Tick-borne rickettsioses are produced by spotted fever group rickettsiae and cause an expanding spectrum of clinical signs. Until recently, Mediterranean spotted fever caused by Rickettsia conorii was considered the only tick-borne rickettsiosis in Europe (Oteo and Portillo 2012). In the last decade many other species and subspecies of Rickettsia have been discovered and implicated as human pathogens, and new rickettsial syndromes have been described. Lack of (local) awareness among medical health professionals and availability of diagnostic tools (case definitions, serology, PCR etc.) hamper the identification of clinical cases.

The aim of this study was to investigate potential human exposure to rickettsiae by determining their presence in questing ticks collected in an urban park of Budapest (Margaret Island), and a popular hunting and recreational forest area in Hungary (Gemenc). Ticks collected with flagging in 2011–2012 were identified and stored in 70 % ethanol until DNA extraction by alkaline hydrolysis then analyzed with a multiplex qPCR assay as previously described (de Bruin et al. 2015). This included a primer pair specific for R. helvetica gltA gene and another amplifying a different region of gltA of rickettsiae in general (Stenos et al. 2005). Positive samples were analyzed with conventional PCR and sequencing (de Bruin et al. 2015).

We collected 534 Ixodes ricinus from Margaret Island and 162 ticks (34 I. ricinus, 64 Dermacentor reticulatus, 2 D. marginatus and 62 Haemaphysalis concinna) from Gemenc. Rickettsia helvetica was detected in 139 (26 %) out of 534 and 9 (26.5 %) out of 34 questing I. ricinus from the urban park and the rural site, respectively (Table 1). The qPCR specific for Rickettsia spp. was positive in 88 (16.5 %) out of 534 I. ricinus ticks from the urban and 41 (25.3 %) out of 162 ticks from the rural habitat. Prevalence of rickettsiae in I. ricinus did not differ significantly in the two study sites (Table 1). However, both components of infection risk, the hazard (density of infected I. ricinus) and exposure (human presence) is higher in the urban park (Földvári et al. 2014) compared to the rural site. Female I. ricinus ticks in the urban parks were found to have a particularly high prevalence of R. helvetica (44.6 %) suggesting a higher infection risk when humans are bitten by this tick stage. The significantly higher prevalence of R. helvetica and Rickettsia spp. in the adult stages of I. ricinus compared to nymphs from the urban habitat (Fisher’s exact test: p < 0.05) suggests the important role of transstadial infection in the eco-epidemiology of these pathogens (Table 1).

Table 1 Prevalence and diversity of rickettsiae in questing ticks from an urban (Margaret Island) and a rural (Gemenc) habitat in Hungary
Full size table

From the urban habitat 22 R. monacensis and 9 R. helvetica out of 534 questing I. ricinus were identified with the less sensitive conventional PCR and sequencing. Compared to the average ratio of these two rickettsiae in other European studies (Rizzoli et al. 2014; Špitalská et al. 2014), the relatively high prevalence of R. monacensis (originally described from a city park in Germany (Rizzoli et al. 2014)) appears unique probably as a consequence of the eco-epidemiology of the closed island park habitat (Földvári et al. 2014).

Rickettsiae were detected in 57.8 % of D. reticulatus which is much higher compared to the prevalence of 15.5 % reported previously in questing ticks of the same species collected throughout the country (Hornok et al. 2010). We identified R. raoultii infection with sequencing in 31 qPCR-positive D. reticulatus samples from the rural habitat. Tick-borne lymphadenopathy (TIBOLA) patients (Lakos 1997) and R. slovaca and R. raoultii in ticks removed from them have been reported in Hungary (Földvári et al. 2013). Both female (53.7 %) and male (65.2 %) D. reticulatus ticks in the present study had high prevalence of Rickettsia spp. This corroborates with previous findings about the equal role of both tick sexes and both Dermacentor spp. in TIBOLA epidemiology (Földvári et al. 2013).

Our results showed considerable difference between the dominant rickettsial agents in the city park (R. helvetica and R. monacensis) and natural forest habitat (R. raoultii). This is due to the differences of these habitats in their vector diversity. In urban settings, usually I. ricinus dominates (Rizzoli et al. 2014), whereas in natural habitats there is a more diverse tick community even visible in the small rural sample size of the present study (Szekeres et al. 2015). This more diverse tick community extends the range of possible human pathogenic rickettsiae, including newly emerging ones. Both our study sites have frequent human visitors: Margaret Island is a popular recreational and jogging park in the center of Budapest and Gemenc is a popular hunting and hiking area with over 50,000 tourists per year. Since all rickettsiae (R. helvetica, R. monacensis and R. raoultii) detected in this study are proven human pathogens (Fournier et al. 2000; Jado et al. 2007; Jia et al. 2014), we can conclude that despite the distinct eco-epidemiological traits, the risk (hazard and exposure) of acquiring rickettsial infections in both the urban and the rural study sites exists.