Abstract
BackgroundSpotted Fever Group (SFG) Rickettsiae can cause febrile diseases with or without rash in humans worldwide. In Germany only limited data are available about their medical significance. Serological screening tests for antibodies against rickettsiae usually only distinguish between SFG and Typhus Group (TG) Rickettsiae due to the strong cross reactivities within the groups. Seroprevalence rates in dogs, as possible sentinels for tick-borne diseases, could serve as an indicator for the distribution of different Rickettsia species.MethodsIn this study, a micro-immunofluorescence assay (micro-IFA) was established for detection and differentiation of antibodies against five Rickettsia species in dogs (R. helvetica, R. raoultii, R. slovaca, R. monacensis and R. felis). Dogs that never left Germany (n = 605) previously investigated with an SFG-ELISA were included in this study and screened at a 1:128 dilution. Endpoint titres of fifty randomly selected seropositive samples of each of the five investigated regions in Germany were determined in order to allow a differentiation of the causative Rickettsia species. Sensitivity and specificity of the micro-IFA were compared with ELISA results of the previous study.ResultsA total of 93.9% of the dogs were positive for antibodies of the SFG Rickettsiae at the screening titer of 1:128. Differentiation of SFG Rickettsiae with the micro-IFA was possible in 70.4%, but in 29.6% of the cases the detected antibodies were not differentiable. Considering a clear differentiation by a twofold titre difference between observed reactions, the seroprevalence rates were 66.0% for R. helvetica, 2.8% for R. raoultii, 1.6% for R. slovaca, but no serological reaction could be clearly attributed to R. monacensis or R. felis. No statistically significant regional differences were found for R. helvetica, R. slovaca and R. raoultii comparing the five regions of Germany. Comparison of micro-IFA with ELISA revealed a sensitivity of 82.0% and a specificity of 83.8% for the Rickettsia SFG ELISA.ConclusionsThe micro-IFA is a useful serological tool to differentiate antibodies against different Rickettsia species in dogs. Seroprevalence rates in dogs correspond to the prevalence rates and distribution of Rickettsia-carrying tick species.
Highlights
Spotted Fever Group (SFG) Rickettsiae can cause febrile diseases with or without rash in humans worldwide
The heterogeneous SFG contains >20 Rickettsiae, mainly transmitted by ticks, except for R. felis which is transmitted by fleas and R. akari which is transmitted by mites [2,3,4]
Recent genomic analyses indicate the divison into four groups: the Typhus Group (TG), the SFG, the ancestral group (AG) and the transitional group (TRG), which includes R. felis [5]
Summary
Spotted Fever Group (SFG) Rickettsiae can cause febrile diseases with or without rash in humans worldwide. Rickettsiae are short rod-shaped gram-negative, obligate intracellular bacteria [1] They are, regarding the clinical and serological perspective, divided into two major groups: the Typhus Group (TG) and the Spotted Fever Group (SFG). Various molecular and serological methods have been described for the detection and differentiation of Rickettsia species. Brouqui et al [12] described a micro-immunofluorescence method which allows the investigation of up to nine different rickettsial antigens in one spot as a suitable method to differentiate the causative Rickettsia species by determination of endpoint titres. In Germany, six species of the SFG Rickettsiae have been detected in ticks by molecular methods (Table 1). R. helvetica is generally associated with uneruptive fever, but cases with more severe
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