Tick-borne encephalitis - Diagnosis

Diagnostics of tick-borne encephalitis is based on anamnestic, clinical-epidemiological and laboratory data. In endemic regions, great importance is attached to visiting a forest, park, or summer cottage in the spring and summer, the fact of tick bite, and also the consumption of unboiled goat or cow milk.

Indications for consultation with other specialists

All patients with tick-borne encephalitis are subject to mandatory consultation with a neurologist. Patients with progressive tick-borne encephalitis receive outpatient and inpatient care from a neurologist; if necessary, infectious disease specialists are involved for consultations.

Indications for hospitalization

All patients with suspected tick-borne encephalitis are subject to hospitalization in a specialized infectious diseases department with an intensive care unit.

Clinical diagnostics of tick-borne encephalitis

Early clinical diagnostic symptoms of tick-borne encephalitis are an increase in body temperature to 39-40 °C, chills, headache, dizziness, nausea, vomiting, general weakness, pain in the muscles, joints, and lower back.

During examination, attention is paid to the presence of hyperemia of the face, neck and upper body, injection of scleral vessels, conjunctivitis and hyperemia of the oropharynx. Patients are lethargic and adynamic. It is necessary to carefully examine the skin, since dots or hyperemic spots of various sizes may remain at the site of tick attachment. All patients need to be examined for neurological status.

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Specific and non-specific laboratory diagnostics of tick-borne encephalitis

In the peripheral blood, moderate lymphocytic leukocytosis is detected, sometimes a shift to the left with an increase in the number of band neutrophils, and an increase in ESR.

In the two-wave course of the disease, the first wave of the disease is characterized by leukopenia with relative lymphocytosis in most patients. During the second wave, leukocytosis with a neutrophilic shift and an increase in ESR is observed. In meningeal and focal forms of the disease, lymphocytic pleocytosis is detected in the cerebrospinal fluid, from several dozen to several hundred cells in 1 μl.

Laboratory diagnostics of tick-borne encephalitis is based on the detection of antibodies in the blood of patients. RSK, RTGA, RN and other methods are used.

Standard for diagnostics of tick-borne encephalitis

The diagnostic standard is ELISA, which allows for the separate determination of the total pool of antibodies to the virus, immunoglobulins of class G and M. Determination of immunoglobulins of class M is important for the diagnosis of not only acute cases of the disease, but also exacerbations of the chronic course. Immunoglobulins of class G are a consequence of the disease or effective vaccination. Serological studies are carried out in paired sera taken at the beginning and end of the disease. In the absence of antibodies, it is possible to study the 3rd blood sample taken 1.5-2 months after the onset of the disease.

In recent years, the PCR method has been introduced into clinical practice, which allows for the detection of specific fragments of the virus genome in the blood and cerebrospinal fluid at early stages of the disease. The method allows for a diagnosis to be made within 6-8 hours.

Example of diagnosis formulation

A84.0. Tick-borne encephalitis, meningeal form, moderate severity (PCR of cerebrospinal fluid is positive).

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Differential diagnostics of tick-borne encephalitis

Differential diagnosis of tick-borne encephalitis is carried out with three main groups of diseases:

• other transmissible infections carried by ticks;
• infectious diseases with acute onset and pronounced general infectious manifestations;
• other neuroinfections.

In regions where tick-borne encephalitis is endemic, other transmissible infections are usually encountered: systemic tick-borne borreliosis and tick-borne rickettsiosis. These infections have in common a history of a tick bite, approximately the same incubation periods, and the presence of symptoms of intoxication in the acute period.

Simultaneous infection (from 0.5 to 5-10%) with tick-borne encephalitis pathogens and borrelia of ticks I. persulcatus determines the existence of associated natural foci of these infections and the possibility of developing signs of both diseases in one patient, i.e. mixed infection. To diagnose mixed infection, the presence of clinical signs of two infections is mandatory. The diagnosis of tick-borne encephalitis is based on the characteristic clinical picture of the disease and the detection of IgM or increasing IgG titers to the tick-borne encephalitis virus in the blood serum. The diagnosis of tick-borne borreliosis is based on the clinical picture (erythema migrans, Bannwarth syndrome, facial nerve neuritis, polyradiculoneuropathy, myocarditis, polyarthritis) and the determination of diagnostic IgM titers to Borrelia burgdorferi in the blood serum or an increase in IgG titers in ELISA.

Differential diagnostics of tick-borne encephalitis with influenza should take into account the seasonality of the disease, visiting a forest, contact with ticks or hypothermia, as well as the results of laboratory tests.

Hemorrhagic fever with renal syndrome differs from tick-borne encephalitis in excruciating pain in the lumbar region, pronounced changes in the clinical blood test (from the 3rd to 5th day of illness, neutrophilic leukocytosis, shift in the leukocyte formula to the left, the appearance of plasma cells, an increase in ESR to 40-60 mm/h) and the development of renal failure, characterized by oliguria, low relative density of urine, proteinuria.

When conducting differential diagnostics of meningeal forms of tick-borne encephalitis with meningitis caused by other viruses (Coxsackie, ECHO, mumps, influenza, herpes viruses), it is necessary to pay attention first of all to the seasonality of the disease and an indication in the anamnesis of visiting a forest, bites and attacks by ticks. Along with the clinical symptoms of the disease, methods of virological and serological studies of blood serum are of great importance.

Tuberculous meningitis is characterized by a prodromal period, gradual development of meningeal symptoms with involvement of cranial nerves in the process. As meningeal symptoms increase, lethargy and adynamia increase, patients gradually fall into a soporous state. Excitement is rare. Headache is pronounced. Cerebrospinal fluid flows under high pressure; lymphocytic pleocytosis; protein content is increased, glucose is decreased. Formation of a delicate film in the cerebrospinal fluid is characteristic, sometimes with the presence of Mycobacterium tuberculosis, which finally clarifies the diagnosis. X-ray examination often reveals various changes in the lungs of a tuberculous nature. Tuberculosis is often found in the patient's history or in his environment.

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