New records of spotted fever group rickettsiae in Baltic region

Tick-borne rickettsiae are considered to be emerging, but there is still a lack of data on the occurrence and prevalence of the spotted fever group rickettsiae across Europe, especially in the Baltic countries. The aim of the present study was to investigate the presence of Rickettsia spp. in Dermacentor reticulatus and Ixodes ricinus ticks, as well as to determine their prevalence in various regions of Lithuania and Latvia. The prevalence of Rickettsia spp. in geographically distinct populations of D. reticulatus on transect Baltic-Adriatic regions was compared. The molecular analyses of 1859 D. reticulatus and 361 I. ricinus from 48 localities in Lithuania and Latvia revealed the presence of Rickettsia raoultii in D. reticulatus and Rickettsia helvetica in I. ricinus. The prevalence of pathogens in D. reticulatus (4.9%) and I. ricinus (17%) ranged in different locations from 0% to 36.9% and 0%-31.3%, respectively. Higher overall infection rates were detected in D. reticulatus collected in Poland (15.8%) and Slovakia (11.4%), with the prevalence range in different locations from 0% to 59.6%. Our study is the first demonstration of the presence of R. raoultii in D. reticulatus ticks in the Baltic countries and R. helvetica in questing I. ricinus ticks in Lithuania.