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Molecular and Clinical Characterization of Crimean-Congo Hemorrhagic Fever in Bulgaria, 2015-2024
Kim Ngoc1, Ivan Stoikov1, Ivelina Trifonova2
1Department of Microbiology, National Center of Infectious and Parasitic Diseases, 1504 Sofia, Bulgaria.
Insights
Crimean-Congo hemorrhagic fever (CCHF) is endemic in Bulgaria, with 24 cases reported between 2015-2024. Phylogenetic analysis reveals a persistent, genetically stable CCHF virus lineage in the region, emphasizing the need for ongoing surveillance.
Area of Science:
- Virology
- Epidemiology
- Public Health
Background:
- Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne zoonotic viral disease.
- Bulgaria is a European country with consistent annual reporting of human CCHF cases.
- Understanding CCHF epidemiology and viral genetics in endemic regions is crucial for public health.
Purpose of the Study:
- To describe the clinical and epidemiological features of CCHF cases in Bulgaria from 2015 to 2024.
- To analyze the genetic characteristics and phylogenetic relationships of CCHF virus (CCHFV) strains circulating in Bulgaria.
- To assess the long-term persistence of CCHFV lineages in the region.
Main Methods:
- Descriptive epidemiological analysis of 24 confirmed CCHF cases.
- Laboratory confirmation using enzyme-linked immunosorbent assay (ELISA) and real-time reverse transcriptase polymerase chain reaction (RT-qPCR).
- Whole-genome sequencing and phylogenetic analysis of two CCHFV strains.
Main Results:
- Common clinical manifestations included fever, fatigue, gastrointestinal symptoms, thrombocytopenia, leukopenia, liver dysfunction, and coagulopathy.
- Two fatal cases were recorded during the study period.
- Phylogenetic analysis placed Bulgarian strains within the Europe 1 genotype, closely related to Turkish and neighboring country strains, indicating a stable viral lineage.
Conclusions:
- The study highlights the continued circulation of a genetically stable CCHF virus lineage in Bulgaria.
- Consistent clinical and molecular surveillance is essential for monitoring CCHFV evolution and its public health impact.
- Findings underscore the importance of regional collaboration in CCHF control efforts.
Abstract:
Crimean-Congo hemorrhagic fever (CCHF) is a zoonotic viral disease endemic to parts of Africa, Asia and southeastern Europe. Bulgaria is one of the few European countries with the consistent annual reporting of human CCHF cases. This study provides a descriptive overview of 24 confirmed CCHF cases in Bulgaria between 2015 and 2024. Laboratory confirmation was performed by an enzyme-linked immunosorbent assay (ELISA) and/or real-time reverse transcriptase polymerase chain reaction (RT-qPCR) testing. Common findings included fever, fatigue, gastrointestinal symptoms, thrombocytopenia, leukopenia, liver dysfunction and coagulopathy. Two fatal cases were recorded. Two samples collected in 2016 and 2024 were subjected to whole-genome sequencing. Phylogenetic analysis showed that both strains clustered within the Turkish branch of the Europe 1 genotype and shared high genetic similarity with previous Bulgarian strains, as well as strains from neighboring countries. These findings suggest the long-term persistence of a genetically stable viral lineage in the region. Continuous molecular and clinical surveillance is necessary to monitor the evolution and public health impact of CCHFV in endemic areas.
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