Tawatsin, Apiwat

Thavara, Usavadee

Kyoto University Research Information Repository

TitleDF/DHF in Thailand: Current incidence and vectormanagement (Theory of Biomathematics and its ApplicationsIV)Author(s)Tawatsin, Apiwat; Thavara, UsavadeeCitation数理解析研究所講究録 (2008), 1597: 38-39Issue Date2008-05URL http://hdl.handle.net/2433/81755RightType Departmental Bulletin PaperTextversionpublisherKyoto UniversityDF/DHF in Thailand: Current incidence and vector managementApiwat Tawatsin, Usavadee ThavaraNational Institute ofHealth, Department ofMedical Sciences,Ministry ofPublic Health, Nonthaburi, ThailandDengue fever (DF) and dengu$e$ haemorrhagic fever (DHF) are caused by dengueviruses transmitted to humans through the bites of infective Aedes mosquitoes. All fourserotypes of dengue viruses (DEN-I, DEN-2, DEN-3, DEN-4) are endemic in most of thelarge cities in the Southeast Asia. The predominant virus serotypes which have beenfrequently associated with epidemics vary from country to country. The disease is now one ofthe major public health problems worldwide, especially in the tropical and sub-tropicalregions. Before 1970, only nine countries in the world got DHF epidemics, but the diseasespreads to other regions and is cunently endemic in more than 100 countries in Africa, theAmericas, Eastem Mediterranean, Southeast Asia and Westem Pacific. The Southeast Asianand the Westem Pacific have been more seriously affected nowadays. In Thailand, the firstepidemic of DHF occurred in 1958. Since then, the annual incidence of DHF (morbidity per100,000 populations) has fluctuated over time and increased from 9/100,000 in 1958 to74.8/100,000 in $2\infty 6$ , with the highest incidence of 325/100,000 in 1987. Moderately severeepidemics occurred in 1984, 1985, 1989, 1990 and 1997 whereas severe epidemics took placein 1987, 1998, 2001 and 2002. Regarding the case fatality rate (CFR) among DHF patients, itwas generally greater than 10% in the early $1960s$ . However, CFR has been reduced to lessthan 0.5% for the past 18 years. Recently, in 2004, 205 and 2006, the CFR was 0.12, 0.15and 0.13%, respectively. DHF occurs all year round with high incidence during the rainyseason. The disease mostly affects population in the age group ranging from 6 months old to15 years old, but sometimes it may affect people older than 15 years but with a minorproportion.Both species of DHF vectors: Aedes aegypti (L.) and $Ae$. albopictus Skuse are foundin Thailand. The main breeding places of $Ae$. aegypti are mostly man-made water-storagecontainers, such as earthenware jars, water-storage drums, cement tanks, ant traps, etc. $Ae$.albopictus, on the other hand, is able to breed in a wide ran$ge$ of natural and artificial types ofbreeding sources and water holding niches varying from place to place. The main breeding1597 2008 38-39 38places of $Ae$. albopictus are natural sites, such as leaf axils, tree holes, coconut husks, bamboostumps, etc., as well as, artificial containers, for example, earthenware jars, water-storagedrums, used tyres and a variety of plastic and metal containers found in the domesticenvironment.At the outset, initial vector control programs, which were implemented in late $19\infty s$,emphasized the application of chemical sprays to control adult mosquitoes, but thisintervention had littl$e$ or no impact on disease transmission. As a result, the national policy onDHF vector control was redirected to community-based strategy with emphasis on sourcereduction employing village health volunteers since the $1980s$ . The current vector controlprograms for DHF consists of provision of health education to raise public awaoeness,massive campaign of larval elimination on every Friday, epidemiological and vectorsurveillance, larval and adult control measures. Satisfactory control has been achieved insome areas, depending on the determination and the strength of local health authorities andcommunity participation. However, the programs have confronted some obstacles, $s$uch asdifficulty to mobilize community participation in larval control measures, inadequate supplyof larvicides, lack of good management in vector control program and lack of systematicallymonitoring larval and adult susceptibility to the insecticides used. More applied research isneeded to develop and implement sustainable surveillance and control programs against DHFvectors. These include identification of appropriate and effective behavior for vector controlto be encouraged in the communities, development of new and safe larvicides and their long-lasting formulations, development of early and predictive waming systems employingepidemiological, entomological and serological data, and identification of high-risk areas tobe subjected to intensive vector control using geographic information system (GIS) andmathematical models.39

DF/DHF in Thailand: Current incidence and vector management (Theory of Biomathematics and its Applications IV)

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DF/DHF in Thailand: Current incidence and vector management (Theory of Biomathematics and its Applications IV)

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