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Background: Visceral leishmaniasis (VL) was one of the most important parasitic diseases in China,caused by Leishmania protozoans and transmitted by sand flies.Recently VL cases have reappeared in China,including the extension region of the Loess Plateau.The purpose of this study was to collect fundamental data on the host-vector VL system in the Loess Plateau to assist in the development of prevention and control measures.Methods: Sand flies were collected by light traps from rural areas in Shanxian,Henan,China in 2015,as well as in Wuxiang and Yangquan,Shanxi,China in 2017.The blood sources of sand flies were analyzed by PCR detecting the host-specific mitochondrial cytochrome b (mtDNA cyt b) gene fragments.Leishmania infection in sand flies was detected by amplifying and sequencing ribosomal DNA internal transcribed spacer 1 (ITS1).The Leishmania specific antibodies in the sera of local dogs were detected by ELISA kit.Results: Blood sources showed diversity in the extension region of the Loess Plateau,including human,chicken,dog,cattle,pig and goat.Multiple blood sources within a sand fly were observed in samples from Yangquan (17/118,14.4％) and Wuxiang (12/108,11.1％).Leishmania DNA was detected in sand flies collected from Yangquan with minimum infection rate of 1.00％.The ITS1 sequences were conserved with the Leishmania donowni complex.The positive rate of Leishmania specific antibodies in dogs was 5.97％.Conclusions: This study detected the blood sources and Leishmania parasites infection of sand flies by molecular methods in the extension region of Loess Plateau,China.A high epidemic risk of leishmaniasis is currently indicated by the results as the infection of Leishmania in sand flies,the extensive blood sources of sand flies including humans,and positive antibody of Leishmania in local dog sera.Given the recent increase of VL cases,asymptomatic patients,dogs and other potential infected animals should be screened and treated.Furthermore,the density of sand flies needs to be controlled and personal protection should be strengthened.