Hemorrhagic fever with renal syndrome and Crimean-Congo hemorrhagic fever as causes of acute undifferentiated febrile illness in Bulgaria.

Hemorrhagic fever with renal syndrome (HFRS) and Crimean-Congo hemorrhagic fever (CCHF) are the 2 widespread viral hemorrhagic fevers occurring in Europe. HFRS is distributed throughout Europe, and CCHF has been reported mainly on the Balkan Peninsula and Russia. Both hemorrhagic fevers are endemic in Bulgaria. We investigated to what extent acute undifferentiated febrile illness in Bulgaria could be due to hantaviruses or to CCHF virus. Using enzyme-linked immunosorbent assays (ELISAs), we tested serum samples from 527 patients with acute febrile illness for antibodies against hantaviruses and CCHF virus. Immunoglobulin M (IgM) antibodies against hantaviruses were detected in 15 (2.8%) of the patients. Of the 15 hantavirus-positive patients, 8 (1.5%) were positive for Dobrava virus (DOBV), 5 (0.9%) were positive for Puumala virus (PUUV), and the remaining 2 were positive for both hantaviruses. A plaque reduction neutralization test (PRNT) confirmed 4 of the 10 DOBV-positive samples. PRNT was negative for all PUUV-positive samples. Serologic evidence of recent CCHF virus infection was found in 13 (2.5%) of the patients. Interestingly, HFRS and CCHF were not only detected in well-known endemic areas of Bulgaria but also in nonendemic regions. Our results suggested that in endemic countries, CCHF and/or HFRS might appear as a nonspecific febrile illness in a certain proportion of patients. Physicians must be aware of possible viral hemorrhagic fever cases, even if hemorrhages or renal impairment are not manifested.