Virological Surveillance of Dengue Haemorrhagic Fever in Viet Nam,

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1 Virological Surveillance of Dengue Haemorrhagic Fever in Viet Nam, By Do Quang Ha *, # and Truong Uyen Ninh** * Pasteur Institute, Ho Chi Minh City ** National Institute of Hygiene and Epidemiology, Hanoi Abstract In Viet Nam during , the virological surveillance offered important information about circulating serotypes of dengue viruses. The activity cycle of 1 was from 1989 to The 2 activity cycle started in 1987 and remained active into first appeared in 1995 and continues to be active. 4 has strongly emerged since In southern Viet Nam, cases of dengue haemorrhagic fever are always confirmed in the first quarter of every year. Therefore, active surveillance and dengue control activities must be initiated during this period. Key words: Virologic surveillance, viral activity, dengue control, Vietnam. Introduction Since 1963, there has been a steady increase in the incidence of dengue haemorrhagic fever (DHF) in Viet Nam, which has been a major health problem and a leading cause of hospitalization and death of children. In northern Viet Nam, DHF was identified for the first time in 1959, where a major epidemic occurred in In the south, DHF first appeared in 1960, followed by an outbreak in 1963, resulting in 331 hospitalized children with severe haemorrhage, of whom 116 died. With the critical appearance of 2 in 1987 (!), the disease has been spreading with continuous increase in the number of cases and deaths. 1, 3 and 4 closely followed the circulation of 2. Data collected during on the viral investigation of these DHF epidemics are presented here. Materials and methods Virus isolation and identification Blood samples collected from acute DHF cases were stored at -20 C or -70 C until tested. The undiluted blood specimens (of 0.05 ml) were inoculated into duplicated 1 ml tubes of C6/36 (Aedes albopictus) tissue cells. The tubes were incubated at 28 o C for 7-10 days. Infected cell cultures were # For correspondence: phantu@hcmc.netnam.vn 18 Dengue Bulletin Vol 24, 2000

2 harvested and assayed for dengue virus by the direct and indirect fluorescent antibody technique, using the monoclonal antibody (MAB) SLE 6B6C-1/FITC conjugate and the serotype-specific MAB: 1 (Hawaii 15F and D2-1F1-3), 2 (NGC 3H5-1-21), 3 (H87 5D ), 4 (H241 1H10-6-7) and Japanese encephalitis (JE) (Nakayama 14H5) (1) All (2) hese MABs were supplied by the Centers for Disease Control and Prevention, Fort Collins, Colorado, USA. Results and discussion Virus isolation The details of DEN serotypes for the period are given in Table 1. From Table 1, it is evident that 1 was active during , 2 from 1987 to 1997, 3 came on the scene in 1995 and continues to be active, and 4 has emerged in Dengue viruses isolated by months In Viet Nam, especially in the south, as previously reported, dengue viruses were always isolated in the first quarter of the year, which consistently corresponds to the period in which DHF outbreaks did not occur (see Table 2). It is imperative to implement in this time frame active surveillance and an effective prevention programme for DHF. Year-to-year variations of dengue serotypes in Viet Nam from 1987 to 1999 During , DHF epidemics occurred in Viet Nam every year, but the two biggest DHF outbreaks were recorded in 1987 and The circulation of the dengue epidemic serotypes has been changed, as shown in Table 1. The epidemic dominant serotype of 14 was chosen as the threshold for viral activity (see Table 3). Table 1. Dengue viruses isolated from DHF patients blood during Year No. (+) / No. specimens ( +) / 548 (15.7) / 291 (2.4) / 66 (4.5) / 796 (7.0 ) / 335 (24.2) / 329 (10.6) / 268 (11.6) / 263 (20.9) (6*) / 640 (26.9) (6*) 79 (9*) 42 (16*) / (12.3) / 768 (9.9) / (20.2) / 696 (12.8) * Detected by RT/PCR Dengue Bulletin Vol 24,

3 Table 2. Dengue serotype viruses isolated in southern Viet Nam, by month, in 1998 Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Total No. isolates and serotypes 1D1 3D2 12D3 3D1 6D2 6D3 2D3 3D3 7D3 5D1 3D2 19D3 2D1 7D2 21D3 10D1 4D2 48D3 3D1 16D3 4D2 17D3 2D1 11D3 26D1 27D2 162D3 1D4 1D4 2D4 4D4 No. (+) / 17/90 15/142 2/17 3/59 7/113 27/253 30/187 62/239 19/114 22/167 15/70 0/16 219/1,467 No. specimens D1=1, D2=2, D3=3, D4=4 Table 3. The activity cycle of dengue serotype viruses in Viet Nam during Virus p: province 2 represented 91.9 of the viral isolates in 1987; 60.7 in 1990; 48.6 in 1992; and 48.5 in 1996, then decreased to 8.6 in 1998, with a continuous activity cycle of 11 years. 1 emerged post-1987 in Ho Chi Minh City and soon after in 1990, this dengue serotype spread to four provinces (Ho Chi Minh City, Dong Nai, Long An and Tra Vinh) in southern Viet Nam. In 1995, 1 was isolated from 12 provinces (11 in the south and one in the north), representing a viral activity of This activity decreased in 1997 and 1998 to 20 Dengue Bulletin Vol 24, 2000

4 11.8 and 12.4 respectively, representing a viral active cycle of 8 years from 1989 to had the lowest activity during This serotype was first isolated in 1987 in Ho Chi Minh City and Hanoi, thereafter it was found in 1991 in Ho Chi Minh City, Tien Giang and Hanoi, with a 4.9 of the viral activity. In 1995, 3 cases were confirmed in six provinces: Ho Chi Minh City, Tien Giang, Ben Tre, Vinh Long, and Soc Trang in the south and Nam Dinh in the north, representing 12.2 of the dengue activity. From 1996 to 1998, 3 activity increased to 77.8 and was found in 32 provinces, in which 15/19 are located in southern Viet Nam, 10/28 in the north, 4/11 in the central part and 3/3 provinces in the highland. This was the predominant serotype of the biggest DHF epidemic in The activity cycle of 3 decreased in 1999 to 26.9 and was only found in nine southern provinces and one province in the central part of the country. 4 was first detected in 1987 in three provinces (Hanoi, Song Be, Dong Thap), with 3.5 activity. In 1990, it was detected in Tien Giang; in 1991 in Hanoi and Ho Chi Minh City; and in 1992 in Tien Giang (Tables 2, 3). After a 4-year absence, this serotype re-emerged in three provinces in the Mekong delta: Vinh Long in 1997 and Dong Thap and Tra Vinh in In 1999, this serotype strongly increased to 25.8 and spread to seven provinces (five in the south, two in the north). This will continue to be a health threat in future years, because most children under 12 years of age have had no previous exposure to 4 virus and will thus be susceptible to 4 infection. The above data is summarized in Figure Figure 1. Year-to-year variations of dengue serotypes in Viet Nam, DEN -1 DEN -2 3 DEN -4 3 Age and sex distribution of virologically confirmed cases The age- and sex-wise distribution of positive virus isolation in north Viet Nam and south Viet Nam is given in Tables 4 and 5. Table 4. Positive virus isolation rate by age group in north Viet Nam during Age group No. cases (n = 268) Positive rate Dengue Bulletin Vol 24,

5 Table 5. Positive virus isolation rate by age group and sex in South Viet Nam in 1998 Agegroup Male Female No. (+) < (1.86) (3.73) (29.43) (30.84) (13.55) (18.22) NR (2.33) NR: not reported. Dengue viruses isolated from different age groups of patients are shown in Tables 6 and 7. In the north, the positive virus isolation rate was the highest in adults (57.84), while in the south, dengue viruses were most often discovered in children in the age group 5-14 (60.28). Characteristics of 1 isolates in Viet Nam As mentioned earlier, in southern Viet Nam, complete and incomplete virions have been isolated from patients, of which the results are shown in Table 6. Table 6. Some characteristics of 1 strains isolated in Southern Viet Nam, No. of 1 MABs of 1 Isolates 1F1 15F3 1F1+15F (Note: The MAB 1 1F1 directed against structural viral antigen; the MAB 1 15F3 directed against non-structural viral antigen.) During , we isolated 234 strains of 1 in which 134 strains had only structural antigen, 18 strains had only non-structural antigen, and 82 strains were complete virions. Concomitant infections of dengue during During , 13 concomitant infection cases caused by 2 or 3 dengue viruses were detected by IFA using MABs (see Table 7). Table 7. Cases of concomitant infection of dengue, Viruses detected by MABs No. of cases 1 & & & & & 3 & 4 1 As the number of these cases was small, we could not identify the degree of severity caused by the combination of different serotypes. Conclusion (1) The virological surveillance during offered the circulation patterns of the predominant dengue serotype by year as well as the viral activity cycle, e.g. 1, was prominent during (8 years); 2 from 1987 to 1997 (11 years) and 3 from 1996 to 1999, and this serotype is still active Dengue Bulletin Vol 24, 2000

6 emerged strongly in 1999 and will be a health threat in the future. (2) The emergence of 3 in 1995 provoked the largest DHF epidemic in 1998, and this emerging trend has been on the decrease since (3) A large dengue haemorrhagic fever outbreak will occur after a period of 3-4 years since a new serotype has been introduced. (4) Three populations of virions have been isolated from 1; one population having a structural antigen, another having only a non-structural antigen, and the third a complete virion. (5) In northern Viet Nam, dengue viruses were most often recovered in adults, while in the south, they were most often recovered in children between the age group 5-14 years. active surveillance and effective national control programme must be implemented during this period. Acknowledgements We thank Dr D. J. Gubler, Director of the CDC, Colorado, USA, for supplying us many biological products for carrying out this study. References 1. Do Quang Ha, Nguyen Kim Tien, Dinh Tuyet Hoa, Vu Thi Que Huong, Nguyen Trong Lan, Vo Dinh Tham & Nguyen Thi Hong (1989): Epidemic DHF in South Viet Nam, Dengue Newsletter, WHO, 14: Gubler DJ (1986): Application of sero-type specific monoclonal antibodies for identification of dengue viruses. Arbovirus Cultivation in Arthropod Cells in Culture. Yunker C., CRC Press, Boca Raton, 2: (6) Dengue haemorrhagic fever cases are confirmed through virological surveillance in the first quarter of every year. Therefore, it is a reminder that Dengue Bulletin Vol 24,

AVIAN INFLUENZA (A/H5N1) SITUATION IN VIETNAM, National Institute of Hygiene and Epidemiology

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