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Dengue fever continues to spread globally, causing major epidemics and putting major strain on health systems in affected countries. For imported dengue in Europe, south east Asia is the most important region of origin, followed by Latin America, the Indian subcontinent, the Caribbean, and Africa. Information regarding mosquito protective measures is highly recommended for all travellers to affected areas.

Background: Dengue fever is the most common arboviral disease in travelers. In countries where dengue virus is endemic, sequential (secondary) infections with different dengue virus serotypes are associated with disease severity. Data on severity and secondary infection rates in a population of travelers are lacking., Methods: Intensified surveillance of dengue fever in travelers was performed within the European Network on Surveillance of Imported Infectious Diseases. Data were collected at 14 European clinical referral centers between 2003 and 2005., Results: A total of 219 dengue virus infections imported from various regions of endemicity were reported. Serological analysis revealed a secondary immune response in 17%. Spontaneous bleeding was observed in 17 (8%) patients and was associated with increased serum alanine and aspartate aminotransferase levels and lower median platelet counts. Two (0.9%) patients fulfilled the World Health Organization (WHO) case definition for dengue hemorrhagic fever. However, 23 (11%) travelers had severe clinical manifestations (internal hemorrhage, plasma leakage, shock, or marked thrombocytopenia). A secondary immune response was significantly associated with both spontaneous bleeding and other severe clinical manifestations., Conclusions: In travelers, severe dengue virus infections are not uncommon but may be missed if the WHO classification is strictly applied. High liver enzyme levels and low platelet counts could serve as indicators of disease severity.

Background: Several enzyme-linked immunosorbent assay (ELISA)-kits are commercially available for the rapid diagnosis of dengue infection, and have demonstrated good sensitivity and specificity in paired serum samples. In practice, however, often only one blood sample is available from febrile travellers returning from dengue endemic areas., Methods: To evaluate the diagnostic value of positive dengue antibody-titres performed by a standard ELISA (PanBio IgM- and IgG-ELISA) in single serum samples (regarded as "probable infection"), 127 positive samples were further analyzed using envelope/membrane IgM-, and nonstructural protein 1 IgM- and IgG-ELISAs, immunofluorescence assays, and real-time reverse transcription polymerase chain reaction assays (RT-PCR). A combination of the test-results served as the diagnostic "gold standard". A total of 1,035 febrile travellers returning from dengue-endemic countries with negative dengue-serology and RT-PCR served as controls to compare clinical and haematological features., Results: Overall, only 64 (positive predictive value = 50%) of the probable cases were confirmed by additional analysis and 54 (42.5%) were confirmed to be "false-positive". Rash was the only clinical feature significantly associated with confirmed dengue fever. The combination of thrombocytopenia and leucopenia was present in 40.4% of confirmed and in 6.1% of false-positive cases. Thus, the positive predictive value for the combination of positive PanBio-ELISA plus the two haematological features was 90.5%., Conclusion: The examination of paired serum samples is considered the most reliable serodiagnostic procedure for dengue. However, if only one blood sample is available, a single positive ELISA-result carries a high rate of false-positivity and should be confirmed using a second and more specific diagnostic technique. In the absence of further testing, platelet and white blood cell counts are helpful for the correct interpretation.

We studied 2,259 German citizens after they returned from dengue-endemic countries from 1996 to 2004. Serotype-specific dengue antibodies indicated acute infections in 51 (4.7%) travelers with recent fever and 13 (1.1%) travelers with no recent fever, depending largely on destination and epidemic activity in the countries visited.

The prevalence of dengue antibodies was determined in the Attapeu region of South Laos with 225 blood samples collected from mostly febrile patients during the rainy season August - October 2001. An IgM capture ELISA was positive for one (0.4%) sample, while 177 (79%) samples were positive in an indirect IgG ELISA. Of the positive IgG samples, 20 (11.3%) were also positive on blood slides for Plasmodium falciparum. Dengue fever seems to be widespread in this area, but clinical dengue diagnosis remains difficult, especially in the first days of illness when physicians have to discriminate between dengue and other febrile illnesses.

Travelers have the potential both to acquire and to spread dengue virus infection. The incidence of dengue fever (DF) among European travelers certainly is underestimated, because few centers use standardized diagnostic procedures for febrile patients. In addition, DF is currently not reported in most European public health systems. Surveillance has commenced within the framework of a European Network on Imported Infectious Disease Surveillance (TropNetEurop) to gain information on the quantity and severity of cases of dengue imported into Europe. Descriptions of 294 patients with DF were analyzed for epidemiological information and clinical features. By far the most infections were imported from Asia, which suggests a high risk of DF for travelers to that region. Dengue hemorrhagic fever occurred in 7 patients (2.4%) all of whom recovered. Data reported by member sites of the TropNetEurop can contribute to understanding the epidemiology and clinical characteristics of imported DF.

Dengue virus infection is becoming increasingly recognized as one of the world's major emerging infectious diseases. Although only a few systematic studies have been conducted to assess the incidence and clinical course of dengue fever in travelers, it is now possible to estimate risk factors for travelers to areas of endemicity. Dengue virus and its vector, Aedes mosquitoes, benefit from human habitation and travel-related aspects of human behavior. Thus, travelers serve an important double role as potential victims of the disease and as vehicles for further spread of dengue.

In order to determine the influence of rheumatoid factor in serum specimens on the specificity of an immunochromatographic test for the detection of antibodies against dengue virus, 50 clinical specimens containing rheumatoid factor were evaluated for cross reactivity with a commercially available assay. While specificity for the detection of immunoglobulin (Ig) G antibodies was 100%, the IgM component of the test showed false-positive results in 26% of cases. Thus, it is important to consider interference by rheumatoid factor when using immunochromatographic assays for the detection of specific IgM produced during dengue infection.

Background: Dengue has been recognized as a potential hazard to tourists. A prospective, controlled study in the outpatient clinic of a German infectious disease clinic was conducted to assess the prevalence of dengue virus infection among international travelers., Methods: Serum samples from 130 patients with signs or recent history clinically compatible with dengue (fever, headache, muscle and joint pain, or rash), 95 matched controls with diarrhea, and 26 patients who never visited a country endemic for dengue were investigated., Results: Nine (6.9%) of the 130 patients with compatible symptoms and 1 (1%) of the 95 controls with diarrhea developed rising antibody titers against dengue virus. Of these 10 patients with probable dengue infection, 6 had been to Thailand, 2 to Malaysia, and 1 each to Indonesia and Brazil., Conclusions: Infection with dengue virus appears to be a realistic threat to travelers to Southeast Asia. Symptoms commonly associated with dengue, such as fever, myalgia, arthralgia, and vomiting, can be helpful for diagnosis when present, but the absence of typical symptoms does not exclude infection.

Sera from 20 patients with acute dengue fever were tested on their cross reactivities to other flaviviruses, especially against tick-borne encephalitis (TBE). One of the test systems used, indirect immunofluorescence (IIFT), was shown to exhibit strong cross reactivity. The reactivity pattern of sera from patients with pre-existing vaccine-induced antibodies against TBE or yellow fever was found similar to dengue secondary antibody response. In plaque reduction neutralization tests (PRNT) no cross reactions between different flaviviruses were found. The results show that PRNT is the most specific test system for differentiation of flavivirus antibodies.