Tick-borne encephalitis - Symptoms.

The incubation period for tick-borne encephalitis when infected through a tick bite is 5-25 (on average 7-14) days, and when infected through food, it is 2-3 days.

The main symptoms of tick-borne encephalitis and the dynamics of their development

Tick-borne encephalitis, regardless of its form, begins acutely in the vast majority of cases. Rarely, a prodromal period lasting 1-3 days occurs.

The febrile form of tick-borne encephalitis is registered in 40-50% of cases. In most patients, the disease begins acutely. The febrile period lasts from several hours to 5-6 days. During the acute period of the disease, the body temperature rises to 38-40 °C and higher. Sometimes two-wave and even three-wave fever is observed.

Patients are concerned about the following symptoms of tick-borne encephalitis: headache, general weakness, malaise, chills, feeling of heat, sweating, dizziness, pain in the eyeballs and photophobia, loss of appetite, pain in the muscles, bones, spine, upper and lower extremities, lower back, neck and joints. Nausea is characteristic, vomiting is possible for one or more days. Also noted are injection of the vessels of the sclera and conjunctiva, hyperemia of the face, neck and upper half of the body, pronounced hyperemia of the mucous membranes and oropharynx. In some cases, pallor of the skin is noted. Meningism is possible. In this case, inflammatory changes in the cerebrospinal fluid are absent.

In most cases, tick-borne encephalitis ends with complete clinical recovery. However, in some patients, asthenovegetative syndrome persists after discharge from the hospital.

The meningeal form is the most common form of tick-borne encephalitis. It accounts for 50-60% of the morbidity structure. The clinical picture is characterized by pronounced general infectious and meningeal symptoms.

In most cases, the onset of the disease is acute. The body temperature rises to high values. The fever is accompanied by chills, a feeling of heat and sweating. Headaches of varying intensity and localization are characteristic. Anorexia, nausea and frequent vomiting are noted. In some cases, myasthenia, pain in the eyeballs, photophobia, unsteady gait and hand tremors are expressed.

On examination, hyperemia of the face, neck and upper body, injection of the vessels of the sclera and conjunctiva are revealed.

Meningeal syndrome is detected in half of the patients upon admission. In the rest, it develops on the 1st to 5th day of hospital stay. Transient disorders caused by intracranial hypertension are detected; facial asymmetry, anisocoria, failure to bring the eyeballs outward, nystagmus, increased or decreased tendon reflexes, anisoreflexia.

Cerebrospinal fluid pressure is usually elevated (250-300 mm H2O). Pleocytosis ranges from several dozen to several hundred cells per 1 μl of cerebrospinal fluid. Lymphocytes predominate, and neutrophils may predominate in the early stages. Cerebrospinal fluid glucose levels are normal. Changes in the cerebrospinal fluid persist for a relatively long time: from 2-3 weeks to several months.

Asthenovegetative syndrome persists longer than in the febrile form. Irritability and tearfulness are characteristic. The benign course of the meningeal form of tick-borne encephalitis does not exclude the possibility of the further development of the clinical picture of the chronic form of the disease.

The meningoencephalitic form is characterized by a severe course and high mortality. The frequency of this form in certain geographic regions is from 5 to 15%. The acute period of the disease is characterized by such symptoms of tick-borne encephalitis as: high temperature, more pronounced intoxication, pronounced meningeal and general cerebral symptoms, as well as signs of focal brain damage.

The encephalitic form is characterized by a combination of general cerebral and focal symptoms. Depending on the predominant localization of the pathological process, bulbar, pontine, mesencephalic, subcortical, capsular, hemispheric syndromes occur. Disturbances of consciousness are possible, epileptic seizures are frequent.

Profound disturbances of consciousness up to the development of coma are characteristic. In patients admitted in an unconscious and soporous state, motor excitation, convulsive syndrome, muscle dystonia, fibrillary and fascicular twitching in individual muscle groups are observed. Nystagmus is often detected. The appearance of subcortical hyperkinesis, hemiparesis, as well as damage to the cranial nerves are characteristic: III, IV, V, VI pairs, somewhat more often VII, IX, X, XI and XII pairs.

In case of brainstem lesions, bulbar and bulbopontine syndromes appear, less often - symptoms of midbrain damage. Swallowing disorders, choking, nasal tone of voice or aphonia, paralysis of the tongue muscles are noted, when the process spreads to the bridge - symptoms of damage to the nuclei of the VII and VI cranial nerves. Mild pyramidal signs, increased reflexes, clonus, pathological reflexes are often detected. Brainstem lesions are extremely dangerous due to the possible development of respiratory and cardiac disorders. Bulbar disorders are one of the main causes of high mortality in the meningoencephalitic form of tick-borne encephalitis.

When examining the cerebrospinal fluid, lymphocytic pleocytosis is detected. The protein concentration is increased to 0.6-1.6 g/l.

Hemiplegia occupies a special place among focal lesions of the nervous system. In the first days of the febrile period (more often in older people), a central type of hemiplegia syndrome develops, resembling vascular lesions of the nervous system (strokes) in its course and localization. These disorders are often unstable and already in the early period have a tendency to reverse development. Asthenovegetative syndrome develops in 27.3-40.0% of patients. Residual effects include paresis of the facial nerves.

Poliomyelitis is the most severe form of infection. It was most common in previous years, and is currently observed in 1-2% of patients. This form has a high rate of disability among patients.

The neurological status is characterized by significant polymorphism. Patients with the poliomyelitis form of the disease may experience sudden weakness in one limb or numbness in it. Later, motor disorders develop in these limbs. Against the background of fever and general cerebral symptoms, the following symptoms of tick-borne encephalitis develop: flaccid paresis of the cervical-brachial muscles and upper limbs. Paresis is often symmetrical and affects the entire neck muscles. The raised arm falls passively, the head hangs on the chest. Tendon reflexes are not evoked. At the end of the second week, atrophy of the affected muscles develops. Paresis and paralysis of the lower limbs are rare.

The course of the disease is always severe. Improvement of the general condition occurs slowly. Only half of the patients have moderate recovery of lost functions. Pleocytosis from several hundred to a thousand cells per 1 μl is detected in the CSF.

Residual effects in the poliomyelitis form are characteristic of all patients. Weakness of the neck and upper limb muscles, the symptom of a "drooping" head, paresis of the upper limb muscles, hypotrophy of the neck muscles, shoulder girdle, forearms, and intercostal muscles are noted.

The polyradiculoneuritic form is diagnosed in 1-3% of patients. The leading symptoms are mononeuritis (of the facial and sciatic nerves), cervical-brachial radiculoneuritis, and polyradiculoneuritis with or without ascending course. The symptoms of tick-borne encephalitis of this form are as follows: neuralgia, radicular symptoms, muscle and nerve pain, peripheral paralysis or paresis. Patients experience pain along the nerve trunks, paresthesia (feeling of "crawling ants", tingling).

Two-wave fever occurs in all forms of the disease, but more often in the meningeal form. This type of fever is more typical for diseases caused by the Central European and East Siberian genotypes of the virus. The first fever wave requires the presence of a pronounced infectious toxic syndrome. There is an acute onset, a sudden increase in temperature to 38-39 ° C, accompanied by headache and general weakness. After 5-7 days, the condition of the patients improves, the body temperature normalizes, but after a few days it rises again. Often, against the background of the second wave, meningeal syndrome appears in patients.

Chronic progressive course is observed in 1-3% of patients. Chronic forms occur several months and sometimes years after the acute period of the disease, mainly in meningoencephalitic, less often meningeal forms of the disease.

The main clinical form of the chronic period is Kozhevnikov epilepsy, which is expressed in constant myoclonic hyperkinesis, primarily affecting the muscles of the face, neck, and shoulder girdle. Periodically, especially under emotional stress, paroxysmal intensification and generalization of myoclonus or their transition to a large tonic-clonic seizure with loss of consciousness occurs. Also observed is the syndrome of chronic subacute poliomyelitis, caused by slowly progressive degeneration of the peripheral motor neurons of the anterior horns of the spinal cord, which is clinically characterized by increasing atrophic paresis of the limbs, mainly the upper ones, with a constant decrease in muscle tone and tendon reflexes.

Hyperkinetic syndrome is characterized by the appearance of spontaneous rhythmic muscle contractions in individual muscle groups of paretic limbs already in the acute period of the disease. Often, progressive forms are accompanied by mental disorders up to dementia. Often, clinical symptoms are mixed, when the progression of hyperkinesis is combined with increasing amyotrophy and, sometimes, mental disorders. As the severity of symptoms increases, patients become disabled.

In recent years, severe clinical forms of the acute period have been observed relatively rarely, which does not exclude the further development of a chronic progressive form of the disease.

Course and prognosis of tick-borne encephalitis

Symptoms of tick-borne encephalitis increase over 7-10 days. Then focal symptoms of tick-borne encephalitis begin to weaken, general cerebral and meningeal symptoms gradually disappear. In the meningeal form, recovery occurs in 2-3 weeks without consequences. Asthenic syndrome may remain for several months. In the poliomyelitis form, complete recovery without neurological disorders does not occur, atrophic paresis and paralysis, mainly of the cervical myotomes, persist.

In the encephalitic form, impaired functions are restored slowly. The recovery period can last from several months to 2-3 years. The most severe course is noted in the meningoencephalitic form with a violent onset, a rapidly developing comatose state and a fatal outcome. High mortality (up to 25%) occurs in the encephalitic and poliomyelitis forms with bulbar disorders.

In recent decades, due to extensive preventive measures, the course of tick-borne encephalitis has changed. Severe forms have become much less common. Mild symptoms of tick-borne encephalitis, meningeal and febrile forms with a favorable outcome predominate.

Classification of tick-borne encephalitis

The clinical classification of tick-borne encephalitis is based on the determination of the form, severity and nature of the course of the disease. Forms of tick-borne encephalitis:

• inapparent (subclinical):
• feverish;
• meningeal;
• meningoencephalitic;
• poliomyelitis;
• polyradiculoneuritic.

The course of tick-borne encephalitis can be latent, mild, moderate or severe.

Depending on the nature of the course, a distinction is made between acute, two-wave and chronic (progressive) course.

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Mortality and causes of death

Mortality in tick-borne encephalitis is associated with the development of bulbar and convulsive-comatose syndromes. The frequency of fatal outcomes depends on the genotype of the circulating virus and varies from isolated cases in Europe and the European part of Russia to 10% in the Far East.