Diagnostics of tick-borne rickettsioses in Germany: A modern concept for a neglected disease

Tick-borne rickettsioses in humans occur worldwide and are caused by obligate intracellular bacteria belonging to the spotted-fever group (SFG) within the genus Rickettsia (R.). These tick-borne rickettsioses are among the most underdiagnosed vector-borne diseases in Germany: Due to the variety of unspecific clinical signs, they are not easily recognised. The clinical picture ranges from subclinical to fatal courses, but may be difficult to differentiate from other febrile conditions without specific tests. Even to date, diagnosis is either based on clinical findings, a record of tick exposure, or indirect serological detection of the pathogens. Herein, we briefly discuss modern diagnostic tools for important tick-borne rickettsial infections with emphasis on new molecular diagnostic assays. As one example, we present a novel real-time polymerase chain reaction (PCR) protocol that facilitates genus-specific, rapid, and sensitive detection of rickettsial pathogens. A conserved region of the rickettsial citrate synthase gene (gltA) is amplified and detected by a 5′-nuclease probe in a LightCycler instrument. Sensitivity was consistently high at less than 23 genome copies per reaction. This detection system has been evaluated both as a useful tool in epidemiological investigations in ticks and in human diagnostics. We describe a rational diagnostic approach for the detection of tick-borne human rickettsioses which consists of that real-time PCR, isolation of rickettsiae in cell culture, multi-locus sequence typing, and serology. Its implementation recently led to the first isolation and characterisation of R. africae in Germany from a patient returning from Zimbabwe. In conclusion, tick-borne rickettsioses should be considered in patients presenting with fever, headache, and rash following a tick bite. Further studies are needed to determine the epidemiology and clinical importance of these pathogens in Germany.