Tick Research Group

Research Group on Ticks and Tick-Borne Microorganisms

Rickettsia spp.

The genus Rickettsia comprises a group of small, specialised, obligate intracellular bacteria that can only replicate inside the cells of their host. Certain members of this genus belong to the Spotted Fever Group (SFG) and are emerging pathogens responsible for tick-borne rickettsioses [1]. While Mediterranean spotted fever (caused by Rickettsia conorii) is a well-known risk along Southern European coastlines, Central Europe features a distinct array of rickettsial species and clinical manifestations [1, 2].

Rickettsia raoultii. The arrow indicates intracellular bacteria. ©Michiel Wijnveld

The Central European Spotted Fever Group

Rather than causing a generalized rash across the whole body, the most common Rickettsia species native to Central Europe typically result in localised, tissue-specific syndromes [1, 3]:

  • Rickettsia slovaca & Rickettsia raoultii: These two species are the primary causes of a condition known as SENLAT (Scalp Eschar and Neck Lymphadenopathy After Tick Bite), also traditionally referred to as TIBOLA (Tick-Borne Lymphadenopathy) [1, 3]. Patients typically develop a characteristic dark, crusted ulcer (an eschar) at the bite site on the scalp, accompanied by painfully swollen lymph nodes in the neck.
  • Rickettsia helvetica & Rickettsia monacensis: These species are widely distributed across Central European forests. Infections generally present as a mild-to-moderate flu-like illness characterised by sudden fever, persistent headaches, and myalgia (muscle pain) [2, 4].

Dual Vectors and High Central European Prevalence

The landscape of rickettsial risk in Central Europe is driven by two distinct hard tick vectors, each maintaining its own set of bacterial strains:

  • The Castor Bean Tick (Ixodes ricinus): This widespread, generalist tick is the primary vector for R. helvetica and R. monacensis. Urban surveillance data highlight its steady presence. For instance, a multi-year study in popular Viennese recreational areas detected Rickettsia DNA in 13.8% of questing I. ricinus ticks in 2019 and 4.6% in 2020 [4].
  • The Ornate Dog Tick / Meadow Tick (Dermacentor reticulatus): This species prefers grasslands, river basins, and floodplains, serving as the primary vector for R. raoultii and R. slovaca [3]. Rickettsia prevalence tends to be exceptionally high in this vector. A multi-regional survey across the Czech Republic, Slovakia, and Hungary revealed an overall Rickettsia infection rate of 47.9% among collected D. reticulatus ticks [3]. Notably, field research in Austria successfully isolated and propagated a novel, viable strain of R. raoultii directly from D. reticulatus populations within the Donau-Auen (Lobau) National Park, proving that these vectors maintain active reservoirs of the bacteria in Central European wetlands [5].

Because rickettsial infections frequently present with non-specific or highly localized symptoms like scalp lesions, they are easily misdiagnosed as simple skin infections. As climate shifts expand the seasonal activity of both Ixodes and Dermacentor ticks, understanding these specific regional pathogens is becoming vital for Central European public health [1, 2].

References & Academic Citations

  1. Parola P., Paddock, C. D., Socolovschi, C., Labruna, M. B., Mediannikov O., Kernif, T., Abdad, M. Y.,, Stenos J., Bitam I., Fournier P.-E., Raoult D. (2013). Update on tick-borne rickettsioses around the world: a geographic approach. Clinical Microbiology Reviews, 26(3), 657-702. https://doi.org/10.1128/CMR.00032-13
  2. Kiesow, M., Schreiber, C., Kampen, H., & Walther, D. (2023). Spotted Fever Group Rickettsiae in Ticks and Small Mammals from Grassland and Forest Habitats in Central Germany. Pathogens, 12(7), 933. https://doi.org/10.3390/pathogens12070933
  3. Balážová, A., Földvári, G., Bilbija, B., Nosková, E., & Široký, P. (2022). High Prevalence and Low Diversity of Rickettsia in Dermacentor reticulatus Ticks, Central Europe. Emerging Infectious Diseases, 28(4), 893-895. https://doi.org/10.3201/eid2804.211267
  4. Schötta, A. M., Stelzer, T., Stanek, G., Stockinger, H., & Wijnveld, M. (2022). Bacteria and protozoa with pathogenic potential in Ixodes ricinus ticks in Viennese recreational areas. Wiener klinische Wochenschrift, 135(7-8), 177-184. https://doi.org/10.1007/s00508-022-02046-7
  5. Wijnveld, M., Schötta, A. M., Pintér, A., Stockinger, H., & Stanek, G. (2016). Novel Rickettsia raoultii strain isolated and propagated from Austrian Dermacentor reticulatus ticks. Parasites & Vectors, 9(1), 567. https://doi.org/10.1186/s13071-016-1858-x