Crimean-Congo hemorrhagic fever

Crimean-Congo hemorrhagic fever is an acute zoonotic natural focal viral infection with a transmissible mechanism of transmission, characterized by severe hemorrhagic syndrome and two-wave fever.

Crimean-Congo hemorrhagic fever was first described based on the materials of the outbreak in Crimea (Chumakov M.P., 1944-1947), therefore it was called Crimean hemorrhagic fever (CHF). Later, cases of a similar disease were registered in Congo (1956), where in 1969 a virus similar in antigenic properties to the Crimean hemorrhagic fever virus was isolated. To date, the disease has been registered in European countries, Central Asia and Kazakhstan, Iran, Iraq, the United Arab Emirates, India, Pakistan, and African countries (Zaire, Nigeria, Uganda, Kenya, Senegal, South Africa, etc.).

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Epidemiology of Crimean-Congo hemorrhagic fever

The reservoir and sources of infection are domestic and wild animals (cows, sheep, goats, hares, etc.), as well as more than 20 species of ixodid and argas ticks, primarily pasture ticks of the genus Hyalomma. The main reservoir of infection in nature are small vertebrates, from which livestock is infected through ticks. The contagiousness of animals is determined by the duration of viremia, which lasts about a week. Ticks are a more stable reservoir of infection due to the possibility of sexual and transovarial transmission of the virus. High contagiousness of sick people is noted. In animals and humans, the virus is found in the blood during intestinal, nasal and uterine bleeding, as well as in secretions containing blood (vomit, feces).

Transmission mechanisms are transmissible (by tick bites), as well as contact and airborne. When infected from humans or animals, the main mechanism of transmission is contact transmission due to direct contact with the blood and tissues of infected animals and humans (intravenous infusions, stopping bleeding, performing artificial respiration using the mouth-to-mouth method, taking blood for testing, etc.). The airborne mechanism of infection transmission has been described in cases of intra-laboratory infection of personnel during emergency situations during centrifugation of virus-containing material, as well as in other circumstances if the virus was contained in the air.

The natural susceptibility of people is high. Post-infectious immunity lasts for 1-2 years after the disease.

Main epidemiological features. Crimean-Congo hemorrhagic fever disease is characterized by pronounced natural focality. In countries with a warm climate, foci of infection in the form of outbreaks and sporadic cases are confined mainly to steppe, forest-steppe and semi-desert landscapes. The incidence rate is associated with the period of active attack of adult ticks (in the tropics - all year round). Men aged 20-40 years are most often affected. Cases of infection predominate among individuals of certain professional groups - livestock breeders, agricultural workers, veterinarians and medical workers. Intrahospital outbreaks of infection and intralaboratory infections have been described.

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Pathogenesis of Crimean-Congo hemorrhagic fever

The pathogenesis of Crimean-Congo hemorrhagic fever is similar to other viral hemorrhagic fevers. Characteristic features include the development of intense viremia, thrombocytopenia, lymphopenia in the acute stage of the disease, as well as an increase in AST, as with most viral hemorrhagic fevers, a less pronounced increase in ALT. In the terminal stage, liver and kidney failure, acute cardiovascular failure are observed. Autopsy reveals eosinophilic infiltration in the liver without a pronounced inflammatory reaction, necrotic changes in the spleen and lymph nodes. Massive bleeding may develop. DIC syndrome is recorded in the terminal phase, its genesis is unclear. As with other viral hemorrhagic fevers, there are dystrophic processes in muscle tissue, weight loss.

Symptoms of Crimean-Congo hemorrhagic fever

The incubation period of Crimean-Congo hemorrhagic fever after a bite of an infected tick lasts 1-3 days, after contact with blood or infected tissues it can be delayed to a maximum of 9-13 days. Symptoms of Crimean-Congo hemorrhagic fever vary from mild to severe.

The initial period of the disease lasts 3-6 days. The acute onset of the disease is characterized by high temperature with chills. The following symptoms of Crimean-Congo hemorrhagic fever appear: headache, pain in muscles and joints, in the abdomen and lower back, dry mouth, dizziness. Sometimes there is a sore throat, nausea, vomiting, diarrhea. Excitement and sometimes aggressiveness of patients, photophobia, rigidity and soreness of the occipital muscles often occur.

After 2-4 days from the onset of the disease, agitation is replaced by fatigue, depression, drowsiness. Pain in the right hypochondrium appears, the liver enlarges. When examining patients, hyperemia of the face, neck, shoulder girdle and mucous membranes of the oral cavity, decreased blood pressure, and a tendency to bradycardia are noted. On the 3rd-5th day of the disease, a "cut" in the temperature curve is possible, which usually coincides with the appearance of bleeding and hemorrhages. Later, a second wave of fever develops.

The peak period corresponds to the following 2-6 days. Hemorrhagic reactions develop in various combinations, the degree of expression of which varies widely from petechial exanthema to profuse cystic bleeding and determines the severity and outcome of the disease. The condition of patients deteriorates sharply. During their examination, attention is drawn to pallor, acrocyanosis, progressive tachycardia and arterial hypotension, depressed mood of patients. Lymphadenopathy may appear. Enlargement of the liver is often found, sometimes jaundice of a mixed nature (both hemolytic and parenchymatous) occurs. In 10-25% of cases, convulsions, delirium, coma develop, meningeal symptoms appear.

Convalescence begins after 9-10 days of illness and takes a long time, up to 1-2 months; asthenia can persist for up to 1-2 years.

Complications of Crimean-Congo hemorrhagic fever are varied: thrombophlebitis, pneumonia, pulmonary edema, severe gastrointestinal bleeding, acute liver and/or kidney failure, infectious toxic shock. Mortality varies from 4% to 15-30% and usually occurs in the second week of the disease.

Diagnostics of Crimean-Congo hemorrhagic fever

Differential diagnostics of Crimean-Congo hemorrhagic fever in the initial period presents great difficulties. At the height of the disease, Crimean-Congo hemorrhagic fever is differentiated from other infections that occur with hemorrhagic syndrome. The most indicative clinical signs of the disease are fever (often two-wave) and pronounced hemorrhagic manifestations.

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Laboratory diagnostics of Crimean-Congo hemorrhagic fever

Laboratory diagnostics of Crimean-Congo hemorrhagic fever is carried out in specialized laboratories with an increased level of biological protection. Characteristic changes in the hemogram are pronounced leukopenia with a shift to the left, thrombocytopenia, and increased ESR. Hypoisosthenuria and microhematuria are determined in the urine analysis. It is possible to isolate the virus from the blood or tissues, but in practice the diagnosis is more often confirmed by the results of serological reactions (ELISA, RSK, RNGA, NRIF). IgM antibodies in ELISA are determined within 4 months after the disease, IgG antibodies - within 5 years. It is possible to determine the virus antigens in ELISA. In recent years, a polymerase chain reaction (PCR) has been developed to determine the virus genome.

Treatment of Crimean-Congo hemorrhagic fever

Hospitalization and isolation of patients are mandatory. Treatment of Crimean-Congo hemorrhagic fever is carried out in accordance with the general principles of therapy of viral hemorrhagic fevers. In some cases, a positive effect was noted from the introduction of 100-300 ml of immune serum of convalescents or 5-7 ml of hyperimmune equine immunoglobulin. In some cases, a good effect can be obtained from the use of ribavirin intravenously and orally (see Lassa fever).

Prevention of Crimean-Congo hemorrhagic fever

When hospitalizing patients, it is necessary to strictly follow the requirements for the prevention of nosocomial infections and personal prevention of employees, and exercise caution when performing invasive procedures. Persons who have come into contact with the patient's blood and secretions, as well as with autopsy material, are given specific immunoglobulin as emergency prevention. Deratization and acaricidal measures in natural foci are of little effect, since carriers are numerous and widespread. Particular attention is paid to protecting people from ticks. Personal prevention measures include wearing protective clothing, impregnating clothing, tents, and sleeping bags with repellents. According to epidemiological indications, it is recommended to use a formalin-inactivated vaccine from the brain of infected white mice or suckling rats, but a reliable and effective vaccine against Crimean-Congo fever does not yet exist.

Healthcare workers who have been in contact with sick or suspected persons, as well as their biomaterial, must be monitored for three weeks with daily thermometry and careful recording of possible symptoms of Crimean-Congo hemorrhagic fever. Disinfection is carried out in the outbreak, and contact persons are not separated.