Tick-borne encephalitis is an infectious disease based on damage to the brain and spinal cord by a flavivirus transmitted to humans by the bites of ixodic ticks. Depending on the form of the disease, its manifestations are fever, headache, convulsions, vomiting, impaired coordination of movements, pain along the nerves, sluggish paresis and paralysis. The diagnosis is confirmed by PCR of blood and cerebrospinal fluid. Treatment in the early stages of the disease consists in the appointment of immunoglobulin against tick-borne encephalitis, antiviral drugs. In the later stages, it is only possible to prevent life-threatening conditions and symptomatic treatment.
A84 Tick-borne viral encephalitis
Tick-borne encephalitis (spring-summer tick-borne meningoencephalitis) is a viral disease (viral encephalitis) that is transmitted to humans through the bites of ixodic ticks, characterized by damage to the brain and spinal cord. The main area of its distribution is China, Mongolia. However, outbreaks of the disease are also observed in the forest areas of Eastern Europe and the Scandinavian Peninsula.
Tick-borne encephalitis refers to the so-called transmissible infections, that is, those that are transmitted to humans through blood-sucking insects. Every year, approximately 5-6 thousand cases of this infectious disease are registered in the United States.
The causative agent of the disease is a virus from the genus of flaviviruses (Flavivirus). In the images from an electron microscope, it represents particles in the form of a ball with small protrusions on the surface, measuring 40-50 nm. Such a small size (2 times smaller than the influenza virus and 3-4 times smaller than the measles virus) allows the pathogen to easily penetrate all the protective barriers of the immune system.
The features of the tick-borne encephalitis virus are weak resistance to high temperatures, disinfectants and ultraviolet radiation. So, when boiling, it dies after 2 minutes and cannot be preserved in the environment in hot sunny weather. However, at low temperatures, it is able to maintain viability for a long time. In infected dairy products, flavivirus does not lose its properties for 2 months.
In nature, the tick-borne encephalitis virus, as the name of the disease implies, is found in the body of ixodic ticks. In addition to humans, the virus can infect wild and domestic animals, including cows and goats. Therefore, infection can occur both directly – when a person is bitten by a tick or accidentally crushed by an insect when trying to extract it, and when using milk and dairy products that have not undergone heat treatment and received from sick animals. The longer the tick is on a person’s skin, the higher the risk of developing the disease.
The largest number of cases of the disease is recorded in late spring and early autumn, this is due to an increase in the number of ticks at this time. You can get infected with the tick-borne encephalitis virus while walking in the forest, park, visiting outdoor recreation areas.
Depending on which signs of the disease are most pronounced, tick-borne encephalitis can occur in 3 forms:
- febrile (with a predominance of fever), develops in 50%
- of meningeal patients (with lesions of the membranes of the brain and spinal cord), characteristic of 30% of infected
- focal (when brain matter is involved in the process with the development of focal neurological symptoms), it is noted in 20% of patients.
The latent, or incubation period of the disease lasts about 1-2 weeks. But there can be both lightning-fast, when 24 hours pass from the moment of infection to the first signs, and protracted forms of the disease, with an incubation period lasting up to 1 month.
During the latent period, viral particles multiply intensively at the site of introduction (skin wound or intestinal wall), then enter the bloodstream and with it spread throughout the body. It is this moment that marks the appearance of the first clinical symptoms. The second peak of flavivirus reproduction occurs already in the internal organs (central nervous system, kidneys, lymph nodes, liver).
All forms of tick-borne encephalitis (febrile, meningeal, focal) have common initial signs. The disease begins acutely, in many cases the patient can clearly indicate even the hour when his condition deteriorated sharply. The first symptoms resemble flu manifestations: chills, muscle aches, arthralgia, headache, weakness, lethargy, vomiting and convulsions may occur against the background of a sharp rise in body temperature (typical for children). During the examination, attention is drawn to the redness of the skin of the face, neck up to the collarbones, the whites of the eyes with dilated blood vessels. The subsequent course of the disease directly depends on the form in which it will occur in a particular patient.
Tick-borne encephalitis in this form occurs with a predominance of a febrile condition, which can last from 2 to 10 days. In most cases, it is of a wave nature, that is, after the first rise in temperature and the subsequent subsiding of clinical manifestations, the disease seems to return again and a new attack of fever follows, lasting several days. After about 10 days, the body temperature returns to normal, the general condition of the patient improves. However, weakness, lack of appetite, palpitations, sweating can be observed for another 1 months after laboratory recovery (according to the results of blood and cerebrospinal fluid tests).
This form is characterized by the appearance on the 3-4 day of the disease of signs of meningitis – lesions of the membranes of the spinal cord and brain. It is manifested by the following symptoms: severe headache, which is not relieved by painkillers; vomiting, hypersensitivity of the skin, when even touching clothes to the body causes pain; rigidity (strong tension) of the occipital muscles, which leads to involuntary tilting of the head back; Kernig’s symptom is the inability to arbitrarily straighten the knee leg bent at right angles in the knee and hip joint in the supine position; Brudzinsky’s upper and lower symptoms are when the doctor tries to tilt the patient’s head forward (chin to chest) and when pressing on the pubis, reflex flexion of the legs occurs in the knee and hip joints.
All these manifestations of the disease are united by the concept of meningeal syndrome and mean that the tick-borne encephalitis virus has reached the membranes of the spinal cord and brain. Fever and meningeal symptoms last for about 2 weeks. After normalization of temperature in patients for a long time (up to 2 months), asthenia (weakness, lethargy), poor tolerance of bright light, loud sounds, depressed mood persists.
It belongs to the most severe and most unfavorable forms of tick-borne encephalitis according to the prognosis. It is based on the penetration of the pathogen into the substance of the brain and spinal cord. It is characterized by a sharp increase in body temperature to 40 ° C and above, there is lethargy, drowsiness (hypersomnia), vomiting, convulsions, chills.
There are symptoms of damage to the substance of the brain with the appearance of hallucinations, disorders of consciousness, delirium, impaired perception of time and space. When the brain stem is involved in the process, in which the centers responsible for providing vital functions are located, respiratory and cardiac disorders may occur. When the virus enters the cerebellar tissue, a violation of the sense of balance develops, trembling in the hands and feet. When the spinal cord is affected, sluggish (with reduced muscle tone) paresis and paralysis of the muscles of the neck, shoulders, upper chest and supra-scapular area occur. When the virus penetrates into the roots of the spinal cord, sciatica occurs – pain along the nerve, violation of voluntary movements, functions of internal organs, the appearance of disorders of skin sensitivity in those departments for which the affected root is responsible.
The focal form of tick-borne encephalitis can be of a two-wave nature (two-wave viral meningoencephalitis), when the first attack of the disease is similar to the usual febrile form, and a few days after the normalization of body temperature, symptoms of damage to the substance of the brain and spinal cord appear sharply.
A special form of tick-borne encephalitis is progredient, which can develop after any other form of the disease. It is characterized by the development of persistent disorders of the functions of the brain and spinal cord several months or even years after the acute period of the disease.
In establishing an accurate diagnosis, an important role is played by: clinical manifestations; epidemiological data; laboratory studies.
- Clinical manifestations. These are the characteristics of the disease that a neurologist describes when examining a patient. Clinical manifestations include patient complaints containing features of the onset of the disease, the sequence of occurrence of certain symptoms; an objective examination that reveals signs of damage to organs and systems.
- Epidemiological data. This is information about the patient’s place of residence, his professional activity, the consumption of certain products, the season in which the disease occurred, the fact of a tick bite and attempts to extract it from the skin independently. These data help to narrow down the range of suspected diseases.
- Laboratory tests. To confirm the cause of the disease, the detection of tick-borne encephalitis virus particles in the blood and cerebrospinal fluid using PCR (polymerase chain reaction) is used. In addition, serological methods can be used to determine the titer of antibodies in paired sera of the patient taken at intervals of 2 weeks. This takes into account not only the level of antibody titer in one sample, but also its increase or decrease depending on the time elapsed from the onset of the disease.
Treatment is carried out exclusively in the hospital. Since a person is a dead end in the spread of flavivirus, a patient with tick-borne encephalitis is not contagious and does not pose a danger to others, therefore all therapeutic measures are carried out not in the infectious department, but in neurology.
Treatment includes specific (directed at the pathogen), pathogenetic (blocking the mechanisms of disease development) and symptomatic therapy. The patient is assigned strict bed rest. The scheme of specific treatment depends on the time that has elapsed since the appearance of the first symptoms. At the very beginning of the disease (the first week), the administration of anti-tick immunoglobulin to patients showed high efficiency. It is administered within 3 days. Also, with early diagnosis, the use of antiviral drugs gives good results: ribonuclease, ribavirin, interferon, potato shoot extract.
All these drugs are ineffective in the later stages of the disease, when the virus has already affected the central nervous system. In this case, the treatment is not aimed at combating the causative agent of the disease, but at pathological mechanisms that threaten the patient’s life. To do this, oxygen is supplied through a mask, a ventilator for respiratory disorders, diuretics to reduce intracranial pressure, drugs that increase the resistance of the brain to oxygen starvation, neuroleptics.
The prognosis for tick-borne encephalitis depends on the degree of damage to the nervous system. With a febrile form, as a rule, all patients recover completely. In the meningeal form, the prognosis is also favorable, however, in some cases, persistent complications from the central nervous system in the form of chronic headaches, the development of migraines may be observed. The focal form of tick-borne encephalitis is the most unfavorable according to the prognosis. Mortality can reach 30 people per 100 cases. Complications of this form are the occurrence of persistent paralysis, convulsive syndrome, and a decrease in mental abilities.
Prevention of tick-borne encephalitis is divided into 2 areas: organizational measures and vaccination. Organizational measures consist in teaching residents of endemic regions (places of spread of the disease) to comply with the rules for visiting forest areas and outdoor recreation areas during the period of tick activity: dressing clothes covering most of the body (with long sleeves and trousers, panama hats or caps on the head); thorough examination of clothing and body for the detection of live ticks; immediate medical attention in case of detection of a suckling insect; warning about the inadmissibility of self-removal of the attached tick from the skin; application of repellents on clothes before walking; mandatory boiling of milk, purchase of dairy products only from official manufacturers.
Vaccination includes: passive immunization – administration of immunoglobulin to patients who have not previously been vaccinated against tick–borne encephalitis (in the case of a tick bite) and active immunization – vaccinations to residents of the area of the spread of the disease 1 month before the season of tick activity.