Annual Changes of Predominant Dengue Virus Serotypes in Six Regional Hospitals in Thailand from 1999 to 2002
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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 Abstract A virological study was conducted in six hospitals spread across Thailand from 1999 to 2002. All four dengue serotypes were identified, of which DEN-1 was the most predominant. The predominant dengue serotypes changed every 1-2 years in three of the six hospitals and the predominant serotypes were different in different hospitals. DEN-1 was predominant in two hospitals during three years of the study period (2000-2002). DEN-4 was not isolated, or accounted for only a small percentage of the total isolates, except in one hospital in 2002. Keywords: Dengue virus, dengue virus serotypes, Thailand. Introduction occurred in a pattern of 2-year cycle, and subsequently in irregular cycles as the The dengue virus consists of four serotypes: disease spread throughout the country. The DEN-1, DEN -2, DEN-3 and DEN-4. The largest outbreak was reported in 1987, with clinical manifestations range from 174,284 reported cases, an incidence rate undifferentiated febrile illness to classic of 325 cases per 100,000 population. It was dengue fever (DF), dengue haemorrhagic followed by another outbreak in 2001, fever (DHF) and to dengue shock syndrome which reported an incidence rate of 224 [1-3] (DSS) . Dengue virus infections are now cases per 100,000 population[2,4,5]. In 2002, important public health problems in many 114,800 dengue cases were reported with tropical and subtropical areas in the world. an incidence rate of 183 cases per 100,000 In Thailand, a dengue outbreak first population. It is important to determine occurred in Bangkok in 1958. It then which of the four serotypes causes the # E-mail: [email protected]; Tel.: 66 29510000 Ext. 99219, 99220; Fax: 66 25915449 Dengue Bulletin – Vol 28, 2004 1 Dengue Virus Serotypes in Thailand dengue epidemic each year, and whether Figure 1. Location of six provinces where the dominant serotype is the same or the sentinel sites were chosen 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 1 = Lampang (north-east), Pathum Thani Hospital in 2 = Nakhon Ratchasima 3 = Pathum Thani Pathum Thani, Chareonkrung Pracharak 4 = Bangkok Hospital in Bangkok, Ratchaburi Hospital in 5 = Ratchaburi and Ratchaburi (central) and Hadyai Hospital in 6 = Songkhla 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 Virus isolation and determination of hospitalization and the second samples of dengue virus serotypes were collected on the day of discharge. Ten microlitres of acute phase-buffy coat Third samples, if any, were collected samples were inoculated onto monolayer between 10-14 days after the onset of of C6/36 cells in a 24-well plate with symptoms. Plasma and buffy coat were rocking for 90 minutes at room separated at each hospital, kept in liquid temperature[6]. The inocula were discarded nitrogen and then transported to the and replaced by Leibovitz 15 medium (L- Arbovirus Section of the National Institute of 15, Gibco BRL) containing 1% heat- Health, Nonthaburi. Specimens were kept inactivated fetal bovine serum. After 7 days at -70 °C for virus isolation. of incubation at 28 °C, the cultured media were collected, the infected cells were 2 Dengue Bulletin – Vol 28, 2004 Dengue Virus Serotypes in Thailand stained by IFA, and dengue virus serotypes Results and discussion were determined[7,8]. DEN -1 (16007 strain), DEN -2 (16681 strain), DEN-3 (16562 The numbers of samples tested and found strain) and DEN-4 (1032 strain) were used positive for virus isolation are shown in as virus controls in IFA. Table 1. Table 1. Number of samples used for the analysis Convalescent Virus isolation Year Hospital Acute sample sample positive 1999 Lampang 128 108 74 Maharat Nakhon Ratchasima 26 18 6 Pathum Thani 0 0 0 Chareonkrug Pracharak 0 0 0 Ratchaburi 35 11 31 Hadyai 1 1 0 2000 Lampang 35 33 15 Maharat Nakhon Ratchasima 22 17 3 Pathum Thani 25 14 4 Chareonkrug Pracharak 15 15 10 Ratchaburi 438 419 238 Hadyai 113 28 22 2001 Lampang 262 238 150 Maharat Nakhon Ratchasima 358 251 176 Pathum Thani 265 170 143 Chareonkrug Pracharak 224 216 99 Ratchaburi 389 363 256 Hadyai 450 231 276 2002 Lampang 339 236 95 Maharat Nakhon Ratchasima 930 600 292 Pathum Thani 154 73 32 Chareonkrung Pracharak 135 128 65 Ratchaburi 490 346 170 Hadyai 326 103 77 All the four dengue serotypes were The predominant dengue virus detected in the six hospitals during this serotypes in each hospital were analysed study. When the total numbers of isolates when more than nine isolates were obtained were analysed, DEN-1 was the predominant in a year. In the Lampang Hospital, the serotype (48%), followed by DEN -2 (27%), predominant serotypes were DEN-2 (44%) DEN-3 (20%) and DEN -4 (5%). in 1999, DEN-1 (86%) in 2000, DEN-1 Dengue Bulletin – Vol 28, 2004 3 Dengue Virus Serotypes in Thailand (57%) in 2001 and DEN-2 (79%) in 2002. In predominant in four hospitals (Maharat the Maharat Nakhon Ratchasima Hospital, Nakhon Ratchasima, Pathum Thani, the predominant serotypes were DEN-1 Chareonkrung Pracharak and Hadyai) and (47%) in 2001 and DEN-1 (57%) in 2002. In two hospitals (Lampang and Ratchaburi), the Pathum Thani Hospital, the respectively. These results suggest that DEN - predominant serotypes were DEN-1 and 1 was the most predominant serotype from DEN-2 (41% each) in 2001 and DEN-1 1999 to 2002 in Thailand; however, the (47%) in 2002. In the Chareonkrung predominant serotypes were different in Pracharak Hospital, the predominant different hospitals. serotypes were DEN-1 (50%) in 2000, DEN - 1 (61%) in 2001 and DEN -1 (65%) in 2002. The results of the present study are In the Ratchaburi Hospital, the predominant generally consistent with those previously serotypes were DEN-1 and DEN-2 (32% reported. The analysis of dengue virus each) in 1999, DEN-3 (52%) in 2000, DEN- isolates at Bangkok Children’s Hospital from 1 (38%) and in 2001 and DEN -2 (74%) in 1973 to 1999 showed changes in dengue [9] 2002. In the Hadyai Hospital, the virus serotypes from year to year . Although predominant serotype was DEN-1 (95%, our study leads to a similar conclusion, the 79% and 44%) in 2000, 2001 and 2002, study was conducted in six regional respectively. hospitals throughout the country and not only in central Bangkok. The predominant serotypes were compared among six hospitals in each of the Each dengue serotype may possess study years (Table 2). In 1999 when data unique characteristics in a dengue epidemic were analysed for two hospitals (Lampang and disease severity. There were and Ratchaburi), DEN-2 was predominant associations between DEN-1, DEN-2 and in one hospital (Lampang), and DEN-1 and DEN-3 and moderately severe dengue DEN-2 were equally predominant in the epidemic years (1984-85, 1989-90, 1997), other hospital (Ratchaburi). In 2000 when and between DEN-3 and severe dengue [9] data were analysed for four hospitals epidemic years (1987 and 1998) . In that (Lampang, Chareonkrung Pracharak, sense, it is important to collect more Ratchaburi and Hadyai), DEN-1 and DEN-3 information on the predominant serotypes were predominant in three hospitals and levels of epidemics. Although the (Lampang, Chareonkrung Pracharak and present study generated information on Hadyai) and one hospital (Ratchaburi), isolates only from the patients who visited respectively. In 2001, DEN-1 was the six hospitals, they are located far away predominant in five hospitals (Lampang, from each other in four regions of Maharat Nakhon Ratchasima, Chareonkrung Thailand: north, north-east, central and Pracharak, Ratchaburi and Hadyai) and south. It is thus assumed that the results of DEN-1 and DEN-2 were equally this study demonstrate, to a certain extent, predominant in one hospital (Pathum Thani). the general features of dengue epidemics In 2002, DEN-1 and DEN -2 were in Thailand. 4 Dengue Bulletin – Vol 28, 2004 Dengue Virus Serotypes in Thailand Table 2. Proportion of each of the four dengue serotypes determined by virus isolation in the six hospitals Year Hospital Total DEN-1 (%) DEN-2 (%) DEN-3 (%) DEN-4 (%) 1999 Lampang 74 31 (42) 33 (44) 8 (11) 2 (3) Maharat Nakhon 6 4 (67) 2 (33) 0 (0) 0 (0) Ratchasima Pathum Thani 0 0 (0) 0 (0) 0 (0) 0 (0) Chareonkrug 0 0 (0) 0 (0) 0 (0) 0 (0) Pracharak Ratchaburi 31 10 (32) 10 (32) 8 (26) 3 (10) Hadyai 0 0 (0) 0 (0) 0 (0) 0 (0) 2000 Lampang 15 13 (86) 1 (7) 0 (0) 1 (7) Maharat Nakhon 3 2 (67) 1 (33) 0 (0) 0 (0) Ratchasima Pathum