Study On The Relationship Between Geographical Landscape Features And Plague Occurrence In Yulong Plague Natural Focus

ObjectivesNatural plague focus of wild small mammals in Yulong county was confirmed in2006.The epidemic situation of plague is still active in this area currently,but there is no systematic research on the relationship between the geographical features and plague occurrence.This study aims to investigate the distribution and features of geographic landscapes,to analyze the relationship between it and small mammals,parasitic fleas and Yersinia pestis in Yulong plague focus,and to explore impacts of geographic landscape factors on plague occurrence for preventing and controlling the occurrence and epidemic of plague effectively.Methods1.Study sites and objects: Four altitudinal gradients were selected in Wenbi mountain and 3 research samples were selected in each altitudinal gradient.Study was conducted follow the 4 seasons in a year.2.Small mammals and parasitic fleas collection: Small mammals were captured by snap trap method,200 traps at least were placed in each elevation.Small mammals were checked in the morning and were brought to laboratory for identification and counting.Parasitic fleas were collected by comb method and stored in micro-centrifuge tube with 75% ethanol at room temperature,then identified and counted through microscope.3.Tissue materials collection: Liver and spleen were extracted from the body of small mammals,and were stored in micro-centrifuge tube under the condition of-20℃.4.Geographic landscape data collection: Geographic landscape data were collected in the wild(including latitude and longitude,altitude,temperature,air humidity,water,soils,vegetation and crop types).Climate data of Lijiang meteorological station from 2005-2016 were purchased through Resources and Environment Data Cloud Platform.A part of data were also reviewed via Chinese and English databases,internet document resources and book resources.5.Laboratory test: Yersinia pestis in liver,spleen,water and soil samples were isolated by selective medium,and the F1 antigen of Yersinia pestis was detected through GICA.6.Data management and analysis: All data were managed by Excel 2010,and the geographical landscape database was established by map-making in ArcGIS10.0software.Results1.Topography: The topography of Yulong plague focus was tilted from northwest to southeast edge.Most of this area were dominated by the landscape of middle mountains and valleys,high mountains and canyons were belongs to the northeast area.There were developed a number of Bazi,among which the small and middle sized basins are the most typical Bazi in this area.2.Climate: The climate was belongs to semi-humid climate regions and low-latitude mountain monsoon climate in south temperate zone.The average month temperature was 13.6℃ from 2005 to 2016,and the hottest month were from May to August per year(17.7-19.4℃),the coldest month were from December to the next January(7.1-7.3℃).The relative humidity was 59.4% per month,and the highest month were from July to September(78.2-79.8%),the lowest were from January to March(41.1-43.3%).The average rainfall was 884.5mm per year,which concentrated mostly on June to September,which accounts for 80.4% of the whole year,rainfall from November to the next April was low,accounts for 4.8%.From July to September,the monthly sunshine hours were the lowest(115.8-134.6 hours),and the highest fromDecember to the next January(251.6-262.0 hours).As a whole,the change of temperature is relatively smaller in a year while larger between each month.The precipitation varies greatly in different seasons,showing a significant difference between the dry and rainy season.The trend of sunshine hours and precipitation were basically opposite.3.Soils: The soils of Yulong plague focus belongs to 2 classes,5 subclasses and 5types,including yellow-brown earths,brown earths,dark-brown earths,and a small amount of red earths and brown coniferous forest soils.The soils were characterized by vertical distribution along with altitude gradients,different types of soil have different development processes and structures.4.Vegetations: There were developed 5 vegetation groups in this area,including needle leaf forest,mixed needle leaf and broadleaf forest,broadleaf forest,scrub and cultural vegetations.Vegetations were characterized by vertical distribution along with altitude gradients obviously,which form different landscape belts.5.Hydrology: Water resources were abundance in Yulong plague focus and the surrounding areas,mainly including the surface water resources(such as rivers,lakes,pools,reservoirs)and ground water resources.Precipitation and evaporation are the important factors in the balance of water ecology system.6.Small mammals: A total of 884 small mammals were captured,the general density was 17.98%.The number of Apodemus chevrieri(146)and Eothenomys miletus(66)were highest in autumn,and Eothenomys proditor(34)was highest in winter.At the altitude distribution,the number of small mammals was increased with the altitude,Apodemus chevrieri and Eothenomys miletus were dominant species in Yulong plague focus,and Eothenomys proditor only acted as dominant species at an altitude of 3000 m above.7.Parasitic fleas: A total of 484 parasitic fleas were captured,the number of it were highest in winter(198)and lowest in autumn(85).The number of Neopsylla specialis specialis(52)and Ctenophthalmus quadratus(48)were highest in summerand spring respectively.At the altitude distribution,the number of fleas was increased with the altitude,Neopsylla specialis specialis and Ctenophthalmus quadratus were acted as dominant species in the altitude of 3000 m above.8.Yersinia pestis: There were no positive results in the selective culture and plague F1 antigen test of 880 liver samples,873 spleen samples,218 soil samples and26 water samples.A total of 12 Yersinia pestis were isolated and 4 of them were collected from April to May in the 3 consecutive years from 2006 to 2012,and all of12 Yersinia pestis were detected in the Luzi village,Huangshan town,Yulong county.Conclusions1.Bazi is a kind of particular landform in Yulong natural plague focus,plague occurrence and epidemic has been affected by the natural environment conditions in Luzi village and the surrounding areas.2.This area belongs to semi-humid climate regions and low-latitude mountain monsoon climate in south temperate zone,climate elements such as wet water conditions and temperature were closely related to the seasonal change of plague,which can be considered as one of the early warning indicators of plague occurrence and epidemic.3.The soils of Yulong plague focus mainly including yellow-brown earths,brown earths,dark-brown earths,and a small amount of red earths and brown coniferous forest soils.The soils shows a characteristic of vertical zonal distribution with elevation.4.Vegetation of Yulong plague focus core area was mainly scrub.Cultivated lands were distributed in valleys and low-lying areas.Scrub and cultivated lands intersect each other,which become vital habitat of Apodemus chevrieri,Eothenomys miletus,especially Eothenomys proditor.