Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne viral disease of humans and endemic in more than 30 countries. It circulates between ixodid (particularly Hyalomma) ticks and amplifying vertebrate hosts; infection in animals is typically subclinical, whereas human cases can be severe, with case fatality rates approaching 40%. Diagnosis in animals is conducted primarily for surveillance purposes, and control efforts focus on tick management, because of the absence of approved vaccines or specific treatments. CCHF is a notifiable disease in many countries, including the US; suspected or confirmed cases should be reported in accordance with national or local animal and/or public health authorities.
Crimean-Congo hemorrhagic fever (CCHF) is a severe hemorrhagic disease affecting humans caused by the zoonotic CCHF virus. Many animal species and some birds can be infected without clinical signs of illness in natural infection. Ticks are the main vector for human disease, as well as contact with blood or tissues of infected wild or domestic animals or that of other infected human patients.
CCHF was first described in 1944, during an outbreak of hemorrhagic febrile illness in the Crimean Peninsula, and again in 1956, in the Democratic Republic of the Congo (formerly Zaire). Although these outbreaks were initially considered unrelated, the virus was isolated and characterized in 1967, and by 1969, both epidemics were confirmed to have been caused by the same pathogen. The disease was subsequently renamed Crimean-Congo hemorrhagic fever to reflect its identification in both regions (1, 2).
Historically, CCHF has been known by many names, including Crimean fever, Congo fever, Central Asian hemorrhagic fever, Uzbekistan hemorrhagic fever, Hungribta (blood taking), Khunymuny (nose bleeding), and Karakhalak (black death) (3).
Etiology of Crimean-Congo Hemorrhagic Fever
The causative agent of Crimean-Congo hemorrhagic fever (CCHF) is the CCHF virus, an enveloped, negative-sense, single-stranded RNA virus with a trisegmented genome, classified within the genus Orthonairovirus, family Nairoviridae, and order Bunyavirales (1, 4, 5, 6, 7).
The CCHF virus is principally associated with ticks of the genus Hyalomma; however, it has also been isolated from other genera of ixodid ticks.
The CCHF virus exhibits considerable genetic diversity, driven by frequent reassortment of its genomic segments. Its tripartite genome comprises small (S), medium (M), and large (L) segments, which encode the viral capsid, envelope glycoproteins, and RNA polymerase, respectively (4). On the basis of S-segment variability, six to seven genotypes have been identified, and they generally circulate in defined geographic regions (5, 8, 9). These circulation patterns can often provide valuable insight for molecular epidemiological research, yet they introduce complexity for diagnostic accuracy and the development of medical countermeasures. The extent to which genotype variation influences disease severity remains unclear.
Pathogenesis of Crimean-Congo Hemorrhagic Fever
The pathogenesis and immunobiology of CCHF are not yet fully understood. However, it is well recognized that the disease course in animals is limited (10).
After inoculation via a tick bite, CCHF virus undergoes initial viral replication in local tissues and regional lymph nodes followed by a transient systemic dissemination (ie, viremia). On the basis of the clinical progression in humans, it is reasonable to assume that animals experience no endothelial injury, cytokine dysregulation, or coagulopathy, which explains the absence of clinical signs.
The CCHF virus is cleared by innate and humoral immune responses, leading to seroconversion without clinical signs in most species. Consequently, animals function primarily as amplifying hosts rather than clinically affected patients. Pathogenesis in animals is of greatest relevance at the population level, as it supports maintenance of the virus in enzootic cycles and subsequent spillover risk to humans.
Pearls & Pitfalls
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Epidemiology of Crimean-Congo Hemorrhagic Fever
CCHF is the most geographically extensive of the hemorrhagic fevers, with circulation reported across much of Asia, Africa, the Middle East, and southeastern Europe (11, 12) (see ).
Countries and areas considered endemic for CCHF are visible in red.
Courtesy of US Centers for Disease Control and Prevention (CDC) About Crimean-Congo Hemorrhagic Fever. 2025. Accessed April 9, 2026. https://www.cdc.gov/crimean-congo-hemorrhagic/about/index.html.
CCHF has been detected in countries previously unaffected, like Spain, Jordan, and France (12, 13, 14); additionally, studies have shown the global distribution of Hyalomma ticks is expanding as ecological and climatic factors change, particularly across Europe (13, 14, 15, 16, 17) (see ).
Areas in red indicate Hyalomma spp tick distribution.
Courtesy of Bonnet SI, Vourc’h G, Raffetin A, et al. The control of Hyalomma ticks, vectors of the Crimean–Congo hemorrhagic fever virus: Where are we now and where are we going?PLoS Negl Trop Dis.2022; 16(11): e0010846. https://doi.org/10.1371/journal.pntd.0010846.
Movement of birds, livestock, and humans can all contribute to disease spread.
Human populations at increased risk for exposure to CCHF include those working in close contact with livestock (eg, farmers, veterinarians, para-veterinary professionals, slaughterhouse workers) and anyone participating in outdoor recreational activities, such as hunting, camping, or hiking, in areas where CCHF is present.
Transmission of Crimean-Congo Hemorrhagic Fever
Transmission of Crimean-Congo hemorrhagic fever in animals occurs primarily through tick bites, whereas transmission to humans can result from tick bites or from contact with blood or tissues from infected ticks, animals, or humans (1, 2, 5).
Hard ticks (Ixodidae family) are the vectors and reservoirs of CCHF virus. Hyalomma ticks are primarily associated with this disease; however, Rhipicephalus and Dermacentor genera can also be competent vectors (2, 16).
Within tick populations, viral transmission can occur through several mechanisms (16):
transstadial, in which the virus persists across larval, nymph, and adult life stages
vertical, whereby infected females pass the virus to their offspring
venereal, between ticks during mating
nonviremic via cofeeding, in which uninfected ticks acquire the virus while feeding in proximity to infected ticks on the same host
Ticks, once infected with CCHF, remain so for life, thereby maintaining viral circulation through an enzootic tick-vertebrate-tick cycle.
Ticks of the Hyalomma genus will infest a wide range of wildlife, including hares, deer, antelope, ostrich, and domestic livestock, such as cattle and small ruminants (1, 5). Unlike other genera, Hyalomma ticks are considered "hunter" ticks rather than ambushers, actively pursuing their hosts (see ).
An adult female Hyalomma tick. Characteristic features include elongated mouthparts (palps longer than they are wide); a simple dark, pitted scutum covering the anterior portion of the dorsum (the scutum covers the entire dorsal surface in males); and the distinctly banded or striped legs. In contrast to many ixodid ticks, Hyalomma ticks have true eyes, located laterally on either side of the scutum, which may support vision-guided host-seeking behavior.
Courtesy of Acarologiste, CC BY-SA 4.0 [https://creativecommons.org/licenses/by-sa/4.0], via Wikimedia Commons.
Birds are generally believed to be resistant to infection with CCHF, with ostriches a notable exception. Importantly, even though uninfected, many bird species are frequently infested with Hyalomma ticks. Immature ticks can remain attached for 2–3 weeks, so birds potentially play a role in the long-distance passive dispersal of infected ticks into new areas (5, 16, 18).
Similarly, movement and trade of livestock can contribute to the introduction of ticks into new regions, furthering geographical spread of the CCHF virus. (16, 18).
Zoonotic Relevance of Crimean-Congo Hemorrhagic Fever
Crimean-Congo hemorrhagic fever is a notifiable disease in many countries, including the US; suspected or confirmed cases should be reported promptly in accordance with applicable national and local animal health reporting requirements, and, because of its zoonotic risk, to appropriate public health authorities.
Clinical Findings of Crimean-Congo Hemorrhagic Fever
Subclinical to mild, nonspecific signs in animals
Animals naturally infected with Crimean-Congo hemorrhagic fever do not show overt clinical signs, unlike humans, who can exhibit severe, multisystemic disease. However, infected animals without clinical signs still experience viremia at levels sufficient to transmit virus to uninfected ticks (19), with the transmission period lasting between 2 and 15 days (2, 20). They also develop a humoral immune response (13, 20).
Some mild, nonspecific clinical signs of CCHF have been demonstrated in animals in experimental settings (eg, transient low-grade fever, lethargy, and decreased appetite) (5).
Hemorrhagic disease in humans is the most common clinical sign of concern in CCHF.
Diagnosis of Crimean-Congo Hemorrhagic Fever
Molecular-based diagnostic assays (eg, PCR assay and reverse transcription PCR assay)
Serological testing, principally ELISA
Diagnosis of active or recent Crimean-Congo hemorrhagic fever virus infection in animals is not common, and any testing is generally performed for surveillance purposes.
In general, CCHF virus can be detected via various molecular assay combinations (including conventional, quantitative, and nested techniques of reverse transcription PCR [RT-PCR] assays, with RT-qPCR typically preferred for its higher sensitivity, specificity, and faster time to results), virus isolation, and serological techniques such as ELISA for IgM or IgG antibodies and indirect immunofluorescence (1, 2, 5, 19).
In humans, a combination of molecular and serological methods of diagnosing CCHF virus infection is the preferred approach, and in cases with complex serological results, next-generation sequencing has been used to confirm pathogen identification (2). Note that PCR assay primers will be dependent on the viral genotype, which is tied to geographical circulation.
Treatment, Control, and Prevention of Crimean-Congo Hemorrhagic Fever
No treatment in animals
No vaccines available in animals
Tick control measures
Treatment of Crimean-Congo hemorrhagic fever in animals is not needed because of the absence of clinical evidence of disease. No vaccines are available for animals.
Clinical management of human cases of CCHF is primarily supportive. Antiviral drugs like ribavarin and favipiravir have been used with varying degrees of success (21).
Research is ongoing into novel drugs and vaccines for use against CCHF, some of which have shown promising results (21, 22, 23). Notably, the discovery of an entry receptor for CCHF virus might represent a useful pharmacological target (24).
Control and prevention strategies for CCHF emphasize vector management. The use of acaricides in animals or repellents for people, such as DEET and appropriate light-colored clothing, can help minimize the risk of tick bites. Ticks found attached should be removed immediately.
Those working with or otherwise in proximity to livestock and wildlife (eg, agricultural or slaughterhouse workers, hunters) should employ personal protective equipment to protect against any splashing of blood or contact with tissue(s) of infected animals.
Medical personnel should use appropriate barrier nursing techniques and standard precautions when handling suspect CCHF patients.
Key Points
CCHF is a viral, tick-borne disease transmitted principally by Hyalomma spp ticks.
The range of CCHF distribution is determined by the presence of the tick vector.
The CCHF virus is maintained by a transmission cycle between the tick vector and small animals (such as hares and ground-dwelling birds) and production animals.
For More Information
About Crimean-Congo Hemorrhagic Fever (CCHF). CDC Viral Hemorrhagic Fevers. Accessed April 9, 2026.
Crimean-Congo haemorrhagic fever.WHO Health Topics. Accessed April 9, 2026.
Sorvillo TE, Rodriguez SE, Hudson P, et al. Towards a Sustainable One Health Approach to Crimean-Congo Hemorrhagic Fever Prevention: Focus Areas and Gaps in Knowledge. Trop Med Infect Dis 2020:5(3).
Crimean-Congo Hemorrhagic Fever. Iowa State Fact Sheet.
World Organization for Animal Health (WOAH). Chapter 3.1.5 – Crimean-Congo Haemorrhagic Fever. Terrestrial Animal Health Manual. 2024.
World Health Organization. Prioritizing diseases for research and development in emergency contexts. Accessed April 9, 2026. https://www.who.int/activities/prioritizing-diseases-for-research-and-development-in-emergency-contexts
World Health Organization. WHO Pathogens Prioritization: A Scientific Framework for Epidemic and Pandemic Research Preparedness. Accessed April 9, 2026. https://cdn.who.int/media/docs/default-source/consultation-rdb/prioritization-pathogens-v6final.pdf?sfvrsn=c98effa7_9&download=true
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