This study was performed to assess viral load, viral nucleocapsid (N), and glycoprotein precursor (GPC) antibodies in consecutive samples obtained from Crimean-Congo hemorrhagic fever patients to reveal viral replication kinetics and antiviral immune responses during the early stages of the infection. Among 116 samples from 20 individuals, 43.9% and 76.7% were positive for viral RNA and IgM/IgG antibodies, respectively, whereas both markers could be detected in 22.4%. Mean duration of viremia was 3 days (range: 1-6 days). N-IgM antibodies were identified as the initial serological marker during the infection, becoming detectable in a median of 2-3 days after disease onset, followed by GPC-IgM (4-6 days) and IgG antibodies (5-6 days). Clearance of viremia followed or coincided N-IgM response. Partial S gene sequences amplified in viremic patients were identical or closely related to previously characterized strains and grouped within European lineage I group II viruses via neighbor-joining analysis without significant amino acid substitutions. (C) 2014 Elsevier Inc. All rights reserved.