has emerged as a frequent problem in international travelers. The risk depends on destination, duration, and season of travel. However, data to quantify the true risk for travelers to acquire dengue are lacking.

METHODS

We used mathematical models to estimate the risk of nonimmune persons to acquire dengue when traveling to Singapore. From the force of infection, we calculated the risk of dengue dependent on duration of stay and season of arrival.

RESULTS

Our data highlight that the risk for nonimmune travelers to acquire dengue in Singapore is substantial but varies greatly with seasons and epidemic cycles. For instance, for a traveler who stays in Singapore for 1 week during the high dengue season in 2005, the risk of acquiring dengue was 0.17%, but it was only 0.00423% during the low season in a nonepidemic year such as 2002.

DISCUSSION

Risk estimates based on mathematical modeling will help the travel medicine provider give better evidence-based advice for travelers to dengue endemic countries.

[Vaccines for the future]

The field of vaccines and vaccinology has seen remarkable progress during the past 20 years. Many vaccines, however, still need to be improved, either because the protection they provide is relatively short-lived and would greatly benefit from the development of booster formulations (as is the case for tuberculosis), or because they only cover part of the many serotypes of the pathogen that causes the disease (rotaviruses, papillomaviruses, or Streptococcus pneumoniae). In addition, still many diseases lack a proper preventive vaccine, such as AIDS, hepatitis C, malaria, viral pneumonias, croup and bronchiolitis, dengue fever, leishmaniasis, Staphylococcus aureus, groups A and B Streptococcus, Shigellas and enterotoxigenic Escherichia coli, to only name a few. These are the current targets of vaccines under development, a great many of which will hopefully reach the market within the coming 10 years. The development of preventive vaccines against chronic diseases such as AIDS and hepatitis C will probably require more time, due to basic science complexities to be overcome first. It is likely that the future will also see an emphasis on therapeutic vaccines targeted against noninfectious diseases such as cancers (lung, skin, prostate, etc) and metabolic or neurologic diseases (atherosclerosis, Alzheimer's disease). This review will focus on examples of preventive vaccines under development that target infectious diseases with a heavy global burden on public health.

The role of the traveler in emerging infections and magnitude of travel

Travel and trade have grown immensely. Travelers interact with people and microbes during their journeys, and can introduce infectious agents to new areas and populations. Studying illnesses in travelers is a source of knowledge into diseases of resource-poor regions and the control of these diseases. Travel-associated illnesses also serve to detect emerging infections.

Geographic expansion of dengue: the impact of international travel

Dengue has emerged as an international public health problem. Reasons for the resurgence of dengue in the tropics and subtropics are complex and include unprecedented urbanization with substandard living conditions, lack of vector control, virus evolution, and international travel. Of all these factors, urbanization has probably had the most impact on the amplification of dengue within a given country, and travel has had the most impact for the spread of dengue from country to country and continent to continent. Epidemics of dengue, their seasonality, and oscillations over time are reflected by the epidemiology of dengue in travelers. Sentinel surveillance of travelers could augment existing national public health surveillance systems.