Imported malaria and dengue fever in returned travelers in Japan from 2005 to 2010
Introduction
Fever is a common and important symptom of serious illness in returned travelers and frequently leads to hospitalization. A recent study of ill returned travelers that used the GeoSentinel Surveillance Network, a large multicenter database, defined the cause of fever according to place of exposure and traveler characteristics.1 Malaria and dengue are important febrile illnesses that are leading causes of fever in returning travelers, and respectively they account for 21% and 6% of the causes of fever according to the report from this network.2
Although this database is very useful due to its reduced population-specific bias, unlike many smaller studies from the West, the evaluation of travel-related febrile illness sometimes requires consideration of the characteristics of each country and its travelers, such as the most frequently visited destinations, the average duration of travel, and the immigrant population. In fact, Japanese travelers report considerably fewer cases of illness related to travel to tropical regions than travelers in European studies. This is likely to be attributable to the relatively fewer numbers who travel from Japan to countries in the African and South American regions.3
In Japan, indigenous malaria has been eradicated since 1959, and domestic transmission of dengue also has not been reported since 1946. Although the description of imported malaria and dengue cases has been limited to a small number of cases (less than 100 in recent years),4 due to the number of migrants visiting friends and relatives, the number of people volunteering alongside local residents, and the increasing numbers of Japanese adventure travelers, it is assumed that a larger number of travelers are at risk of contracting malaria and dengue. Recently, two reports were published describing imported malaria and dengue from different referral hospitals in Japan,5, 6 but most data were collected before 2000. The present study updates the current knowledge in this area by using more recent data from the National Centre for Global Health and Medicine, which represents the largest source of this data for Japan.
With the changes in diagnostic methods and drug choice in Japan and around the world in recent years, the aim of the present study is to describe the clinical characteristics of imported malaria and dengue cases in Japan, to gain understanding of the current clinical situation for malaria and dengue in Japan and also to provide useful information to update diagnosis and management for practitioners of travel medicine.
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Methods
The analysis was undertaken by accessing the records of patients who visited the National Centre for Global Health and Medicine in Tokyo, Japan, which is a governmental general hospital with about 900 inpatient beds, and which houses a travel clinic that is a GeoSentinel Network site. The clinic sees travelers for both pre-travel advice and for post-travel health problems. The patients of the present study included approximately 10% of the patients who visited the National Centre for Global
Malaria
There were 50 confirmed cases (34 men and 16 women, 40 were Japanese and 10 were non-nationals; mean and SD, 34.5 ± 12.6 years) and the 37 cases of them (74.0%) were hospitalized. Among the confirmed cases, 31 were Plasmodium falciparum, 12 were Plasmodium vivax, 6 were Plasmodium ovale, and 1 was Plasmodium malariae and P. falciparum mixed infection. Reasons for travel included business (n = 19, 38%); leisure (n = 10, 20%); visiting friends and relatives (n = 8, 16%); volunteering (n = 6, 12%);
Discussion
Regarding the area of travel, of the 50 malaria patients, 76.0% of them had contracted the disease in Africa, whereas among the 40 dengue patients, 90.0% of them had contracted the disease in Asia (Table 1). This result reflects the relative risk of post-travel illness related to different destination continents.1 However, because the number of Japanese travelers visiting South America is relatively low, only one case of dengue (2.5%) was confirmed in a patient returning from South America,
Funding
This work was supported in part by The Grant of National Centre for Global Health and Medicine (21A-107).
Conflict of interest
None declared.
Acknowledgements
The authors wish to thank Dr. Koichiro Kudo, Director of Disease Control and Prevention Centre, the National Centre for Global Health and Medicine, for helpful comments, Drs. Shuzo Kanagawa, Nozomi Takeshita and Mugen Ujiie for clinical support, Dr. M.L Moi for assistance with the detection of the dengue virus genome and titers, and Dr. Moritoshi Iwagami for assistance with microscopic observation and confirmation of malaria species.
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