Research On The Epidemiological Characteristics And Impact Factors Of Visceral Leishmaniasis In The Kezile Drainage Area

Xinjiang Uygur Autonomous Region is among the Visceral Leishmaniasis (VL) endemic areas in China, where the disease is most serious in4counties along the Kezile River, i.e, Kashi, Shufu, Shule and Jiashi. As one of the neglected tropical diseases (NTD), VL represents2types, anthroponotic VL (AVL) and desert sub-type of zoonotic VL (DST-ZVL) in the region. A lot of efforts were made on classification of the vector, namely sandfly, geographical distribution and ecological researches on sandfly. Nevertheless, large gaps still remain in the nature of epidemiology, transmission of VL, as well as molecular biological research on sandfly. In recent years, the advance of spatial statistics and molecular biology have allowed for deepening our understanding on the epidemiology and the genetics of sandfly population from a newly different view.In the study, monthly data were collected from the4counties, including epidemiological, demographic, geographic, and environmental data. Sandflies were collected from some of those townships. Spatio-temporal clustering, evolution on hot spots of VL incidence, and environmental impact factors of VL, in addition to sandfly population genetic structure were studied through epidemiology, spacial statistics and molecular biology. Main outputs are presented as follows.1. Spatio-temporal clustering analysis of VLBased on scan statistic, a total of16VL spatial clusters by township by year were obtained (P<0.01), which could be classified as2most likely significant clusters and1significant secondary cluster. Spatio-temporal clustering analysis in13consecutive years resulted in2high risk clustering zones with the corresponding high risk time frames. It showed VL risk in the2clusters was27.45and29.09 times higher than that other zones with the same population radius and time interval (P<0.01).2. Evolution of hot spot of VL incidenceCorrelativity of geographic region showed the score of Global Moran’s/and Z value was0.18and3.89(P<0.01), the Local General G and Z value was0.59and4.11(P<0.01), respectively. It indicated that VL distribution was of high spatial autocorrelation with high-high clustering. By using geostatistical analysis, prediction map was illuminated and hot spot analysis was conducted. In general,80hot spots were identified, which showed medium or highly clustering of VL incidence in some certain areas. In addition, the distribution of hot spots showed a moving tendency of middle-east-middle in geography, while the disease distribution showed a tendency of AVL-DSTZVL-AVL with obvious variations of hot spots over time.3. Environmental impact factors of VLBased on correlation analysis and the multivariable linear regression model, environmental variables relevant to the incidence of VL were screened to set up the disease-environment model for different VL types. The impacts of certain environmental factors on VL incidence were then quantified. Two models for AVL (see①) and DST-ZVL (see②) are described as follows.①INCIDENCE=-8.64+0.35QTM6Z8+9.46QEM6Z8-0.06QRM1Z3R2=0.61,F=12.67, P<0.01.②INCIDENCE=-16.05+0.29T6+0.82QTMYEAR-0.21QRM1Z3R2=0.34, F=4.13, P<0.05.4. Molecular population genetic structure of sandflyMolecular population genetic structures of Phlebotomus wui and Phlebotomus Longiductus were studied by using mtDNA-Cytb. Results showed the lowest FST was in the P. Longiductus population while the highest was among both two species. The negative FST of P. wui indicated minor genetic difference among this population. The level of gene flow of P. wui (R2=0.34, P<0.05) and P. Longiductus (R2=0.09, P<0.05) showed negatively relative with geographic distance, and the pattern of population genetic structure was in accordance with isolation-by-distance model.