Country-wide seroprevalence studies on Crimean-Congo hemorrhagic fever and hantavirus infections in general population of Bulgaria.

Crimean-Congo hemorrhagic fever (CCHF) and hantavirus infections are the two viral hemorrhagic fevers spread in Europe. To test actual circulation of CCHF virus (CCHFV) and hantaviruses in Bulgaria, we conducted country-wide seroepidemiological studies. Serum samples were collected prospectively from 1500 residents of all 28 districts in Bulgaria. CCHFV seroprevalence of 3.7% was revealed. Anamnesis for tick bites, contact with livestock, age over 40 years and residency in Haskovo district were found as risk factors. The highest CCHFV seroprevalence was observed in the known endemic districts in southeastern Bulgaria: Haskovo (28%) and Yambol (12%). Reactive samples were found in residents of 20 of the 28 districts in Bulgaria. In comparison with the previous studies, the data presented indicate that CCHFV increased substantially its circulation in the endemic regions and was introduced in many new areas. Hantavirus seroprevalence was based on results of the immunoblot and estimated as 3.1%. Surprisingly, contrary to all available data, Puumala virus seroprevalence rate was 2.3% versus 0.8% of Dobrava-Belgrade virus. Evidence for hantavirus IgG seropositivity was found in residents of 23 of the 28 districts in the country. The first hantavirus seroprevalence study in Bulgaria showed that Puumala virus is probably more wide-spread in the country than Dobrava-Belgrade virus.