The Balkan Peninsula and Bulgaria in particular, is a well-known endemic region for Crimean-Congo hemorrhagic fever (CCHF). This study describes the prevalence of Crimean-Congo hemorrhagic fever virus (CCHFV) among tick populations from areas, previously recognized with emerging cases of CCHF disease in humans. These include regions from the Southeastern (regions of Kardzhali and Haskovo) and Central (region of Stara Zagora) parts of the country. For the period 2006-2010 a total of 911 adult ticks, collected from livestock in endemic areas were studied for presence of CCHFV by an immunofluorescence-hemocytes assay (IFHA) and a reverse transcription-polymerase chain reaction (RT-PCR). The detection rate of CCHFV in the tick population was 2.09%. The prevalence of the virus was determined between 2.01% and 4.83% in the regions of Kardzhali and Haskovo, respectively (Southeastern Bulgaria). In the Central part of the country CCHFV infestation of the ticks was observed in 1.46% (region of Stara Zagora). The results confirmed the mosaic dispersion of CCHFV in the investigated regions. The principal infection vector in the surveyed areas was confirmed to be Hyalomma marginatum marginatum. Rhipicephalus sanguineus and Ixodes ricinus were also detected and may play a role in the transmission of CCHFV. Species distribution of CCHFV-positive ticks was as follows: H. m. marginatum-4.93%; R. sanguineus-2.33%; I. ricinus-1.02%. The combination of IFHA and RT-PCR that are used in this study are useful tools in the algorithm for monitoring endemic areas in Bulgaria.
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