Overview of Crimean-Congo Hemorrhagic Fever

The etiologic agent, CCHF virus (genus Nairovirus, family Bunyaviridae), is an enveloped negative-sense, trisegmented, single-stranded RNA virus. The virus has been reported in a wide area from South Africa through southern Europe, Eurasia, and into 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 significant genetic diversity somewhat correlated with geographic origin of the virus. However, anomalies to this pattern suggest that dispersal of host ticks by migratory wildlife such as birds or the movement of livestock (by people) may act to perturb the “normal” geographic distribution of CCHF virus subpopulations.

The virus replicates in the host tick as it passes from larval through adult stages (transstadial 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, while most Hyalomma spp ticks are multihost and use larger vertebrates as the host for the adult stage of their life cycle.

In experimental inoculations, sheep and cattle become infected but develop only transient and mild increases of body temperature with little evidence of clinical disease. 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, but 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, while other tests, such as complement fixation and indirect fluorescent antibody, can detect antibodies for shorter periods after infection. Antibody prevalence in adult livestock species in endemic regions can be >50%.

The antiviral drug ribavirin has been used in treatment of human disease in South Africa, although placebo-controlled trials have not been completed. Lack of significant clinical disease in livestock warrants no treatment considerations.

Control strategies for human infection 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.