Suwannee Adsavakulchai, Dr. Kaew Nualchawee, Prof. Shunji Murai Dr. Apisist Eiumnoh, Dr. Kiyoshi Honda
STAR Program, Asia Institute of Technology
P.O. Box 4, Klong Luang Pathumthani 12120 Thaialand
E-mail : [email protected]
Japanese Encephalities ( JE) is one of the vector-brone disease that transmitted to humans through the bite of infected vector mosquitoes that is closely associated with rice agrocosystem . in Thailand, incidence of encephalitis has been highest in the northern region. The relationship between incidence cases of JE and paddy field ( information form satellite remote sensing- JERS-1) and the others environment factors are integrated and spatially analyzed within a geographic information systems. The results of the spatial analysis along with several data sets are further for Japanese encephalitis surveillance system.
Vector-borne diseases have been the most important word wide health problems for many years and still represent a constant and serious risk to a large part of the world’s population. The major vector-borne diseases that associate with rice fields-Japanese Encephalitis, malaria and schistosomiasis- are well known, an many aspects of the vectors determine the epidemiological patterns ( Mather, 1984). A number of disease associated with rice growing have mosquitoes as the vectors. The best known and most important disease that is transmitted by mosquitoes breeding in rice fields is Japanese Encephalitis. It is transmitted mainly by Culex tritaeniorhynchus, which is often the commonest mosquito in paddy fields.
Japanese encephalitis ( JE) disease is a central nervous system ( CNS) infection caused by a flavivirus transmitted to human by Culicine mosquitoes. Pig are considered to be the main amplifying host . therefore, JE has been considered one of he most serious health problems in Asia, affecting most countries in East, Southeast and South Asia including Thailand. After the first epidemic of JE in Thailand in 1969, there were about 1,500-25,00 reported cases of viral encephalitis form 1970-1985 each year ( Suntharee, 1995) . in addition to strengthening JE disease surveillance, further studies must be conducted. Moreover, the success of JE prevention and control programs, shared information on regional epidemiology and control strategies as well as co-operation from neighboring countries are important.
This paper propose the application of Remote sensing and Geographic information System ( GIS) as tools for the study and surveillance of vector-borne disease in humans through rice agroecosystem in case of Japanese Encephalitis disease in Chiangrai Province, Thailand.
Material and method
Study site. our study focused on a portion of the northern Thailand. Chiangrai Province ( figure 1) is selected study as site because of high incidence cases of JE ( 15.4 per 100,000 in 1992-1994) form the Division of Epidemiology. Ministry of Public Health.
Figure 1: Chiangrai Province, Thailand
Mosquito Vector sampling . two village were randomly selected form the area that have paddy field and pig farms. Sampling site is in Ban Juai Khrai and Amphoe Chiang Sean ( fig 2). Mosquito abundanc data were collected using Nozawa light-Trap every month form 6:00 pm. Until 6:00 am . the following morning in 1992 ( courtesy from the division of Medical Entomology, Department of Medical Science. ).
Figure 2: Study area in from JERS-1 (courtesy from NASDA). In square box is the sampling site.
Environmental condition. in the study area the climatic conditions were recorded such as temperature humidity and precipitate form the Department of Meteorology, Ministry of communication. Classification of mosquito. Entomologist form the Division of Medical Entomology, Department of Medical Science classified the mosquito for culex triaeniouthynchus that the commonest in paddy field and related to JE are Culex gelidus and culex fuscocephala ( fig. 3) .
Figure 3: Encephalitis Vector Mosquitoes
Landscape map generation. A major component of this study was the sue of remotely-sensed data to identify and map the landscape elements within the study area, with particularly emphasis on those elements that already associated with mosquito abundance ( i.e., pasture and paddy field as shown in fig 2). A computer-generated map of landscape elements was created with digital JERS-1 scene ( curtsey from NASDA ) acquired on December 15, 1993. JERS -1 picture element ( pixel ) represents approximately 18×24 m. on the ground. The classification algorithm, which assigned pixels to categories based on their spectral reflectance characteristics, utilized JERS-1 VNIR ( Visible and Near Infrared Radiometer ) Band -( 0.52-0.60mm) Band 2( 0.63-0.69mm). the landscape elements identified using JERS-1 data were Dense forest, Plantation, Paddy field and water body. The classification with the actual land cover, as interpreted using field survey. Results
The average temperature is 22-290C in 3 years in the northern region of Thailand. And the precipitate occurs with high precipitate in June-August. The correlation between mosquito abandance data and precipitate is 0.9116 as shown in fig .4. the most type of mosquitoes are related to JE about 63.7-93.2% of total mosquitoes. In Chaingrai Province, the density of mosquitoes is maximum in July and Culex triaeniorhynchus is the dominant species that very high potential for vinous to grow. In addition, no dynamic of JE vector mosquitoes that are the high peaks of vector found in July for 3 consecutive years ( fig 4). However, the density of vectors decrease every year that the average number of maximum in 1992, 1993 and 1994 are 12,050 ( July ), 7,443 ( July ) and 896 ( July ) mosquitoes per trap per night respectively. The relationship between the density of JE vectors and number of JE case rates that are including rainfall, temperature and humidity during 1992 shown in fig 5.
Figure 4: the correlation between mosquito abandance data and precipitate
Fig 5: The relationships between the density of JE vectors and No. of JE case rates that are including rainfall. Temperature and humidity during 1992.
During 1981-1994, the incidence cases of JE in Thailand are 700-2,084 per year respectively. The case rates decreased in 1986 but in the northern regions was still higher than the other regions in Thailand. The reason that the northern part was the highest because the influence of environmental factors and the others such as the climatic condition, misquote density, potential of vectors and population’s immunity. The suitable temperature for JE virus growth in mosquito is equal to or more than 280C ( Mogi, 1975). And occurrence of JE outbreaks consistently corresponds with paddy field cultivation in the rainy season. In addition, culex traeniorhynchus is a dominant species that is the highest potential vectors of JE disease, feeding mainly on pigs . Pigs are raised in large numbers in northern Thailand reflected secular amplifying hosts. However, the reduction of JE cases in the northern Thailand reflected secular changes, such as modification in land utilization and increasing urbanization, that have concurrently led to a gradual declined in risk. According to9 the vacination program may be decrease the JE case rates that is not true because the case decrease before vaccine program begin. The vaccine program started in 1987 but the cases decrease in 1986. it can be concluded that the JE cases decreased because the density of JE vector mosquitoes decreased.
There are no dynamic of Japanese encephalitis mosquitoes for 3 consecutive years during January 1992 to December 1994 in Chiangrai Province. Several environment variables may have sufficiently high correction values with mosquitoes abundance to provide a basis for forecasting population densities , including type of potential mosquitoes, density of mosquitoes. For further study, I will be developed model for surveillance of vector-borne disease in Humans Through Rice Agroecosystem in case of Japanese encephalitis disease in Chiangrai Province, Thailand.
This report was sponsored by the Japanese Government Project regional Education and Development Program ( REDP)- Education Program (b).
I am also extremely grateful to the Division f Medical Entomology, Department of Medical Science, Ministry of Public Health for available information. Their wholehearthed supported and enthusiasm of this activity are grateful acknowledged.
I would like to thank my examination comities for their helpful comments and suggestion.
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