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Lyme borreliosis is the most prevalent tick-borne disease in Europe. It is caused by spirochaetes of the Borrelia burgdorferisensu lato (s.l.) complex and transmitted to humans by ticks of the genus Ixodes. Borrelia afzelii, Borrelia garinii, and Borrelia valaisianaare the most common genospecies in Central Europe. In contrast, Borrelia lusitaniaepredominates in Mediterranean countries such as Portugal, Morocco, and Tunisia. In Slovakia, its prevalence is low and restricted to only a few sites.

A total of 1810 Ixodes ricinusticks was collected from the vegetation from 2 different habitat types: urban and natural. Urban habitats were represented by cemeteries and public parks in the following towns: Bratislava, Malacky, and Martin at 150m and 400m above sea level. Natural habitats were selected in the mountain forest of the Martinské hole Mts. in Central Slovakia at 3 different altitudinal levels, i.e. 600m, 800m and 1000ma.s.l. All ticks were tested for the presence of spotted fever group rickettsiae. The DNA of Rickettsiaspp. was identified in 9% of all tested ticks. Rickettsia-infected ticks were present in both, urban and sylvatic sites at all studied altitudes. Four different species of Rickettsiawere present in positive I. ricinusticks. Rickettsia helveticawas identified in 77 out of 87 Rickettsia-positive I. ricinusticks, followed by 8 samples that belonged to Rickettsia monacensisand 2 of the positive ticks were infected with different unidentified Rickettsiaspp. Due to the association of R. helveticaand R. monacensiswith human infections, it is essential to understand which species of Rickettsiacirculate in the natural foci of Slovakia. Circulation of pathogenic rickettsiae in urban as well as natural habitats at different altitudinal levels in Slovakia emphasizes that infection risk is very common throughout this Central European country.

Spirochetes belonging to the Borrelia burgdorferi sensu lato (s. l.) complex have evolved remarkable ability to survive in diverse ecological niches during transmission cycles between ticks and vertebrate hosts by variable gene expression. To understand the events during spirochete transmission from feeding ticks to hosts, mRNA levels of selected B. afzelii genes (bbk32, dbpA, ospA, ospC and vlsE) were measured by quantitative real-time SYBR Green PCR. B. afzelii infected Ixodes ricinus nymphs fed on laboratory BALB/c mice for 0, 24, 48, and 72 hours. The mRNA levels of the constantly expressed flagellin gene were used for the relative quantification of selected genes. Differences in gene expression profiles were observed in unfed ticks and during tick feeding. mRNA levels of bbk32 and dbpA showed distinctive decreasing patterns during the first 24 hours post-attachment, while ospC and vlsE mRNA levels increased significantly during the feeding process. In contrast, ospA levels decreased for the 48 hours of tick feeding and slightly increased by 72 hours. More detailed and comprehensive studies on regulation of gene expression in different Borellia genospecies on the vector–host interface would aid to develop effective strategies in preventing pathogen transmission.