Geographic Information of Helminthiasis in Thailand

要旨

Helminthiasis, including Opisthorchiasis viverrini (liver fluke) and Necator americanus (hookworm), is still a significant public health problem among high risk occupations and groups in Thailand. Endemic infections are closely related to socio-economic status and risk behaviors for parasitic infections among villagers in rural and remote areas. Currently, the helminthiasis control program managers have set up the national plan to prevent and control these diseases by the interaction and responses of the provincial public health offices. However, the program managers need to have information determined by evidence based needs. These data are representative of all age groups in Thailand and date are derived from the nationwide household survey. The prevalence of Opisthorchis viverrini (liver fluke), Necator americanus (hookworm), and other helminthes in this study was evaluated in 75 provinces during the period from January to May 2009. A total of 15,555 stool specimen samples were obtained from the population by using 30 cluster random sampling under WHO guidelines. The Formalin Ether Concentration technique was applied to the fecal samples. The objectives of the study were: 1. to evaluate a GIS health model by using spatial analysis to investigate the prevalence of O.viverrini and hook worm infections in relation to the sea level and geographic positions in high risk areas, and 2. to analyze the factors that correlate with infections among rural Thai people. Logistical regression with an analysis of the determinant factors was used to correlate the prevalence of O. viverrini with the geographic information as determined by GIS. The result of this large scale survey showed the overall prevalence of helminthiasis among these selected groups of Thai people was 18.1%. The highest prevalence of O. viverrini was 85.3% at a village in Sri Sa Ket, in the Northeast region. This village is located in the Non Sung district at latitude 14°36'11" N and longitude 104°24'1" E, at an attitude of 161 meters above mean sea level. There, the mean rainfall was 246.2 cm per year, and the mean temperature was 28.2°C. In the Northeast region, the study results showed a correlation between a high prevalence of O. viverrini and geographic information regarding land use. The results indicated that land use of paddy fields with loam soil type was correlated with a high prevalence of O. viverrini. including mean rainfall measured per year, Residential land use with clay soil type also correlated with a high prevalence of O. viverrini infections among people in the northeast. In contrast, in the northern region, a high prevalence of O. viverrini infections was associated with GIS geographic information of orchard and forest land use with organic soil type. In the north, 80% of the land area is composed of forest and high hills. This is an important area for the fountainheads of rivers, and many species of natural freshwater fish are present. These support parasitic infections, and in turn those people who consume uncooked, freshwater fish. Frequent consumption of raw or uncooked fresh water fish is the main cause of O. viverrini infections among people in the north. However, in the southern region, the presence of hookworm and Strongyloides stercoralis (pinworm) showed a geographical heterogeneity with the highest prevalence occurring in regions with clay and mountain soil types.There were also statistically significant factors which influenced and correlated with O.viverrini infections. These included: 1. the consumption of raw fresh water fish (p-value<0.000) and 2. defecation in proper latrines as opposed to defecation outside of latrines or in unsanitary toilets (p-value<0.001). The strongest fit predictor for O.viverrini infections was the consumption of raw fresh water fish which had a 58.94% predictive value. In conclusion, the study results showed a high prevalence of liver fluke and hookworm infections associated with health behaviors and Geographical Information Systems. These results demonstrate that spatial analysis can help to identify patterns of high risk for O. viverrini (liver fluke), Necator americanus (hookworm) and Strongyloides stercoralis (pinworm) in order to facilitate prevention and control.