Status of Dengue Control Programme in Taiwan − 2001 by
Huan-Yao Lei*#, Jyh-Hsiung Huang**, Kao-Jean Huang* and Chungming Chang*** *Departments of Microbiology & Immunology, College of Medicine, National Cheng Kung University, Tainan, Taiwan, Republic of China **Center for Disease Control, Department of Health, The Executive Yuan, Taiwan, Republic of China ***Department of Intramural Research Affair, National Research Health Institute, Taiwan, Republic of China Abstract Taiwan is a dengue-epidemic area and epidemiological studies have shown that most indigenous dengue cases can be traced to imported cases preceding the local transmission. Thus, the critical issue in dengue prevention and control is to identify the index case of imported dengue patient, then break the dengue virus transmission as quickly as possible. The Dengue Prevention and Control Centre, which is responsible for dengue control in Taiwan, is a joint programme organized by the Department of Health and the Environmental Protection Administration, with the participation of both the Central and local governments, started at 1988. There are seven working groups in the centre which deal with various affairs including epidemiology, entomology, insecticide application, virology, medical care, source reduction and health education for total coordination. To further strengthen this programme, international collaboration in surveillance, epidemic information exchange, as well as understanding the pathogenesis of dengue haemorrhagic fever and dengue shock syndrome and prevention of the disease process is necessary. Keywords: Dengue virus, mosquito surveillance, mosquito control, law enforcement, indigenous dengue case, health education, Taiwan.
Dengue in Taiwan Aedes aegypti and Aedes albopictus are the two main vectors involved in the transmission of dengue in Taiwan. The former is active in indoor settings, primarily distributed between the south of Putai and the north of Hengchun below 1 000 m, and # For correspondence: hyleimail.ncku.edu.tw
the latter is found outdoors and is widely distributed in the plains and mountainous regions up to an altitude of 1,500 m throughout Taiwan. As a day-biting mosquito that prefers to feed on humans, Aedes aegypti is responsible for most epidemics. Several outbreaks of dengue fever were
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Status of Dengue Control Programme in Taiwan - 2001
recorded in Taiwan even before World War II. No dengue case was reported since 1945 until 1981 when a DEN-2 outbreak occurred in Liouchiou Township of Pingtung County. In 1987, a DEN-1 outbreak occurred in the southern part of Taiwan. The major outbreaks of dengue fever in Taiwan are included in Table 1. Dengue haemorrhagic fever cases were taken into account since 1994. An analysis of the monthly frequency of indigenous dengue cases shows that it peaks around September-December, which is quite different from that in south-east Asia(1). Local strains of all four dengue serotypes were isolated from various regions of Taiwan as shown in Figure 1. Using the year 2000 as an example, various serotypes of dengue virus were isolated from imported and/or indigenous cases (Table 2). While one DEN-3 virus was isolated from imported cases, one DEN-3 and 10 DEN-4 viruses were isolated from indigenous cases. Although the isolation rate is low, probably due to the timing of sample collection, it is difficult to isolate dengue virus from blood samples collected beyond seven days postfever onset. The dengue virus isolation provides important information for our dengue control programme. The characteristic of dengue virus infection in Taiwan is that most indigenous dengue cases can be traced back to imported cases preceding the local infection, although the issue of “Whether dengue is endemic in Taiwan” is debated. The control strategy is based on the assumption that dengue transmission is from an imported case as its success indicates that dengue virus is primarily imported into Taiwan island every year.
Table 1: Major outbreaks of dengue fever in Taiwan, 1981-2001 Year Index case Epidemic Infection Serotype area rate >80% 13% DEN-2 DEN-1, 2, 4 DEN-1, 3, 4 DEN-1, 2, 4 DEN-1, 3 DEN-1, 3 DEN1,2,3
1981 Liouchiou Liouchiou 1987 Pingtung, South Kaohsiung 1988 Pingtung, South Kaohsiung 1989 Pingtung, South Kaohsiung 1991 Kaohsiung Kaohsiung
–
–
–
1994 Kaohsiung South county 1995 Taipei county, North, Middle, South Taipei, Kaohsiung Tainan city Kaohsiung city Tainan city
–
–
1996 Taipei
–
DEN-1, 3 DEN-2
1997 Tainan city 1998 Kaohsiung city Tainan city
–
–
DEN-2 DEN-3
1999 Kaohsiung Kaohsiung 2000 Tainan city Tainan city
– –
DEN-1 DEN-4
2001 Kaohsiung Kaohsiung city city −=Information not available
–
DEN-2
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Table 2. Virus isolation by countries and from imported and indigenous dengue case during 2000 Region of infection Philippines Indonesia Malaysia Imported Cases Cambodia Laos Malaysia or Thailand Viet Nam Bangladesh India Costa Rica Bangladesh or Indonesia Imported cases 1 9 3 2 1 1 1 2 1 1 1 Indigenous cases 2 95 2 3 125 Serotypes+ DEN-3 1 DEN-4 Serotypes DEN-3 1 2 DEN-4 10 10
Residental area Indigenous Cases * ** + _
Pingtung County Tainan City Kaohsiung County * Taipei County **
Grand total One of the cases was infected in Tainan City Two of the cases were infected in Tainan City Typed by RT-PCR or virus isolation No virus isolation
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Figure 1: Serotype of dengue virus isolated from various regions of Taiwan
DEN-1-2
DEN-1
Dengue control programme A joint dengue prevention and control centre was set up in December 1988 by the Department of Health and the Environmental Protection Administration to plan programmes for the prevention and control of dengue after an outbreak in southern Taiwan. In April 1990, the Executive Yuan approved a five-year plan for the control of dengue fever for implementation. Seven working groups were organized to conduct disease surveillance, laboratory diagnosis, vectors surveillance, insecticide application, source reduction, medical care, and health education to Dengue Bulletin – Vol 26, 2002
supervise local governments to carry out control measures. This programme has been extended for another five years and has now become permanent since 2001. These components and their responsibilities are discussed below:
Surveillance system To strengthen disease surveillance for dengue fever, the administration set up an active surveillance system throughout the country. In addition to the routine reporting system by physicians, several routes are established to find potential cases: (i) the
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public are encouraged to come forward for testing; (ii) health statements of inbound passengers are reviewed; (iii) specimens of patients with unknown fevers are collected for laboratory diagnosis; (iv) schools are asked to report any probable cases; (v) blood specimens are collected from communities; (vi) specimens from other fevers are serologically screened; and (vii) contacts of confirmed cases are investigated for early detection of cases to prevent the spread of the infection.
virus introduction. If the patient had travelled abroad in the past two weeks, it will be recognized as an imported case. When travelling abroad has been excluded, it will be recorded as an indigenous case. For an indigenous case, the neighbouring 50 households would be interviewed to determine the possible source of infection. More than 100 blood specimens are mandatory to be collected with free and informed consent by local public health personnel to determine the degree of the virus spread. The unique characteristic of dengue transmission in Taiwan is that the importation of the DEN virus occurs through travellers from south-east Asia. Thus, it is very critical to identify the index case of imported dengue patient as quickly as possible, and then break the dengue virus transmission by mosquito vector with insecticides. The success of this approach has been demonstrated from the incidence of dengue cases that occurred in 1987-2001. A large dengue outbreak of 4,389 cases occurred in 1988. After the implementation of the dengue control programme, dengue incidence has been reduced to less then 400 cases per year (Figure 2). However, during the 1998 dengue pandemic, Taiwan Island was also affected. Sporadic cases of both imported and indigenous cases were found. All four dengue serotypes were identified from indigenous cases in Kaohsiung city during August. Among these, a small outbreak with a total of 50 confirmed cases was detected in SenMin district in September. The virus was isolated as DEN-2. The peak of Kaohsiung outbreak was around early November. Tainan city in the north was the next target. The first index case in Tainan city was reported and confirmed on Dengue Bulletin – Vol 26, 2002
Laboratory diagnosis Every dengue case is confirmed by laboratory diagnosis. All serum specimens collected from suspected cases were tested by capture IgM and IgG ELISA. Serum specimens collected within 7 days of the onset were also tested by RT-PCR and virus isolation. A confirmed dengue case is defined as follows: (i) positive for dengue virus isolation; or (ii) positive for dengue virus genomic sequence by RT-PCR; or (iii) four-fold increase of dengue virus-specific IgM or IgG antibody in paired serum samples where cross-reactions to JE have been excluded; or (iv) positive for dengue virus-specific IgM and IgG in a single serum sample where cross-reactions to JE have been excluded. All these assay kits are developed by the Center of Disease Control, Taiwan. Laboratory results are to be completed within 24 hours for ELISA, 48 hours for RT-PCR and 14 days for virus isolation. The results are faxed to local public health bureaus as soon as possible for further action. Local public health personnel then conduct an epidemiological survey and investigate the potential source of dengue
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November 1 (Figure 3). This was identified as an indigenous case because the patient had not travelled abroad in the past two weeks. Active surveillance in the neighbourhood identified two more cases. After epidemiological interview, these two cases were traced back to have had dengue symptoms on October 24 and 30. They both had not travelled abroad, and therefore were both indigenous cases. The virus was isolated as DEN-3, which was distinct from the one that occurred in Kaohsiung city. This suggested that the DEN-3 virus had been circulating in Tainan city for a while. The surveillance system failed to detect it early enough, due probably to the political transition period for the new city mayor and operational failures of local public health
bureaus of the Tainan city government. Dengue virus with Aedes aegypti had spread from the sub-district area to the whole city during November and December. The local environmental protection administration undertook vector control activities and brought it under control by late December. The surveillance system has since been improved after this bitter experience in the 1998 outbreak. This example explains the uniqueness of dengue transmission in Taiwan where the major source of dengue virus comes from south-east Asia. The most critical element for dengue control is to identify the index case of imported dengue patient, then break the dengue virus transmission cycle as quickly as possible.
Figure 2. Figure 2. Confirmed Dengue Cases in Taiwan from 1987 to 2001
4000 600 550
4,389 527
Total cases Indigenous case Imported cases
Confirmed Dengue Patients
500 450 400 350 300 250 200 150 100 50 0 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 35 16 10 0 175 149 56 20 76 19 69 40 140 113 244 222 369 329 280 238 224 348
23 4
13 0
Years
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Figure 3: Dynamics of dengue outbreak in Tainan city from late 1998 to early 1999 7
Total 137 cases (1998.10.24~1999.1.11) 11 20 1123 1127
6
11 25
12 06
1207
0926 1116
11 22
12 02 1203 1205
1128
1022
5
1216
C ase num ber
4 11 17 0928 11 18 11 19 1124
1220 1209 12 11 1217 12 19
1204
12 23
1222
1101 1103 1228
1 024(1998 )
1017 1212 1019
0923 1113
0911
3
11 08
1121
1126
1201
1
0 0 7 14 21 28 35 42 49 56 63 70 77 84
Onset day
(Updated and reproduced with the kind permission of the Australasian Medical Publishing Company (6))
Entomological surveillance In vector surveillance, local public health bureaus routinely conduct mosquito surveys and control measures are enforced if the mosquito density reaches alarming levels. Breteau Index is routinely used for the measurement of mosquito larval density and level three is set to start control measure. The main vectors of dengue in Taiwan are Aedes aegypti and Aedes albopictus. The distribution of the former species is geographically limited to areas south of Taiwan, and this species is more important in the epidemiology of dengue in southern Taiwan. Aedes albopictus is distributed throughout the island, below an elevation of 1,500 m above sea level. This mosquito is
responsible for epidemics of dengue in those areas where Aedes aegypti is non-existent, such as the small outbreaks in Chungho, Taipei County; Tung-Hai University, Taichung; and Taipei city. The main breeding containers of dengue vectors in Taiwan are flower vases, water buckets, tyres, bottles, refrigerator receptacles, earthenware jars and concrete tanks. Figure 4 shows the distribution of Aedes as measured by Breteau Index by Administrative Area in May 2001. This type of information is released every month to alert the public about the risk of developing dengue fever. An annual training programme, which includes both basic knowledge and field practice, is also conducted for dengue control personnel.
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1230 0101(1 999) 010 2(1999)
1129 1130
1225 1226 12 27
12 08
1221
0111(1 999 )
2
1101* 1103
1030
1109 1111 11 12
1213
1214
12 24
1109
Status of Dengue Control Programme in Taiwan - 2001
Figure 4: The distribution of Aedes measured by Breteau Index by administrative area in May 2001
Insecticide application and source reduction Environmental Protection Administration units carry out survey of surrounding areas of confirmed indigenous cases, i.e. houses and work places within 50 metres. All these places will be sprayed with insecticides to reduce the vector source. Fogging was conducted using ULV fogging, both inside and outside the houses. The insecticides used were permissible pyrethroid formulations. The main insecticide contained pyrethrin as the major component including premethrin, alphacypermethrin, cyfluthrin and phenothrin.
Case management of DHF/DSS A mission-oriented group “DHF Clinical Consultants Group” led by experienced clinicians has been set up to help evaluate the suspected DHF cases and provide adequate medical care. Clinical diagnosis of DF and DHF/DSS was defined according to the criteria of the World Health Organization(3). However, physicians in Taiwan are generally not familiar with or alert to the symptoms of dengue haemorrhagic fever. There is a need to develop this expertise through an exchange programme of clinicians with centres of excellence in countries of south-east Asia.
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Health education The administration provides various media advertisements concerning dengue, especially the transmission and clinical symptoms. Reducing the mosquito vector source is demonstrated to be the most effective option to prevent the transmission of dengue fever. Awareness of dengue transmission helps people to protect themselves from infection.
jeopardize a restriction, ban, limitation or disposal by a local governing agency may constitute not only an immediate mandatory prosecution but also a fine ranging from NT 60,000 to NT 300,000 according to Article 41. Figure 5: Poster to award the report of suspected dengue infection
Law enforcement The Control of Communicable Diseases (CDC) Act was re-amended on 23 June 1999. Dengue fever is classified as category 3, sub-category A infectious disease, which should be reported within 24 hours. It is clearly specified that, in disease control, the role of the Central government is to provide technical assistance, and that the local government should strictly implement disease control measures according to regulations. CDC urges physicians who observe symptoms of dengue fever or other infectious diseases which pose danger of epidemics, to immediately report them to local public health bureaus and CDC, and cooperate in taking necessary measures to prevent the spread of the disease to the victims' immediate family members and others. Anyone who voluntarily reports to be infected and is later confirmed gets an award of NT 2,500. Figure 5 is a poster to encourage people to voluntarily report his/her dengue infection. On the contrary, according to the “Law on the Control of Communicable Diseases, Article 41” if any individual has been found to jeopardize any of the prohibitions or orders issued by a governing agency is punishable by a fine ranging from NT 10,000 to NT 150,000. Where any individual has been found to 22
Conclusion Dengue prevention and control centres including epidemiology, entomology, insecticide application, virology, medical care, source reduction and health education, have been organized both in the Central and local governments in Taiwan since 1988. This has successfully helped to reduce the incidence of dengue fever cases significantly. Zero indigenous case is the future goal of the dengue control programme. From previous studies and experience we know the major source of dengue virus comes from southeast Asia due to intensive travel between Taiwan and countries in south-east Asia. The critical issue is to identify the index case of Dengue Bulletin – Vol 26, 2002
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imported dengue patient and then break the dengue virus transmission as quickly as possible. This approach has been very effective since 1988. However, the cost is very high and the task is time-consuming. The future goal to resolve dengue virus infection is to understand the pathogenesis
of dengue haemorrhage fever and dengue shock syndrome(4) and interrupt the development of the disease process. Alternatively, developing the dengue vaccine is the final answer to prevent dengue virus infection.
References 1. Center of Disease Control (2001). Website of Center of Disease Control, Department of Health, The Executive Yuan, Taiwan <http:www.cdc.gov.tw>. King CC, Wu YC, Chao DY, Lin TH, Chow L, Wang HT, Ku CC, Kao CL, Chien LJ, Chang HJ, Huang JH, Twy SJ, Huang KP, Lam SK and Gubler DJ. Major epidemics of dengue in Taiwan in 19812000: Related to intensive virus activities in Asia. Dengue Bulletin, 2000, 24: 1-10. 3. Anonymous. Dengue Haemorrhagic Fever: Diagnosis, Treatment, Prevention and Control. World Health Organization, Geneva, 1997. Lei HY, Yeh, TM, Liu HS, Lin YS, Chen SH and Liu CC. Immunopathogenesis of dengue virus infection. J Biomed Sci, 2001, 8: 377-388.
4.
2.
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