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The topic of This Month Vol.36 No.3(No.421)

Dengue fever and dengue hemorrhagic fever, 2011-2014

(IASR 36: 33-35, March 2015)

Dengue virus is a member of the flavivirus family with four known serotypes, type 1-4.  It is transmitted to humans by mosquitoes Aedes aegypti and Aedes albopictus, via the human to mosquito to human cycle.  Ae. aegypti are often found in urban areas while Ae. albopictus is found in both urban and rural areas, including in much of Japan.  Persons bitten by infected mosquitoes develop clinical signs or symptoms, such as fever, exanthema and pain (mainly arthralgia), 3-7 days later (see pp.35, 38 & 41 of this issue, IASR 35: 241-242, 2014).  Dengue fever is endemic in many tropical/sub-tropical areas of the world (see p. 46 of this issue).  No commercialized vaccine or specific therapies are available (see p. 44 of this issue), and patients are treated symptomatically with rehydration and/or antipyretic analgesics.  Hemorrhage or shock syndrome, though rare, may occur; fatality can be reduced by appropriate treatments. 

1. National Epidemiological Surveillance of Infectious Diseases (NESID)
   Dengue fever is a Category IV infectious disease under the Infectious Diseases Control Law.  Physicians who have made a diagnosis of dengue fever must notify the cases immediately (see http://www.niid.go.jp/niid/images/iasr/36/421/de4211.pdf for notification criteria). 

During 2007-2009, 89-105 dengue cases were reported annually.  From 2010 to 2013, during each year, 244, 113, 221, and 249 cases were reported, respectively (Fig. 1 and Table 1).  In 2014, a total of 341 cases were notified, which included 179 imported cases and 162 autochthonous cases; it had been nearly 70 years since the last confirmed autochthonous dengue case was reported in Japan (see pp.35, 37& 38 of this issue).  In recent years, the majority of dengue virus serotypes detected among imported cases were type 1 (Table 2).  Among autochthonous cases detected in 2014, only serotype 1 was detected (see pp. 35, 37, 38 &40 of this issue). 

Seasonality: Historically, the number of reported dengue cases has been highest during August-September, including in 2011- 2014 (IASR 32: 159-160, 2011) (Fig. 1).  The trend is likely attributable to seasonality of travelers going abroad and the dengue activity level at their destinations (see p. 46 of this issue).  Among autochthonous cases in 2014, the majority (133 of 162 cases) were also diagnosed in September (Fig. 1).

Suspected place of infection: During 2011-2014, suspected place of infection included at least 37 countries/areas (Table 3).  During 2011-2013, 554 of 583 cases (95%) had visited Southeast and other Asian countries, such as Indonesia, the Philippines, Thailand, India, Cambodia, and Malaysia. There were also cases who had traveled to Central and South America, Oceania or Africa. Similarly, in 2014, 165 of 179 imported cases (92%) were suspected to have been infected in the Asian region. Among 162 autochthonous cases, 159 were suspected to be infected in Tokyo (see pp. 35 & 37 of this issue).

Gender and age: Among 762 imported cases reported in 2011-2014, 471 were male (62%) and 291 female (38%) . There were 218 cases in their 20s (29%), 201 cases in their 30s (26%) and 126 cases in their 40s (17%) (Fig. 2). Among 162 autochthonous cases in 2014, similarly, 95 (59%) were male. While the median age among autochthonous cases was 27 years, age distribution varied widely, from 4 to 77 years (Fig. 2). 

Dengue hemorrhagic fever: About 5% of all imported dengue cases in recent years were dengue hemorrhagic fever (DHF) cases [4/133 (4%) in 2011, 13/221 (6%) in 2012, 11/249 (4%) in 2013, and 8/179 (4%) in 2014)] (Table 1).  The median age among DHF cases was 32 years (range: 3-64 years).  There was no gender difference in the proportion of dengue cases that were DHF, with 23 DHF among 471 dengue cases (5%) in males and 13 DHF among 291 dengue cases (4%) in females. Among 162 autochthonous cases in 2014, there was only one DHF case (1%).  No fatal cases were reported during 2011-2014.  

2. Laboratory diagnosis
Prefectural and municipal public health institutes (PHIs) and the National Institute of Infectious Diseases (NIID) conduct laboratory diagnosis of dengue fever including virus isolation, viral genome detection by RT-PCR, and serological tests (e.g. IgM antibody detection and neutralization test) (see p. 40 of this issue).  Amendment of the Quarantine Law in November 2003 included dengue fever in the list of quarantine-authorized infectious diseases; enabling quarantine stations to offer medical examinations and laboratory testing to travelers coming from dengue fever endemic areas (IASR 35: 112-114, 2014).  The detection of the non-structural protein NS1 antigen was added to the notification criteria of dengue fever in April 2013, and during the domestic dengue fever epidemic in 2014, the rapid diagnostic kits based on NS1 antigen detection were distributed to the PHIs (see pp. 40 & 41 of this issue).  Since 2013, majority of laboratory diagnoses for dengue were RT-PCR  for viral genome detection, IgM antibody detection and NS1 antigen detection (Table 4).

3. Countermeasures in Japan
As Ae. albopictus, a dengue fever vector, inhabits Japan (see p. 42 of this issue), and as the number of imported cases coming from dengue endemic countries continue to increase, there is an ongoing concern for potential dengue outbreaks in Japan.  In 2014, dengue cases infected in Japan were also reported from abroad (see p. 39 of this issue). Prevention and countermeasures against dengue fever are important not only domestically but also internationally, given the ever increasing globalization of human travel.  For preventing the spread of mosquito-borne infectious diseases, such as dengue fever and chikungunya fever (see pp. 47 & 48 of this issue), the Ministry of Health, Labour and Welfare is planning to release the guidelines specific for mosquito-borne infectious diseases in April 2015.  The guidelines recommend, as necessary measures, (i) routine, ongoing implementation of control measures against mosquitoes that transmit infectious diseases, (ii) rapid detection of human cases of mosquito-borne infectious diseases, (iii) implementation of prompt and appropriate measures against mosquitoes in case of outbreaks, and (iv) provision of appropriate medical care to patients.  For combatting dengue fever, not only government and medical personnel but each and every citizen must actively participate.  

 

Copyright 1998 National Institute of Infectious Diseases, Japan