THE SITUATION OF DENGUE HEAMORRHAGIC FEVER IN VIETNAM AND ITS MOSQUITO CONTROL STRATEGY

Ha Ba Khiem, Tran Khanh Tien, Do Quang Ha

Pasteur Institute in HCM City

Abstract

Dengue Haemorrhagic Fever (DHF) was detected in Viet Nam since 1959.

In the early stage, DHF occurred only in some districts with small numbers of cases. The largest epidemics were found in 1983 and 1987. The morbidity rates per 100,000 population in 1981 and 1987 were 41 and 462.2, respectively. The mortality rates per 100,000 population decreased from 2.7 in 1983 to 0.16 in 1994.

The morbidity rate fluctuated by region, it was higher in the Central and Southern regions than in the North. The epidemiological surveillance of some large epidemics (1983, 1987 and 1991) showed that DHF occurred in 87.2%, 58.7% and 25.9% of districts in the Southern, Central and Northern regions, respectively. The entomological data indicated that the density of Aedes aegypti was very high in these areas.

The occurrence of DHF in Vietnam obviously depends on the seasons. A study carried-out during 1991-1995 showed that DHF appeared all the year round, particularly in rainy season from June to October with the peak in August. The incidence rate of DHF correlated with the high population density of Aedes aegypti.

The age groups at risk were children under 15 years old.

The predominant viral serotypes of the 1987 epidemic was Dengue-2, followed by Dengue-1, Dengue-2, Dengue-3 in the later years with hyperendemicity.

Our studies on entomology confirmed that mosquito Aedes aegypti is the main vector of DHF in Vietnam. The entomological data in Hanoi denoted the Aedes aegypti count was from 64.8 to 83% of the total captured mosquito. The data in HoChiMinh City with Aedes aegypti count were 39.42% for adult mosquito and 96.42% for larvae collected indoors and outdoors from 1975 – 1990. The breading sites of Aedes aegypti are mostly clean water containers for domestic daily use such as jars and basins. Aedes aegypti often take meals at dawn and dusk, then stays indoors. The main resting places are clothes lines (80.54%), flower vases, and other domestic utensils.

The ULV method has been applied for vector control, but the result was limited. Therefore, it is important that to continue the studies on epidemiology and vector control of DHF. We should have the collaboration between the regional institutes and neighbouring countries. The community mobilization, the support of the government and other organizations are necessary for mosquitoes control resulting in DHF reduction.