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 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.
Etiology and Epidemiology of Crimean-Congo Hemorrhagic Fever in Animals
The etiologic agent, CCHF virus (genus Orthonairovirus, family Nairoviridae), is an enveloped, negative-sense, trisegmented, single-stranded RNA virus. The virus has been reported in a wide area including South Africa, southern Europe, Eurasia, and parts of western China. The virus is principally associated with ticks of the genus Hyalomma, although it has also been isolated from other genera of ixodid ticks. The global distribution of the virus roughly approximates that of Hyalomma spp ticks. Recent analyses of the genome of the virus suggest that there is appreciable genetic diversity somewhat correlating with geographic origin of the virus. However, anomalies to this pattern suggest that dispersal of host ticks by migratory wildlife such as birds or by the movement of production animals (by people) may alter the expected resultant geographic distribution of CCHF virus subpopulations.
Transmission and Pathogenesis of Crimean-Congo Hemorrhagic Fever in Animals
The CCHF virus replicates in the host tick as it passes from larval through adult stages (trans-stadial transmission), and it can also be transmitted from one generation to the next (transovarial transmission). Thus, the tick not only is a vector but also can be a reservoir of the virus via vertical transmission. Small rodents, lagomorphs, and birds have all been incriminated as sources of infection of immature stages of the tick; whereas most Hyalomma spp ticks are multihost and use larger vertebrates as the host for the adult stage of their life cycle.
Clinical Findings and Diagnosis of Crimean-Congo Hemorrhagic Fever in Animals
Clinical signs have only been demonstrated in experimental settings (e.g., transient fever in calves)
Serologic testing, principally ELISA testing, is intended for surveillance/epizootiology, primarily as a public health tool in determining enzootic areas
In experimental inoculations, sheep and cattle become infected with the CCHF virus, but they develop only transient mild fever. Viremia levels and duration are relatively low and short, and antibodies are detectable shortly after cessation of viremia. Reverse transcriptase-PCR assays can detect the virus; however, primer design should match the viruses found in the region in which human patients, or other materials, have originated. Some tests (principally IgG ELISA) can detect antibodies for the remainder of the life of the animal, whereas other tests, such as complement fixation and indirect fluorescent antibody, can detect antibodies for shorter periods after infection. Antibody prevalence in adult production animals in endemic regions can be >50%.
Treatment of Crimean-Congo Hemorrhagic Fever in Animals
Administration of the antiviral ribavirin
In humans during the acute phase of illness, hemodynamic support through blood replacement and fluid balance management
The antiviral drug ribavirin has been used in the treatment of CCHF in humans in South Africa, although placebo-controlled trials have not been completed. Ribavirin is effective against the virus in vitro; however, clinical trials are not extensive, and the drug is often used in an anecdotal/humanitarian manner. Lack of noteworthy clinical signs of CCHF in production animals warrants no treatment considerations.
Hemorrhagic disease in humans is the most common clinical sign of concern.
Control and Prevention of Crimean-Congo Hemorrhagic Fever in Animals
Control strategies for CCHF infection in humans include the avoidance of tick bites through the use of repellents and appropriate protection when slaughtering or grooming animals. Movement of naive animals into endemic areas provides opportunity for vertebrate amplification of the virus and increasing occupational risk to butchers and hide preparers; tick control when naive animals and endemic stock are mixed is paramount. Medical personnel should use appropriate barrier nursing techniques and universal (standard) precautions when handling suspect 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
Crimean-Congo Hemorrhagic Fever (CCHF). CDC Viral Hemorrhagic Fevers Retrieved 0422, 2021
Crimean-Congo haemorrhagic fever. WHO Health Topics Retrieved 0422, 2021
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.
