Omsk hemorrhagic fever

Omsk hemorrhagic fever (OHF) is an acute viral zoonotic natural focal disease with a transmissible mechanism of pathogen transmission, characterized by undulating fever, general intoxication, development of hemorrhagic syndrome and vegetative-vascular dystonia, as well as damage to the central nervous system, lungs, kidneys and a relatively benign course.

ICD-10 code

A98.1. Omsk hemorrhagic fever.

Epidemiology of Omsk hemorrhagic fever

The main source and reservoir of the virus are the ixodid ticks Dermacentor pictus and Dermacentor marginatus (the virus is transmitted transovarially and during metamorphosis). In addition, rodents infected with the Omsk hemorrhagic fever virus (voles, mice, rats, shrews, muskrats, chipmunks, water rats and other rodents) are found in natural foci. People are infected mainly through tick bites, as well as by airborne dust from rodents, by contact - when cutting up animal carcasses and by alimentary - when drinking raw lake water. The natural susceptibility of people is high: the virus affects all age groups of the population, but mainly people aged 20-40 years old (mainly industrial workers and people engaged in field work in forest-steppe regions) fall ill. Natural foci of Omsk hemorrhagic fever are known in Omsk and Tyumen. Orenburg, Kurgan, Novosibirsk regions, as well as in the north of Kazakhstan. The seasonality of the disease is clearly expressed: the first increase is observed in the spring-summer months (May-June) - the period of tick activity (transmissive transmission route): the second - in the autumn months (September-October) during the muskrat catching period (non-transmissive transmission route).

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What causes Omsk hemorrhagic fever?

Omsk hemorrhagic fever is caused by an arbovirus of the Flariviridae family, Flavivirus genus. The genome is single-stranded RNA; its antigenic structure is similar to that of tick-borne encephalitis virus. According to electron microscopy, the virion size is up to 40 nm; it is spherical, cubic in symmetry; covered with a bilayer membrane containing lipids and proteins that have antigenic properties and determine group- and species-specific determinants. The Omsk hemorrhagic fever virus reproduces in the cytoplasm on the membranes of the Golgi complex. It is highly pathogenic for white mice, muskrats and narrow-skulled voles: it causes paralytic phenomena in some monkey species after intracerebral infection. It is well cultivated in cell cultures of mouse, chicken, hamster, monkey and human embryonic tissue, but a pronounced cytopathogenic effect is only seen in pig embryonic tissue cultures. The Omsk hemorrhagic fever virus becomes highly virulent when passed on white mice and muskrats; it poses a risk of intra-laboratory infection for employees working with infected animals. The virus is inactivated by disinfectant solutions (3% carbolic acid solution, 3% lysol solution, 1% chloramine solution); at a temperature of 70-80 °C it dies after 10 minutes; when boiled - instantly; at 4 °C it is inactivated after 29 days; in 50% glycerol it survives up to 7 months; in a dried state - up to 4 years.

Pathogenesis of Omsk hemorrhagic fever

Omsk hemorrhagic fever has not been studied enough. Penetrating the human body through damaged skin, mucous membranes of the respiratory tract and digestive organs, the virus spreads throughout the body with the bloodstream and affects mainly the endothelium of the vessels of the microcirculatory bed, the adrenal glands, the autonomic nervous system and the spleen. Damage to small blood vessels in various organs and tissues causes the development of hemorrhagic syndrome.

Symptoms of Omsk hemorrhagic fever

The incubation period for Omsk hemorrhagic fever is 2-10 days (on average 5-7).

Symptoms of Omsk hemorrhagic fever give reason to distinguish:

• typical forms of the disease (hemorrhagic);
• atypical forms of the disease (without hemorrhagic manifestations).

According to the severity of the disease, the following are distinguished:

• mild flow;
• moderate course;
• severe course.

According to the nature of clinical manifestations, the following are distinguished:

• acute course (without relapse):
• acute recurrent course (with repeated temperature wave).

Omsk hemorrhagic fever begins acutely, suddenly, with high fever, chills, severe headache, dizziness, severe weakness, muscle pain in the limbs and back, nausea and nosebleeds. Body temperature from the first day of the disease reaches high values (39-40 ° C), lasts for 3-4 days, and then on the 7th-15th day of the disease lytically decreases. Almost 50% of patients during the recovery period (on the 2nd-3rd week of the disease) are found to have a second wave of fever, during which the symptoms of Omsk hemorrhagic fever resume with deterioration in condition. The second wave of the disease lasts 4-14 days but is milder. Against the background of fever, patients are lethargic, lie motionless with their heads thrown back, inhibited, reluctant to answer questions. Puffiness and hyperemia of the face, neck; injection of blood vessels of the sclera and conjunctiva; bright color of the soft and hard palate, gums with the development of small and large hemorrhages on them. From the 3rd-4th day of the disease, hemorrhagic symptoms of Omsk hemorrhagic fever develop, the earliest of which is the appearance of a hemorrhagic rash on the anterior and lateral surfaces of the chest, extensor surfaces of the arms and legs; positive symptoms of a tourniquet and a pinch. Nasal, pulmonary, gastrointestinal and uterine bleeding are possible, often not profuse, but recurring several times during the disease. During an exacerbation, general cerebral and meningeal symptoms of Omsk hemorrhagic fever, transient focal clinical manifestations are sometimes detected. Respiratory system lesions in the form of bronchitis and small focal pneumonia are often detected, which is a characteristic feature of the clinical picture of Omsk hemorrhagic fever (unlike other hemorrhagic fevers). Diuresis is reduced, but the development of renal failure is not detected. Involvement of the digestive system organs is expressed by nausea, vomiting, bitterness and dryness in the mouth, hepatomegaly, and pain in the epigastrium. Reversible changes in the cardiovascular system are characteristic in the form of bradycardia, expansion of the heart borders to the left, muffled heart sounds, and arterial hypotension. The course of the convalescence period depends on the presence of a repeated febrile wave and complications.

Complications of Omsk hemorrhagic fever

Omsk hemorrhagic fever rarely has complications. Complications include otitis or parotitis (often purulent), pyelitis, late focal pneumonia. Most patients with Omsk hemorrhagic fever end in complete recovery. In uncomplicated cases, the prognosis is favorable.

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Mortality and causes of death

In severe cases, death may occur early as a result of intoxication or bleeding and on the 30th-45th day of the disease from septic complications. Mortality does not exceed 1%.

Diagnosis of Omsk hemorrhagic fever

Clinical symptoms of Omsk hemorrhagic fever:

• Acute onset with a sharp rise in body temperature, myalgia; bronchitis and pneumonia often occur: development of hemorrhagic (petechial rash, hemorrhages in the sclera, hemoptysis: nasal, gastrointestinal, pulmonary and uterine bleeding) and meningeal syndromes in the absence of pronounced manifestations of renal failure.
• Repeated increase in body temperature during the convalescence period.
• Epidemiological history (stay in areas endemic for Omsk hemorrhagic fever, tick bite, features of professional activity).
• Seasonality.

Specific and non-specific laboratory diagnostics of Omsk hemorrhagic fever

Non-specific laboratory diagnostics of Omsk hemorrhagic fever

• Clinical blood test. Reveals increased hemoglobin content and red blood cell count, leukopenia, moderate neutrophilia with a left shift. thrombocytopenia. decreased ESR to 3-7 mm/h.
• General urine analysis. Characteristic: proteinuria, microhematuria, cylindruria, presence of granular cells of the renal epithelium and urinary tract epithelium in the urine sediment already from the 2nd day of the disease (up to 20-30 in the field of vision).

Specific laboratory diagnostics of Omsk hemorrhagic fever

• Fluorescent antibody method (in paired sera).
• PCR.

Instrumental diagnostics of Omsk hemorrhagic fever

Chest X-ray reveals a picture of interstitial pneumonia.

The electrocardiogram reveals reversible diffuse changes in the myocardium in the form of deformation and widening of the QRS complex, as well as changes in the voltage of the P and T waves.

An ultrasound of the kidneys is performed.

Differential diagnostics of Omsk hemorrhagic fever

Differential diagnostics of Omsk hemorrhagic fever is carried out with other hemorrhagic fevers, tick-borne encephalitis, and leptospirosis.

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Indications for hospitalization

Omsk hemorrhagic fever is a reason for mandatory hospitalization in an infectious diseases hospital regardless of the severity and period of the disease. Outpatient observation and treatment of patients with suspected Omsk hemorrhagic fever is unacceptable. Transportation of the patient should be as gentle as possible, excluding jolts and shaking.

Treatment of Omsk hemorrhagic fever

Drug treatment of Omsk hemorrhagic fever includes pathogenetic and symptomatic treatment.

Etiotropic treatment for Omsk hemorrhagic fever has not been developed.

Pathogenetic treatment of Omsk hemorrhagic fever

Detoxification treatment of Omsk hemorrhagic fever - intravenous administration of 5-10% glucose solutions, isotonic sodium chloride solution with ascorbic acid and cocarboxylase. Disaggregants (pentoxifylline), xanthinol nicotinate, dipyridamole, angioprotectors (calcium gluconate, etamsylate, rutoside, calcium dobesylate); fresh frozen plasma, protease inhibitors (aprotinin); antioxidants (vitamin E, ubiquinone compositum), enterosorbents (hydrolytic lignin, povidone) are used.

In case of inflammatory complications, antibiotics are prescribed: penicillins, cephalosporins, chloramphenicol, ofloxacin, ciprofloxacin.

Regime and diet

Bed rest is required.

A gentle diet is recommended - fractional, warm, with a transition to the general table (No. 15) during the convalescence period.

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Approximate periods of incapacity for work

Patients are discharged when their condition is satisfactory and laboratory parameters (clinical blood and urine tests) are normalized. The period of incapacity is determined individually. The period of release from work after discharge is: for a mild form of the disease - 7-10 days, moderate - 10-14 days, severe - 15-30 days.

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Clinical examination

All convalescents from Omsk hemorrhagic fever are subject to medical examination. The observation period for those who have recovered from a mild form of Omsk hemorrhagic fever is 3 months, and for moderate and severe forms - 12 months.

The observation is carried out by an infectious disease specialist, and in his absence - by a local therapist. The first control examination is carried out 1 month after discharge from the hospital (urine and blood are tested), the subsequent ones - after 3, 6, 9 and 12 months.

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What should the patient know?

A balanced diet is recommended, excluding irritating spicy food and alcoholic beverages; adherence to a physical regimen (contraindicated: heavy physical work, hypothermia, visiting a bathhouse, sauna, playing sports for 6-12 months). General tonics and multivitamins are prescribed.

How is Omsk hemorrhagic fever prevented?

Specific prevention of Omsk hemorrhagic fever

In outbreaks, a vaccine against tick-borne encephalitis is used (due to the similarity of the antigenic characteristics of the pathogens, a stable immunity against both diseases develops), and a killed formol vaccine from the brain of white mice infected with the Omsk hemorrhagic fever virus is also used. In emergency cases, passive immunoprophylaxis with the blood serum of convalescents is carried out in laboratories (30-50 ml intramuscularly).

Non-specific prevention of Omsk hemorrhagic fever

They carry out the destruction of ticks in nature, the fight against rodents; it is necessary to observe individual safety measures (use of protective clothing, insecticides, when working in dusty rooms - respirators).

What is the prognosis for Omsk hemorrhagic fever?

Compared with HFRS and CHF, Omsk hemorrhagic fever has a fairly favorable prognosis, which depends on compliance with the principles of hospitalization, patient care, timely and comprehensive drug treatment, and prevention of complications.