Academic journal article Bulletin of the World Health Organization

National Dengue Surveillance in Cambodia 1980-2008: Epidemiological and Virological Trends and the Impact of Vector control/Surveillance Nationale Du Dengue Au Cambodge 1980-2008 : Tendances Epidemiologiques et Virologiques, et Impact Du Controle Des vecteurs/Vigilancia Nacional Dei Dengue En Camboya Entre 1980 Y 2008: Tendencias Epidemiologicas Y Virologicas E Impacto del Control De Vector

Academic journal article Bulletin of the World Health Organization

National Dengue Surveillance in Cambodia 1980-2008: Epidemiological and Virological Trends and the Impact of Vector control/Surveillance Nationale Du Dengue Au Cambodge 1980-2008 : Tendances Epidemiologiques et Virologiques, et Impact Du Controle Des vecteurs/Vigilancia Nacional Dei Dengue En Camboya Entre 1980 Y 2008: Tendencias Epidemiologicas Y Virologicas E Impacto del Control De Vector

Article excerpt

Background

Over the past 30 years, dengue fever has emerged as the most important arthropod-borne viral disease of humans worldwide and is a major global public health problem, primarily in the tropics. (1) Infection with one of the four serotypes of the dengue virus often produces a self-limited but painful febrile illness. The illness may be asymptomatic or can involve severe manifestations such as dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS), which may rapidly progress to death, particularly in children. To date, no drugs can cure the disease and no vaccine can prevent it. Dengue control and prevention have mainly relied on vector control and community action.

Dengue is considered endemic in Cambodia, a country with poor health and economic indicators. (2) The estimated population was 14.6 million in 2008. (3) The dengue virus was first detected in Cambodia in 1963 (4) and dengue fever has been reported through passive surveillance since 1980. Surveillance was enhanced in 2000 to include laboratory diagnosis for a sample of patients with suspected dengue and, in 2001, with the introduction of active sentinel surveillance.

This report summarizes surveillance data on dengue collected in Cambodia since 1980. Epidemiological trends were determined primarily using data from recent years. In addition, the impact of a 7-year vector control programme on the incidence of the disease was also evaluated.

Methods

Cambodia has a tropical climate, with a rainy season occurring between May and November. Rainfall typically peaks between May and June. Some 80% of the population lives in the southern and north-western parts of the country, which together contain 24 provinces and 185 districts.

National surveillance

National surveillance of dengue was established in 1980 and involved passive reporting of clinically diagnosed cases by public-sector health centres and hospitals. In 2000, virological surveillance was introduced at five hospitals, as described below. Subsequently, in 2001, the system changed dramatically when the National Dengue Control Program (NDCP) implemented sentinel surveillance based on three public hospitals and three non-profit-making private hospitals in four provinces. Cases reported through the sentinel system include those among children in either paediatric hospitals or paediatric wards in sentinel hospitals. Thus, national data collected since 2001 were obtained by both passive and active reporting of cases.

Laboratory testing

Virological and serological surveillance is carried out at three of the public hospitals that serve as sentinel sites, a non-profit making private hospital in Siem Reap and an additional public provincial hospital. Paired serum specimens are collected on admission and at discharge from hospitalized patients with clinically diagnosed dengue. The specimens are centrifuged and sent weekly in liquid nitrogen to the Institut Pasteur--Cambodia for serological, virological and molecular testing. In theory, each site should send 5-10 paired serum specimens taken from a random sample of patients with suspected dengue each week throughout the year. In reality, patients are seldom randomly selected and only two sites regularly send specimens throughout the year. The paired serum specimens are tested using an immunoglobulin M (IgM)-antibody capture enzyme-linked immunosorbent assay (ELISA) and a haemagglutination inhibition assay. Because of possible cross-reactivity, all specimens are systematically tested for anti-dengue virus and anti-Japanese encephalitis virus IgM using an in-house IgM-antibody capture ELISA and a haemagglutination inhibition assay, as previously described. (5) The first sample is tested for viral ribonucleic acid using a modified version of the reverse-transcriptase polymerase chain reaction (PCR) procedure described by Lanciotti. (6) In addition, the virus is isolated by inoculating sera into C6/36 (Aedes albopictus mosquito) and Vero E-6 cell cultures and identifying the virus serotype by using a direct fluorescent antibody assay employing monoclonal antibodies, as described elsewhere. …

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