Dengue Epidemic in Southern Vietnam, 1998.A widespread epidemic of dengue dengue /den·gue/ (den´ge) an infectious, eruptive, febrile, viral disease of tropical areas, transmitted by Aedes mosquitoes, and marked by severe pains in the head, eyes, muscles, and joints, sore throat, catarrhal symptoms, and sometimes a skin eruption and painful swellings of parts. hemorrhagic fever (DHF DHF - Abu Dhabi Al Dhafra Military Airport (airport code) DHF - Dansk Håndbold Forbund DHF - Data Handling Function DHF - Decoupled Hartree-Fock DHF - Demand History File DHF - Dengue Hemorrhagic Fever DHF - Design History File DHF - Diluted Hydrofluoric Acid DHF - Document History File) occurred in southern Vietnam in 1998, with 438.98 cases/100,000 population and 342 deaths. The number of DHF cases and deaths per 100,00,3 population increased 152.4% and 151.8%, respectively, over a 1997 epidemic. Dengue viruses were isolated from 143 patient blood samples; DEN-3 virus was identified as the predominant serotype, although a resurgence of DEN-4 was noted. Since 1963, the incidence of dengue hemorrhagic fever (DHF), a leading cause of hospitalization and death in children, has steadily increased in Vietnam. In 1998, a widespread DHF epidemic affected 19 provinces in southern Vietnam (Figure 1); 119,429 cases of DHF and 342 deaths were reported (Figure 2); and the rates per 100,000 population were 438.98 and 1.243, respectively, for a case-fatality rate of 0.29%, an increase of 152.4% and 151.8%, respectively, over those of a 1997 epidemic (288.02 and 0.83)(1). The epidemic curve was similar to those of previous years: cases increased substantially from June to November (1-4). Peak transmission occurred from July to September, closely associated with the rainy season, a breeding period for the mosquito vector. DHF cases were reported in the first quarter in Ben Tre (1,387.2/2.4/100,000), Binh Phuoc (635.1/0), and Kien Giang provinces (568.4/2.9). [Figure 2 ILLUSTRATION OMITTED] We describe epidemiologic, virologic, and serologic studies carried out during the epidemic. The Study Reports of DHF cases and deaths were gathered by hospitals and Departments of Hygiene and Preventive Medicine at the district level, then sent to the Provincial Centers of Preventive Medicine. These data were reported weekly to the Pasteur Institute in Ho Chi Minh City Ho Chi Minh City, formerly Saigon, city (1997 pop. 5,250,000), on the right bank of the Saigon River, a tributary of the Dong Nai, Vietnam. Ho Chi Minh City is the largest city, the greatest port, and the commercial and industrial center of Vietnam. It has an airport and is the focus of the country's highways, railroads, and Mekong delta waterways. An ancient Khmer settlement, Saigon passed (17th cent.) to the Annamese.. Seventeen of the 19 provinces submitted blood samples to the Institute for virus isolation. One hundred forty-three dengue viruses were isolated from 1,236 blood samples, for a positivity rate of 11.6% (Table 1). Although DEN-1 and DEN-2 had been the most common serotypes (1-4), DEN-3 was isolated in 15 provinces.
Table 1. Dengue viruses isolated, by province, 1998
No. Prov. Jan Feb Mar Apr
1 Lam Dong 2D3
2 Dong Nai
3 Binh Phuoc
4 Binh Duong
5 BR-V Tau
6 HCMC 2D3 1D3
7 Tien Giang
8 Dong Thap 1D4
9 Vinh Long 2D1
6D2
3D3
10 Tra Vinh
11 Can Tho
12 Soc Trang
13 Ben Tre 1D1 1D1
1D3 2D3
14 An Giang 1D2 1D3
1D3
15 Bac Lieu
16 Ca Mau
17 Kien Giang 2D2
8D3
Total 1D1 3D1 3D3
3D2 6D2
12D3 6D3
1D4
No./No. specimens 17/90 15/142 0/10 3/57
Prov. May Jun Jul Aug
Lam Dong 2D3 1D3 5D1
5D3
Dong Nai 1D2 1D2
1D3
Binh Phuoc 1D3
Binh Duong
BR-V Tau 1D1
HCMC 2D3 2D3 2D3
Tien Giang 1D1 1D1 4D3
5D3 1D2
Dong Thap
Vinh Long 1D2
Tra Vinh 1D1
4D2
1D3
Can Tho 1D3 1D3
Soc Trang 1D1
5D3
Ben Tre 2D3 3D1 1D3
8D3
An Giang 1D3
Bac Lieu 1D3 1D3
Ca Mau 1D3
Kien Giang
Total 5D3 5D1 2D1 6D1
2D2 6D2 19D3
18D3 17D3
No./No. specimens 5/103 25/244 25/179 25/104
Prov. Sep Oct Nov Dec Total
Lam Dong 5D1
10D3
Dong Nai 1D2 3D2
3D3 1D3 5D3
Binh Phuoc 1D3
Binh Duong 2D3 2D3
BR-V Tau 1D1
HCMC 2D3 7D3 18D3
Tien Giang 3D2 2D1
1D3 4D2
21D3
Dong Thap 1D4
Vinh Long 2D1
7D2
3D3
Tra Vinh 4D3 2D4 1D1
1D4 4D2
5D3
Can Tho 2D3
Soc Trang 1D1
5D3
Ben Tre 5D1
14D3
An Giang 1D3 1D2
4D3
Bac Lieu 2D3
Ca Mau 1D3
Kien Giang 2D2
8D3
Total 2D3 4D2 4D3 17D1
15D3 2D4 21D2
1D4 101D3
4D4
No./No. specimens 2/78 20/161 6/53 0/15 143/1,236
Dengue virus serotypes: D1 = DEN1; D2 = DEN2; D3 = DEN3; D4 = DEN4 The blood samples were obtained on days 1 to 4 after the onset of illness and were stored at -20 [degrees] C or -70 [degrees] C before being injected into C6/36 (Aedes Aedes /Ae·des/ (a-e´dez) a genus of mosquitoes, including approximately 600 species; some are vectors of disease, others are pests. It includes A. aegyp´ti, a vector of yellow fever and dengue. A·e·des ( albopictus) cell cultures seeded at 3 x [10.sup.5] cells per mL in 1-mL glass tubes. Undiluted blood was injected into duplicate tubes (0.05 mL per tube) and incubated at 28 [degrees] C for 7 days. Infected cell cultures were harvested and assayed for dengue virus by the direct and indirect fluorescent antibody techniques, with the monoclonal antibody SLE 6B6C-1/FITC FITC - Faculty Instructional Technology Center FITC - Fishery Industrial Technology Center (University of Alaska Fairbanks) FITC - Fluorescein Isothiocyanate FITC - Foundation for International Technological Cooperation (Washington, DC) conjugate and four serotype-specific monoclonal antibodies: DEN-1 (Hawaii 15F3-1-15 and D2-1F1-3), DEN-2 (NGC 3H5-1-21), DEN-3 (H87 5D4-11-24), DEN-4 (H241 1H10-6-7), and Japanese encephalitis (Nakayama 14H5) (5). To detect dengue-specific IgM antibody, samples were tested by IgM-capture enzyme-linked immunosorbent assay (Mac-ELISA) by using the monoclonal antibody SLE 6B6C-1/HRP conjugate (6). Sixteen of 19 provinces in southern Vietnam submitted patient sera for dengue serodiagnosis. Seropositive results were seen in all provinces throughout the year, and the confirmation rates increased during the DHF season (Table 2). Despite the high sensitivity and specificity of Mac-ELISA for dengue diagnosis, the seropositivity rates in eight provinces were low ([is less than] 50%). Clinical diagnoses of DHF during the epidemic in these provinces may have been overestimated, especially in cases of suspected DHF or fever of unknown origin. As a result, hospitals in these provinces were overwhelmed by patients, to the extent that the quality of treatment has been affected.
Table 2. Specimens positive for dengue virus, by province, 1998
Prov Jan Feb Mar Apr
Lam Dong 0(*)/10
Dong Nai
Br-V Tau
HCMC 9/38 35/82 6/23 20/48
Long An 0/38
Tien Giang
Ben Tre
Vinh Long 17/98
Tra Vinh
Dong Thap 3/5 1/3 1/5
Can Tho 2/3 1/2
Soc Trang
An Giang 28/118 25/101 45/138 51/117
Ca Mau
Bac Lieu 1/2
Kien Giang 1/17 0/5
Total 41/178 77/324 54/167 74/184
Prov May Jun Jul Aug
Lam Dong 3/10
Dong Nai 18/22 4/4
Br-V Tau 2/2 4/4
HCMC 14/21 38/54 78/117 71/79
Long An 16/24 6/7
Tien Giang 1/6 23/67
Ben Tre 9/14 25/32 16/21
Vinh Long 41/57
Tra Vinh 19/27 5/6
Dong Thap
Can Tho 11/17
Soc Trang 1/2 8/28
An Giang 72/116 55/68 62/86 88/114
Ca Mau 6/7 8/12 1/6
Bac Lieu 3/11
Kien Giang 0/7
Total 119/202 201/306 194/285 194/255
Total
& rate
Prov Sep Oct Nov Dec (%)
Lam Dong 3/20
(15)
Dong Nai 12/16 34/42
(80.95)
Br-V Tau 6/6
(100)
HCMC 40/83 63/162 24/54 16/66 414/827
(50.06)
Long An 2/3 24/72
(33.33)
Tien Giang 6/8 4/4 10/10 3/3 47/98
(47.96)
Ben Tre 12/26 3/3 65/96
(67.71)
Vinh Long 58/155
(37.42)
Tra Vinh 10/17 5/6 39/56
(69.64)
Dong Thap 3/4 8/17
(47.06)
Can Tho 14/22
(63.64)
Soc Trang 9/30
(30)
An Giang 50/88 37/60 26/38 3/4 542/1,048
(51.72)
Ca Mau 9/12 4/4 28/41
(68.29)
Bac Lieu 4/13
(30.77)
Kien Giang 11/13 0/1 0/1 12/44
(27.27)
Total 123/229 144/276 64/107 22/74 1,307/2,587
(50.52)
(*) Number of positive specimens/total number of sera tested by IgM capture enzyme-linked immunosorbent assay (Mac-ELISA) Conclusions During 1990-1998, dengue viruses were most often recovered in children 5 to 14 years of age (3). In the 1998 outbreak, more dengue viruses were isolated from adults (18.2%) than in the previous 4 years. Adults are not likely to have been exposed to the emerging DEN-3 virus. From 1987 to 1998, the dengue virus serotypes in circulation changed (3). DEN-2 was responsible for the 1987 epidemic. From 1990 1;o 1995, DEN-1 predominated, but had decreased t;o 11.9% by 1998. DEN-2 accounted for 42.2% of the serotypes identified in 1997, but had decreased 1;o 14.7% by 1998. The circulation of DEN-3 was the lowest during 1987-1994; increased to 29.5% by 1996, 42.2% by 1997, and 70.6% in 1998; and was the predominant serotype of the 1998 epidemic. DEN-3 virus was first detected in 1987 only in Ho Chi Minh City, but by 1991 it was also identified in Tien Giang Province (7). In 1994 it appeared in Tien Giang and Soc Trang, in 1997 in four additional provinces, and by 1998 in 15 provinces. After a 5-year absence, DEN-4 virus was also detected in Dong Thap and Tra Vinh provinces in the Mekong Delta. During a 1998 DHF epidemic affecting 19 provinces in southern Vietnam, 119,429 cases and 342 deaths were reported, for an increase of 152.4% and 151.8%, respectively, over 1997. It was the largest DHF epidemic in Vietnam since 1963. DEN-3, which began to emerge in southern Vietnam in 1994, was the serotype associated with the 1998 epidemic. The simultaneous emergence of DEN-4 should alert public health officials to the potential for outbreaks associated with that serotype. Virologic and serologic surveillance indicate that dengue is endemic in southern Vietnam and that the Dengue Control Program should be implemented in the interepidemic phase--in the first quarter of every year. Acknowledgments We thank D.J. Gubler for providing the monoclonal antibodies used in this study. Dr. Do Quang Ha is Head of the Arbovirus ar·bor·vi·rus (är  b r-)n. Laboratory, Pasteur
Institute, Ho Chi Minh City, Vietnam. His research interests focus on
arboviruses and the infectious diseases they cause.References (1.) Do QH, Vu TQH, Huynh TKL, Cao MT. Dengue activity in southern Vietnam, 1995-1997. Journal of Medicine and Pharmacy Activity III 1998;special issue:259-63 (in Vietnamese). (2.) Do QH, Nguyen KT, Dinh TH, Vu TQH, Nguyen TL, Vo DT, et al. Epidemic DHF in South Vietnam, 1987: epidemiological and virological studies. Dengue Newsletter (WHO) 1989;14:46-57. (3.) Do QH, Vu TQH, Huynh TKL, Dinh QT, Deubel V. Dengue haemorrhagic fever in the south of Vietnam during 1975-1992 and its control strategy. Jap Trop Med 1994;36:187-201. (4.) Do QH, Vu TQH, Huynh TKL, Pham KS. Situation of DHF in South Vietnam, 1991-1994. Dengue Bulletin WHO 1996;20:55-61. (5.) Gubler DJ. Application of serotype-specific monoclonal antibodies for identification of dengue viruses. In: Yunker C, editor. Arboviruses in arthropod cells in vitro. Boca Raton: CRC Press; 1986. p. 3-14. (6.) Kuno G, Gomez I, Gubler DJ. Detecting artificial anti-dengue IgM immune complexes using an enzyme-linked immunosorbent assay. Am J Trop Med Hyg 1987;36:153-9. (7.) Do QH, Vu TQH, Huynh TKL, Cao MT. Virological surveillance of dengue haemorrhagic fever in southern Vietnam during 1987-1998. Vietnamese Journal of Preventive Medicine IX 1999;3:17-27 (in Vietnamese). Do Quang Ha, Nguyen Thi Kim Tien, Vu Thi Que Huong, Huynh Thi Kim Loan, Cao Minh Thang Pasteur Institute, Ho Chi Minh City, Vietnam Address for correspondence: Do Quang Ha, Pasteur Institute, 167 Pasteur Street, District 3 Ho Chi Minh City, Vietnam; fax: 84-8-8231419; e-mail: pvtu@netnam2.org.vn. |
|
||||||||||||||||||||
Printer friendly
Cite/link
Email
Feedback
Reader Opinion