Prevalence of ticks infected withFrancisella tularensis in natural foci of tularemia in western Slovakia

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Abstract
The prevalence of ticks infected withF. tularensis was followed during a systematic surveillance in endemic area of tularemia in western Slovakia over the years 1984–93. Ticks were collected from vegetation in localities of Podunajské Biskupice, in the vicinity of the capital of Slovakia, Bratislava, near the river Danube. In total 6033 ticks, mostly adults ofDermacentor reticulatus andIxodes ricinus (4994 and 1004, respectively) and 35 nymphs ofHaemaphysalis concinna, were examined for the presence ofF. tularensis. Out of 4542 starving ticks, 34F. tularensis strains were isolated predominantly fromD. reticulatus (30), and to a smaller extent also fromI. ricinus (3) andH. concinna (1). Natural infection withF. tularensis was further proved from 1491 adults ofD. reticulatus fed on laboratory animals, rabbits and white mice, together in 27 cases. From that, 21 times it was by positive isolation either from suspensions of partly or fully engorged ticks and their feaces, or from spleens of animals dead after the feeding of ticks. In addition, solely the development of antibodies against the agent was confirmed in 6 rabbit hosts. The presence ofF. tularensis in all the above mentioned tick species and namely the relatively high and permanent infestation ofD. reticulatus adults, ranging between 0.5–2% during the followed time period, demonstrated the maintenance of active natural focus of tularemia in the area under study. The present paper also emphasizes the epidemiologic consequence of various species of ticks in endemic foci of tularemia and the aspect of possible ways of transmission of the agent to humans.