Crimean-congo Hemorrhagic Fever: Introduction

Etiology and Epidemiology

Transmission and Pathogenesis

Clinical Findings and Diagnosis

Treatment

Control and Prevention

Crimean-Congo hemorrhagic fever (CCHF) is a severe hemorrhagic viral disease of humans acquired from infected ticks, tissues of infected wild or domestic animals, and from human patients with the disease.

Etiology and Epidemiology:

The etiologic agent, CCHF virus (genus Nairovirus, family Bunyaviridae) is an enveloped negative-sense, 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 humans may act to perturb the “normal” geographic distribution of CCHF virus subpopulations.

Transmission and Pathogenesis:

The virus replicates in the host tick as it passes from larval through adult stages (trans-stadial transmission) and 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. Vertebrates ranging from 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.

Clinical Findings and Diagnosis:

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. 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%.

Treatment:

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 and Prevention:

Control strategies for human infection include the avoidance of tick bites through use of repellents and appropriate protection when slaughtering or grooming animals. Medical personnel should use appropriate barrier nursing techniques and universal precautions when handling suspect patients.