Ha Do Quang

Huong Vu Thi Que

Khiem Ha Ba

Loan Huynh Thi Kim

Thong Dinh Quoc

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T rop. Med., 35 (4), 179-184, December, 1993 179Epidemiology of Dengue in South Vietnamand The Strategy of Its ControlHa Ba KHIEM, Do Quang HA, Vu Thi Que HUONG,Huynh Thi Kim LOAN and Dinh Quoc THONGP asteur Institute, Ho Chi Mink City, Vietnam.INTRODUCTIONDengue haemorrhagic fever (DHF) and Dengue shock syndrome (DSS) have nowbecome a major public health problem in Vietnam.In South Vietnam, DHF was first recognized in 1960 with about 60 children died. In1963, an outbreak occurred at Cai Be, Chau Doc, Hong Ngu, Tan Chau and Cao Lanh with331 clinical DHF cases and 116 deaths1.Since then, the number of DHF cases has been continuing to increase2 and recordedas the greatest one in South-East-Asia and the Western Pacific Regions3.In South Vietnam, from 1963 to 1992, DHF has occurred every year. The DHFprevalence has increased annually and major epidemic occurring every 3 to 4 years4. Inthe largest 1987 outbreak, the province which had a highest morbidity was Vung Tau :1 614/100 000 population and the province with highest lethality was Minh Hai : 12/100 000population.Large DHF epidemics in South Vietnam in 1975, 1979, 1983, 1987 occurred at thesame time with big epidemics in the whole country4.DHF cases were recorded all year round and epidemics have usually occurred fromJune to November with peak transmission in July, August and September which haveclosely related with the rainy season-the breeding period of mosquito vector.DHF patients are mostly children under 9 years old. The most affected age groupsis 5-6 years old and fewer cases occurring in adults (2.75% of DHF patients, in 1990).Contrarily to the South, the DHF morbidity in adults in the North of Vietnam washigh (53.12% in the 1983 epidemic). This is a meaningul difference between the 2 regions4.In 1979, 1983, 1987 large epidemics, the male : female mean ratio was 1.017/1. Thedifference in sex attacked by DHF in 3 large outbreaks (1979, 1983, 1987) as compared withthe remaining ones had no statistic significance (^2=1.99 with P>5%). Thus, in SouthVietnam, the sex was not a risk factor for DHF/DSS5.During 1983-1990, in Ho Chi Minh city,* The mean temperature : 27.4°C.*The relative mean humidity : 77.88%, it was 70.5-71.25% in dry seasons and 82.5180Table 1. Reported DHF/DSS cases and deaths in South Vietnam during 1975-1992Morbidity Mortality CFRYearNo. Rate/105 No. Rate/105 %1975 19,416 112.44 397 2.29 2.041976 6,151 35.62 558 3.23 9.071977 8,362 47.33 447 2.53 5.341978 17,055 94.37 484 2.67 2.831979 21,285 115.13 466 2.52 2.181980 ll,997 63.43 500 2.64 4.161981 5,933 30.66 76 0.39 1.281982 ll,281 56.99 155 0.78 1.371983 77,087 380.73 1,301 6.42 1.681984 14,562 70.30 286 1.38 1.961985 19,927 94.04 209 0.98 1.041986 15,647 72.18 243 1.12 1.551987 83,905 378.37 904 4.07 1.071988 49,237 217.04 587 2.58 1.191989 18,923 83.09 178 0.78 0.941990 41,517 174.87 298 1.25 0.711991 39,917 168.36 244 1.03 0.611992 42,363 174.75 173 0.71 0.41T able 2. Reported DHF/DSS cases and deaths in South Vietnam in comparison with the wholecountryMorbidity Mortality CFRYear Region Number Rate/105 Number Rate/105 %1975 Whole country 30, 599 76.98 417 1.04 1.36South Vietnam 19, 416 112.44 397 2.29 2.041979 Whole country 63,976 121.30 1 , 171 2.22 1.83South Vietnam 21 ,285 115. 13 466 2.52 2. 181983 Whole country 149,519 260. 60 1, 795 3. 12 1.20South Vietnam 77,087 380.73 1 ,301 6.42 1.681987 Whole country 354,517 581.96 1 ,566 2.57 0.44South Vietnam 83,905 378.37 904 4.07 1.07181Table 3. Age proportion of DHF cases in the South of VietnamAge group 1983 1984 1985 1987 1989 1990_<!! months 8.55 9.81 7.64 ll.52 10.39 8.411-4 24.90 29.65 28.71 32.43 26.77 23.ll5-9 38.97 34.90 36.23 35.70 37.95 41.3510-14 23.57 21.10 21.91 15.80 18.10 20.3415-19 3.95 4.52 3.84 3.60 4.50 4.03X20 0 0 1.64 0.95 2.27 2.75T otal No of patients 77,087 14,562 19,927 83,905 18,923 41,5179000T8000 -- HNo of cases B|HNo of deaths P^á" |||| Jfl|;Noof 5000-- J'|| |P|: *P/H P^' P«^~patients4000-- ^^H|| |||| ^p -^ .^'JiooofiilBil^3liglBlHlBlBlHlBiyio,J F M A M J J A S O N DMonthsFig. 1. Monthly distribution of the mean number of DHF patients and fatal cases inSouth Vietnam, 1983-1990.8000 -j- -$- Temperature7000 -H- Rainfall / ^-X.-A-Ae.aegypti / N.6000 -. v, Hrp ,./ X-7$-Noof patients J\ pC5000 -. / ^^^N°°f 4000.- / \patients / ^, \3000- ^/^Ö ^^^^^^v \2000 - - ^/y^^^~**^ ^\ss^^^~4k---. A-*"^*jP/ ^ A- -A---^!>-1 000 } ^^y^2^-~~-5^^ ^~^*oi ijjs H:r::::T t t t t t t t tJ F M A M J J A S O N DMonthsFig. 2. The correlation between DHF epidemics with temperature, rainfall and Aedesaegypti density, 1983-1990.182-85% in rainy seasons.*The Aedes aegypti mean density: 1.02-1.30 in dry season and 1.93-2.43 in rainyseason.Therefore, the climate and weather in South Vietnam allow continous breeding ofmosquito population. Such factors are propitious for DEN transmission that end withDHF outbreak in every year.VIRUS ISOLATIONIn the virological surveillance in Ho Chi Minh city and in some surrounding prov-inces, several DEN virus strains were isolated from patients' blood as well as from themosquitoes.In the 1987 DHF outbreak, DEN-2 was the dominant sero-type (90.5%)2. But from1990 the epidemic sero-type has changed, DEN-1 was introduced and was continuing togrow-up (58%)5. Then in 1992 outbreak, the DEN-2 was reintroduced, from 26.3% in 1991has increased to 41.4%.Of interest is that if the DEN-2 became the dominant epidemic sero-type in 1993 or1994, it is possible that a large DHF epidemic will occur.THE DHF CONTROL STRATEGY IN SOUTH VIETNAMObjectives of Strategyà" Reduction of morbidity and mortalityà"Limitation of DHF outbreaksà"Increased knowledge, attitude and practice of the community on environmental sanita-tion, mainly elimination of discarded materials.Prevention and ControlThe current option available for prevention and control of DHF epidemic is toeradicate the principal vector mosquito Aedes aegypti. Source reduction through commu-nity participation is the most appropriate method of DHF control.The basic problem is that the active prevention and control of DHF must be startedimmediately in the beginning of the silent transmission periode prior to the epidemic stageby using the effective active surveillance which based on serological, virological andclinical surveillance. These surveillances aim to provide early and precise information tothe public health service for starting the active control. Because if a DEN transmissioncan be detected early enough, an effective emergency mosquito control implementedimmediately at that moment, major DHF epidemic might be prevented.In South Vietnam the basic proofs for implementing the active DHF prevention andcontrol are based on, in the first trimester of every year :1. DHF patients have been already detected.183Table 4. The arboviruses isolated in South Vietnam during 1978-1992Number of isolates No of (+) /Nov T , , , f Sero-type of specimensYear Isolated from jjn_ HDEN- DEN- DEN- DEN- JE Chik identified1 2 3 41978 Patient's blood 1 1 2Ae. aegypti I 6+/ 69C. fatigans 11979 Patient's blood 1Ae. aegypti 1 1 10+/ 59C. fatigans 1 3 2Ae. albopictus 11980 Ae. aegypti 1 1 1 8+/ 78C. fatigans 1 3 11982 Patient's blood 1 1 3 5 12+/ 49Ae. aegyptiC. fatigans 1 11983 O/ 611984 C. fatigans 1 !+/ 461985 Patient's blood 1 !+/ 231986 O/ 501987 Patient's blood 1 48 2 2 4 not 1 58+/504done1988 Patient's blood 4 not 7+/296doneAe. aegypti 1C. fatigans 21989 Patient's blood 1 1 not 2+/ 65done1990 Patient's blood 18 10 3 not 31+/742done1991 Patient's blood 9 5 3 2 1 not 6 26+/196done contaminated1992 Patient's blood 17 12 not 29+/302doneViral isolation was not carried out in 1981.1842. Inapparent and confirmed DHF cases have been serologically diagnosed.3. DEN viruses have been isolated in this period.Only (1) and (2) are sufficient proofs to confirme that the DEN transmission hasstarted. Therefore it must be the time the Government should implement the active DHFcontrol programme. It must be emphasized and addressed to the individual responsibilityof all persons and they must be made to understand that DHF exists only because theyallow mosquitoes to breed in and around their home. Person living in communities mustbe educated to accept responsibility for their own health destiny, for their own family too.In the final part of the report, the authors stressed on the "Active surveillance" asa newstrategy for controlling the DHF epidemic in an endemic region. The goal of thisactive surveillance is to have early warning and predictive capability for epidemic dengue,based on virological and serological surveillance. As mentioned above, in South Vietnam,dengue cases were detected in January and February of every year, so the base line is asfollows : When first cases of DF/DHF were detected, it needs to be promptly implementedthe larval control and insecticide must be sprayed around the patient's houses within aradius of 100 meters.REFERENCES1 ) Thoa, N. T. K., Cuong, P. H. et Dong, N. V. (1971) : Quelques donnees sur la fievre hemorragique auSud Vietnam de 1963 a 1971. Rapport annuel sur le fonctionnement technique, Institut du Pasteur-Vietnam : 113-154.2) Ha, D. Q., Tien, N. K., Hoa, D. T., & Huong,V. T. Q. (1989): Epidemic DHF in South Vietnam, 1987.Dengue Newsletter, WHO, 14, 46-57.3) Ha, D. Q. & Huong, V. T. Q. (1990): Some data on DHF/DSS epidemic in South Vietnam, 1988.Dengue Newsletter, 15, 41-44.4) Ha, D. Q. & Tien, T. (1985): Current DHF/DSS situation in Vietnam from 1975 to 1983. DengueNewsletter, WHO, ll, 89-99.5) Ha, D. Q., Huong, V. T. Q., Loan, H. T. K. & Thong, D. Q. (1992): DHF/DSS epidemic in SouthVietnam during 1975-1990 and the strategy of its control. J. Trop. Infect. Diseases, Publ. HealthAssoc. HCM city, 4, 27-32 (in Vietnamese).6) Gubler D. J. (1987) : Current Research on Dengue. K. F. Harris (ed.). New York, Springer-Verlag3:37-56.

Epidemiology of Dengue in South Vietnam and The Strategy of Its Control

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Epidemiology of Dengue in South Vietnam and The Strategy of Its Control

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