Pathogen and History
The causative agent belongs to the family Bunyaviridae and is classified in the genus Nairovirus (CCHF antigenic group). It is a vasotropic arbovirus which, unlike many other arboviruses, lacks hemagglutinating activity in most strains. There are 8 distinct genotypes of the pathogen globally, each with a strict geographic distribution.
The disease was first described in 1944 by military physicians in Crimea. The infection heavily affected soldiers and settlers during agricultural work (hay harvesting). As early as 1945, researcher M.P. Chumakov successfully isolated the virus from the blood of patients and from ixodid ticks. Two decades later, in 1966, an agent isolated in the Congo was found upon thorough study to be biologically identical to the Crimean virus. This discovery gave the infection its current double name.
Epidemiology and Virus Ecology
Natural foci of the infection are traditionally recorded in southern regions. The reservoir and source of the pathogen are pasture ticks, primarily species of the genus Hyalomma, which can retain the viral particle for up to 250 days. In nature, the virus survives the interepidemic period through unique mechanisms of transmission within the arthropod population:
- Transovarial transmission: the virus is passed from an infected female directly to her offspring.
- Transtadial (transphasic) transmission: the pathogen persists in the organism through its metamorphosis (from larva to nymph and adult).
Vertebrate animals also play a significant role in maintaining natural foci. Larvae and nymphs feed on ground-dwelling birds, hares, and mouse-like rodents. Adult ticks prefer large and small ruminants (cows, sheep) and camels. Infected animals develop viremia lasting up to 10 days—sufficient time to successfully infect new batches of ticks, while the disease itself is largely asymptomatic in animals.
Humans represent a "dead-end host" in this epidemiological chain. The primary route of transmission in natural foci remains vector-borne (bite of an infected tick). However, the contact route of transmission is extremely dangerous; it occurs via skin microtraumas and mucous membranes when handling blood from patients, crushing ticks, or during medical procedures (nosocomial iatrogenic transmission). Less commonly, the airborne (aerosol) mechanism occurs, typically associated with laboratory accidents. Contact transmission has a critical feature—the "ping-pong" effect: upon passage through the human body, the virus sharply increases its virulence, causing these cases to be significantly more severe.
Pathogenesis and Clinical Presentation
The disease can occur in two forms: with hemorrhagic manifestations and without them (the latter is tolerated much better by patients). In the classic hemorrhagic form, the incubation period ranges from 1 to 14 days.
Pathogenesis develops in stages:
- Primary replication: the virus actively multiplies in cells of the macrophage system.
- Hematogenous dissemination: massive release of the pathogen into the bloodstream.
- Vascular damage: due to the strict vasotropism of the virus, severe generalized capillarotoxicosis develops.
In the complete blood count, against the background of the classic triad (fever, intoxication, hemorrhagic syndrome), thrombocytopenia and leukopenia are clearly evident. Mortality in the hemorrhagic form reaches 16–20%, and up to 50% with contact transmission. The main causes of patient death are toxic shock syndrome (TSS), massive uncontrollable hemorrhages, and acute hepatorenal failure.
The convalescence period is extremely prolonged. A patient's working capacity is restored no earlier than one to two months later, and profound functional impairments may persist for 1–2 years. Recovery leads to strong immunity: complement-fixing and precipitating antibodies circulate in the blood for more than 5 years.
Diagnosis, Treatment, and Biosafety
Several modern approaches are used for microbiological diagnosis:
- Rapid diagnostics: testing of blood, vectors, or autopsy material using indirect hemagglutination assays (IHA) and immunofluorescence assays (IFA) with monoclonal sera.
- Molecular biology methods: PCR to detect specific viral RNA and ELISA to detect pathogen antigens.
- Virological method: isolation of the virus from blood or internal organs of deceased individuals by inoculating newborn white mice or cell cultures, followed by identification via IFA.
- Serology: screening for specific antibodies in paired sera using ELISA.
Etiotropic therapy is based on antiviral drugs (Ribavirin, Reaferon). Early immunotherapy is critically important and effective only within the first 3 days of illness: heterogeneous specific equine immunoglobulin, immune serum, plasma, or specific immunoglobulin derived from convalescents or vaccinated individuals is administered.
Patients with suspected infection require immediate hospitalization strictly in isolated rooms (boxes). The reason for this isolation lies in the extremely high concentration of the virus in the blood, creating a massive risk of nosocomial spread. Only specially trained personnel are allowed to work with these patients. For risk groups (e.g., laboratory personnel), specific prophylaxis is available using a formalin-inactivated vaccine prepared from the brain tissue of infected newborn rats or mice.