Dengue

Dengue Bulletin Volume 28 (2004)

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Annual Changes of Predominant Dengue Virus Serotypes in Six Regional Hospitals in Thailand
from 1999 to 2002

Surapee Anantapreecha*^#, Sumalee Chanama*, Atchareeya A-nuegoonpipat*, Sirirat Naemkhunthot*, Areerat Sa-ngasang*, Pathom Sawanpanyalert*
and Ichiro Kurane**

*National Institute of Health, Department of Medical Sciences, Ministry of Public Health,
88/7, Tivanond Road, Muang, Nonthaburi, 11000, Thailand
**Department of Virology I, National Institute of Infectious Diseases Toyama, Shinjuku-ku,
Tokyo 162-8640, Japan

Introduction

The dengue virus consists of four serotypes: DEN-1, DEN-2, DEN-3 and DEN-4. The clinical manifestations range from undifferentiated febrile illness to classic dengue fever (DF), dengue haemorrhagic fever (DHF) and to dengue shock syndrome (DSS)^[1-3]. Dengue virus infections are now important public health problems in many tropical and subtropical areas in the world. In Thailand, a dengue outbreak first occurred in Bangkok in 1958. It then
occurred in a pattern of 2-year cycle, and subsequently in irregular cycles as the disease spread throughout the country. The largest outbreak was reported in 1987, with 174,284 reported cases, an incidence rate of 325 cases per 100,000 population. It was followed by another outbreak in 2001, which reported an incidence rate of 224 cases per 100,000 population^[2,4,5]. In 2002, 114,800 dengue cases were reported with an incidence rate of 183 cases per 100,000 population. It is important to determine which of the four serotypes causes the
dengue epidemic each year, and whether the dominant serotype is the same or different in each region in the country. In the present study, we analysed the predominant dengue serotypes at the six regional hospitals located in the four regions of Thailand – north,

north-east, central and south regions – in each year from 1999 to 2002.

Materials and methods

Collection of blood specimens

A total of 5,160 and 3,619 blood specimens were collected at acute and convalescent stages, respectively, from suspected dengue cases who visited Lampang Hospital in Lampang (north), Maharat Nakhon Ratchasima Hospital in Nakhon Ratchasima (north-east), Pathum Thani Hospital in Pathum Thani, Chareonkrung Pracharak Hospital in Bangkok, Ratchaburi Hospital in Ratchaburi (central) and Hadyai Hospital in Songkhla (south) from 1999 to 2002 (Figure 1). Blood specimens were drawn into tubes with ethylene diamine tetaacetate (EDTA) anticoagulant and centrifuged. The number of specimens ranged from 1 to 3 per patient. The first samples were collected on the day of hospitalization and the second samples were collected on the day of discharge. Third samples, if any, were collected between 10-14 days after the onset of symptoms. Plasma and buffy coat were separated at each hospital, kept in liquid nitrogen and then transported to the Arbovirus Section of the National Institute of Health, Nonthaburi. Specimens were kept at -70 °C for virus isolation.

Figure 1. Location of six provinces where the sentinel sites were chosen

1 = Lampang 2 = Nakhon Ratchasima 3 = Pathum Thani 4 = Bangkok 5 = Ratchaburi and 6 = Songkhla

Virus isolation and determination of dengue virus serotypes

Ten microlitres of acute phase-buffy coat samples were inoculated onto monolayer of C6/36 cells in a 24-well plate with rocking for 90 minutes at room temperature^[6]. The inocula were discarded and replaced by Leibovitz 15 medium (L-15, Gibco BRL) containing 1% heat-inactivated fetal bovine serum. After 7 days of incubation at 28 °C, the cultured media were collected, the infected cells were stained by IFA, and dengue virus serotypes were determined^[7,8]. DEN-1 (16007 strain), DEN-2 (16681 strain), DEN-3 (16562 strain) and DEN-4 (1032 strain) were used as virus controls in IFA.

Results and discussion

The numbers of samples tested and found positive for virus isolation are shown in Table 1.

Table 1. Number of samples used for the analysis

All the four dengue serotypes were detected in the six hospitals during this study. When the total numbers of isolates were analysed, DEN-1 was the predominant serotype (48%), followed by DEN-2 (27%), DEN-3 (20%) and DEN-4 (5%).

The predominant dengue virus serotypes in each hospital were analysed when more than nine isolates were obtained in a year. In the LampangHospital, the predominant serotypes were DEN-2 (44%) in 1999, DEN-1 (86%) in 2000, DEN-1 (57%) in 2001 and DEN-2 (79%) in 2002. In the MaharatNakhonRatchasimaHospital, the predominant serotypes were DEN-1 (47%) in 2001 and DEN-1 (57%) in 2002. In the PathumThaniHospital, the predominant serotypes were DEN-1 and DEN-2 (41% each) in 2001 and DEN-1 (47%) in 2002. In the ChareonkrungPracharakHospital, the predominant serotypes were DEN-1 (50%) in 2000, DEN-1 (61%) in 2001 and DEN-1 (65%) in 2002. In the RatchaburiHospital, the predominant serotypes were DEN-1 and DEN-2 (32% each) in 1999, DEN-3 (52%) in 2000, DEN-1 (38%) and in 2001 and DEN-2 (74%) in 2002. In the HadyaiHospital, the predominant serotype was DEN-1 (95%, 79% and 44%) in 2000, 2001 and 2002, respectively.

The predominant serotypes were compared among six hospitals in each of the study years (Table 2). In 1999 when data were analysed for two hospitals (Lampang and Ratchaburi), DEN-2 was predominant in one hospital (Lampang), and DEN-1 and DEN-2 were equally predominant in the other hospital (Ratchaburi). In 2000 when data were analysed for four hospitals (Lampang, Chareonkrung Pracharak, Ratchaburi and Hadyai), DEN-1 and DEN-3 were predominant in three hospitals (Lampang, Chareonkrung Pracharak and Hadyai) and one hospital (Ratchaburi), respectively. In 2001, DEN-1 was predominant in five hospitals (Lampang, Maharat Nakhon Ratchasima, Chareonkrung Pracharak, Ratchaburi and Hadyai) and DEN-1 and DEN-2 were equally predominant in one hospital (Pathum Thani). In 2002, DEN-1 and DEN-2 were predominant in four hospitals (Maharat Nakhon Ratchasima, Pathum Thani, Chareonkrung Pracharak and Hadyai) and two hospitals (Lampang and Ratchaburi), respectively. These results suggest that DEN-1 was the most predominant serotype from 1999 to 2002 in Thailand; however, the predominant serotypes were different in different hospitals.

The results of the present study are generally consistent with those previously reported. The analysis of dengue virus isolates at Bangkok Children’s Hospital from 1973 to 1999 showed changes in dengue virus serotypes from year to year^[9]. Although our study leads to a similar conclusion, the study was conducted in six regional hospitals throughout the country and not only in central Bangkok.

Each dengue serotype may possess unique characteristics in a dengue epidemic and disease severity. There were associations between DEN-1, DEN-2 and DEN-3 and moderately severe dengue epidemic years (1984-85, 1989-90, 1997), and between DEN-3 and severe dengue epidemic years (1987 and 1998)^[9]. In that sense, it is important to collect more information on the predominant serotypes and levels of epidemics. Although the present study generated information on isolates only from the patients who visited the six hospitals, they are located far away from each other in four regions of Thailand: north, north-east, central and south. It is thus assumed that the results of this study demonstrate, to a certain extent, the general features of dengue epidemics in Thailand.

Table 2. Proportion of each of the four dengue serotypes determined by virus isolation in the six hospitals

Acknowledgements

We thank Dr Piyaporn Bowonkiratikachorn and Ms Souvapa Pongsathaporn of Charoenkrung Pracharak Hospital, Dr Wandhana Sritubtim and Mr Suthichai Pongmonjit of Pathum Thani Hospital, Dr Vitaya Jiwariyaves and Ms Vanna Pengruangrojanachai of Ratchaburi Hospital, Dr Paiboon Vechpanich and Mr Prayuth Kaewmalang of Maharat Nakhon Ratchasima Hospital, Dr Wilaiwan Gulgonkarn, Dr Aroonrat Suwanarat and Mr Somchai Niyomthai of Lampang Hospital and Dr Suda Chubuppakarn and Ms Raruay Jitsakulchaidej of Hadyai Hospital, and other doctors, nurses and laboratory staff for assisting us with the collection of samples.

This work was partly supported by grants from the Department of Medical Sciences, Ministry of Public Health, Thailand, and the Japan Health Science Foundation.

References

1.      George R and Lum LCS. Clinical spectrum of dengue infection. In Gubler D and Kuno G (Eds.) Dengue and dengue hemorrhagic fever. Colorado: US Department of Health and Human Services, 1997: 89-113.

2.      World Health Organization. Monograph on dengue/dengue haemorrhagic fever. WHO, Regional Office for South-East Asia, New Delhi 1993.

3.      World Health Organization. Dengue haemorrhagic fever. Diagnosis treatment, prevention and control, 2nd edition. Geneva: WHO, 1997.

4.      Office of the Permanent Secretary for Public Health. Annual Epidemiological Surveillance Report 1993. Ministry of Public Health, Thailand.

5.      Office of the Permanent Secretary for Public Health. Annual Epidemiological Surveillance Report 2001. Ministry of Public Health, Thailand.

6.      Igarashi A. Isolation of Singh’s Aedes albopictus cell clone sensitive to dengue and chikungunya viruses. J Gen Virol, 1978, 40: 531-544.

7.      Henchal EA, Gentry MK, McCrown JM and Brandt WE. Dengue virus – specific and flavivirus group determinants identified with monoclonal antibodies by indirect immunofluorescence. Am J Trop Med Hyg, 1982, 31: 830-836.

8.      Henchal EA, McCown JM, Seguin MC, Gentry MK and Brandt WE. Rapid identification of dengue virus isolates by using monoclonal antibodies in an indirect immunofluorescence assay. Am J Trop Med Hyg, 1983, 32: 164-169.

9.      Nisalak A, Endy TP, Nimmannitya S, Kalayanarooj S, Thisayakorn U, Scott RM, Burke DS, Hoke CH, Innis BL and Vaughn DW. Serotype-specific dengue virus circulation and dengue disease in Bangkok, Thailand from 1973 to 1999. Am J Trop Med Hyg, 2003, 68(2): 191-202.