Study On Epidemiological Distribution And Influencing Factors Of Leishmania Infection In Human Population And Domestic Animals In Tanchang County, Gansu Province

Visceral Leishmaniasis, also known as kala-azar, is a vector-borne disease caused by the Leishmania species complex, which is usually transmitted by the bite of infected sandflies. In China, there have been a continuing popularity in hill-type kala-azar endemic areas, mainly in southern Gansu province and northern Sichuan province, causing a serious threat to the local population’s health status. This study was carried out in Tanchang County, Gansu Province kala-azar endemic areas, The procedure for the study includes blood sampling, questionnaire survey, simultaneous determination of geographical location, laboratory testing and statistical analysis, which aims to investigate the epidemiological distribution of Leishmania infection and the prevalent status among human population and domestic animals. It is expected to exploring the influencing factors for human Leishmania infection, in order to provide a reference for the further development of kala-azar disease control.Villages from the kala-azar endemic areas in Tanchang County, Gansu Province were selected in this study, where kala-azar cases were frequently reported. We investigated a total of 215 local people, and domestic animals including 40 dogs,12 donkeys,10 sheep and 5 pigs,5 horse,2 mules. Nested PCR detection shows the positive rate was 22.8%(49/215) in human population and 22.5%(9/40) in dogs, there were also a donkey and a horse found to be positive in the nested PCR. Among the tested population, the positive rate was 24.7%(21/85) in male,21.5%(28/130) in female, and the positive rate of people from 15 years old and under,16 to 59 years old, 60 years of age and older were 33.3%、19.1%、31.4% respectively. The products of nested PCR were sequenced and compared by NCBI Blast software, the production sequence of human and domestic animals respectively possessed a 99% and 98% similarity with Leishmania infantum. It showed that there were a large number of asymtomatic Leishmania infected people and dogs, domestic animals such as donkeys and horses also show Leishmania infection.A household-questionnaire survey and nested PCR detection for blood samples, and IBM SPSS21.0 and SAS9.3 softeare were used to analyze the influencing factors of Leishmania infection in this area. The univariate analysis represented that groups from different working-age population, different outdoor activities frequency(in summer and autumn evening), whether keep dogs, whether have livestock sheds, whether to use bed nets(in summer and autumn evening), showed different nested PCR positive rates, and the differences were statistically significant (P<0.05); multivariate logistic regression analysis showed that only two risk factors, working-age population groups and outdoor activities frequency(in summer and autumn evening) are included in the regression model. As mentioned above, non-working-age population (the children and the elderly) showed higher Leishmania infection rate, frequent outdoor activities in summer and autumn evening may increase the chances of Leishmania infection.To investigate whether the distribution of human Leishmania infection shows the characteristics familial aggregation and spatial aggregation, we apply for binomial distribution goodness of fit test and SaTScan software to analyze family GPS positioning information and laboratory test results of the family members. Results showed that the distribution of human Leishmania infection corresponded to binomial distribution without family aggregation, and neither do not conform to the spatial aggregation. The absence of familial aggregation and spatial aggregation may suggest that the Leishmania infected people randomly distributed in different families and regions.Two special primers were selected to establish a SYBR-Green quantitative PCR method in order to detect the kinetoplast DNA of Leishmania. Compared with nested PCR, which is known to be very sensitive, these two test method are highly consistent in the detection of positive human blood samples. In addition, the quantitative PCR method is more convenient and time sacing for operating. Reference gene of the relative quantification PCR is GAPDH, there is an amplification curve when human blood samples are tested, but the melting curve showed a bimodal, which indicates that nonspecific products have been amplified. Optimization of primers is needed to relatively quantify the human Leishmania infection.In conclusion, this study indicates that there are still a large number of Leishmania infected people and domestic animals. These infected domestic animals includs dogs, horse and donkeys. Non-working-age popuplation (the children and the elderly) showed higher Leishmania infection rate, frequent outdoor activities in summer and autumn evening may increase the chances for being infected with Leishmania. The distribution of local human Leishmania infection does not conform to family aggregation and spatial aggregation. In consideration of the local population and domestic animals are universally infected and are widely distributed in different families and space, their role of reservoir host in the spread of kala-azar should not be ignored, and it is recommened to be determined to in the further study.