Dengue

Fact sheet

Key facts

• Dengue infection in Viet Nam is unstable but peaks in June to October annually. Dengue morbidity per 100,000 population increased steadily from 32.5 in the year 2000 (24,434 cases) to 120.0 in 2009 (105,370 cases), and was 78.0 in 2011 (69,680 cases).
• Over 85% of all dengue cases and 90% of all deaths due to dengue occur in the southern provinces of Viet Nam. Some 90% of dengue deaths are seen in people under the age of 15 years.
• Viet Nam has been successful in controlling dengue fever mortality. Since 2005, mortality is less than 1 per 1000 cases. However, Viet Nam has been less successful in reducing the number of dengue cases.
• Almost all cases and deaths occur in the southern region of Viet Nam. For the period from 2001 to 2011, 76.9% of cases and 83.3% of deaths occurred in 20 provinces in the south.
• Dengue epidemics usually occur in three to five year cycles.
• Viet Nam’s National Dengue Control Programme (NDCP) was established in 1999, and Government funds allocated for this programme range from $1 million to $5 million per year (contribution from local government funds are excluded).
• The NDCP is based at the General Department of Preventive Medicine, Ministry of Health (MoH) and eight national and regional institutions participate in the programme.

The situation

• The main factors responsible for the emergence and re-emergence of dengue are:
• High density of the dengue vector and wide geographic distribution of the vector, and circulation of all four type of dengue virus. In Viet Nam a lack of a reliable water supply in rural areas and substandard housing, plus inadequate water supplies and waste management systems in rapidly expanding peri-urban areas, means that people have to store water in or near to their homes. This supports increasing dengue vector density.
• The epidemiological situation is worsened by the failure of health systems to maintain adequate control of the spread of Aedes aegypti.

Diagnosis

• Diagnosing dengue is not simple at district level, almost all cases are diagnosed clinically. Around 15-20% of dengue cases are serologically diagnosed and in 3-5% cases virus isolation is performed.
• All four dengue serotypes are isolated annually but the contribution of each to the proportion of total cases varies from year to year.
• Dengue diagnosis has improved, but better tools for an early, rapid, specific, sensitive, and non-expensive diagnostic tools, such as rapid diagnostic tests, are needed.

Control

• The most common control strategy used to date has been a vertical top-down approach using house-to-house inspections, insecticide spraying and treatment of water containers where mosquitoes breed, and community education.
• Because dengue mosquitoes breed primarily in water containers, it is relatively easy to target these for vector control, particularly through elimination of discarded containers which provide breeding sites for the vector.
• Dengue control programme has piloted several models for community-based vector control – such as:
• the use of Mesocyclops (a copepod crustacean) in community-based biological control programmes, Mesocyclops are placed into water containers to eat larvae..
• providing guppy fish to school children who then place the guppies in water containers at home.
• establishment of a dengue collaborator networks in hyper-endemic communities.

WHO's response

• Supporting MoH to develop a national strategy for dengue control and prevention;
• Providing technical and funding support for training courses for dengue case management at provincial level;
• Providing technical support to develop dengue monitoring and evaluation indicators for national dengue control programmes;
• Providing technical support to improve surveillance and reporting of the epidemiological situation;
• Supporting the annual celebration of the Association of Southeast Asian Nations (ASEAN) Dengue Day.