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Tick-borne encephalitis: an overview
Last reviewed: 23.04.2024
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Tick-borne encephalitis (spring-summer encephalitis, taiga encephalitis, Russian encephalitis, Far Eastern encephalitis, tick-borne encephalomyelitis) is a natural focal viral infectious disease with a transmissible mechanism of transmission of the pathogen, characterized by fever and primary lesion of the central nervous system.
ICD-10 codes
A84.0. Far Eastern tick-borne encephalitis (Russian spring-summer encephalitis).
A84.1. Central European tick-borne encephalitis.
Epidemiology of tick-borne encephalitis
Tick-borne encephalitis is a natural focal disease. Strains of the Central European variant are common in Europe to the territory of Siberia. Ural-Siberian and East-Siberian genotypes of the virus prevail over the Ural ridge, in the Far East - the Far Eastern variant. With the genetic diversity of the causative agent, it is likely that differences in the clinical picture of tick-borne encephalitis in Europe, Siberia and the Far East are associated.
The main reservoir and vector of the virus in nature are Ixodes persulcatus Ixodes, Ixodes ricinus with transphase (larva-nymph-imago) and transovarial transmission of the pathogen. Additional reservoirs of the virus are rodents (chipmunk, field mouse), rabbits, hedgehogs, birds (thrush, goldfinch, tapeworm, finch), predators (wolf, bear), large wild animals (elk, deer). Susceptible to tick-borne encephalitis virus and some agricultural animals, among which goats are most sensitive. Due to the fact that the range of reservoir hosts is quite wide, a continuous circulation of the virus occurs in nature.
The tick is infected by a virus when bitten by mammals in the viral phase. The main path of human infection is transmissible transmission through tick bites. The risk of infection of people is closely related to the activity of ticks. The seasonal peak of this activity depends on the climatic features of the geographical regions, but is maximum in spring and summer (from April to August). People with an age of 20-60 are more often ill. In the structure of the diseased, urban residents are now predominant. It is also possible to transmit the virus in an alimentary way (when raw milk of goats and cows are eaten), as well as as a result of crushing the tick when it is removed from the human body and, finally, by an aerosol path in case of violation of working conditions in laboratories.
The susceptibility to tick-borne encephalitis is high, regardless of gender and age, especially among people who first visit the natural hearth. In indigenous people, subclinical forms of infection prevail (one clinical case for 60 inpatients).
Immunity after endured tick-borne encephalitis is persistent, lifelong. In the blood of those who have recovered throughout life, viral neutralizing antibodies are retained.
The patient as a source of infection for others is not dangerous.
[What causes tick-borne encephalitis?
Tick-borne encephalitis is caused by tick-borne encephalitis virus, which belongs to the Flaviviridae family . A virus with a size of 45-50 nm consists of a nucleocapsid with a cubic type of symmetry and is coated with a shell. Nucleocapsid contains RNA and protein C (core). The envelope consists of two glycoproteins (membrane M, shell E) and lipids.
The virus of tick-borne encephalitis is cultivated in chick embryos and cultures of tissues of various origins. With prolonged passage, the pathogenicity of the virus is reduced. Among laboratory animals, white mice, rat suckers, hamsters and monkeys are most susceptible to infection with the virus, among the domestic animals are sheep, goats, pigs, horses. The virus is unequally resistant to various environmental factors: it boils for 2-3 minutes during boiling, it breaks easily during pasteurization, treatment with solvents and disinfectants, but it is capable of long-term viability at low temperatures and in a dried state. The virus survives long enough in such foods as milk or oil, which can sometimes be sources of infection. The virus is resistant to the action of low concentrations of hydrochloric acid, so the food path of infection is possible.
Pathogenesis of tick-borne encephalitis
After the introduction, tick-borne encephalitis virus locally multiplies in skin cells. Degenerative-inflammatory changes develop on the site of the bite in the tissues. With the alimentary route of infection, virus fixation occurs in the epithelial cells of the gastrointestinal tract.
The first wave of viralemia (transient) is caused by the penetration of the virus into the blood from the sites of primary localization. At the end of the incubation period, a second wave of viremia occurs, coinciding with the onset of the virus multiplication in the internal organs. The final phase is the introduction and replication of the virus in the cells of the central nervous system and the peripheral nervous system.
What are the symptoms of tick-borne encephalitis?
The incubation period of tick-borne encephalitis during infection through a tick bite is 5-25 (on average 7-14) days, and at the food path of infection - 2-3 days.
The course of tick-borne encephalitis can be erased, light, of medium severity and severe.
According to the nature of the current distinguish between acute, two-wave and chronic (progredient) flow.
Tick-borne encephalitis, regardless of form, in most cases begins acutely. Rarely there is a period of prodromes lasting 1-3 days.
Feverish form of tick - borne encephalitis is recorded in 40-50% of cases. In most patients, the tick-borne encephalitis disease begins acutely. The febrile period lasts from several hours to 5-6 days. In the acute period of the disease, the body temperature rises to 38-40 ° C and above. Sometimes a two-wave or even a three-wave fever is observed.
Where does it hurt?
How is tick-borne encephalitis diagnosed?
The diagnosis of "tick-borne encephalitis" is based on anamnestic, clinical epidemiological and laboratory data. Great importance in endemic regions is attached to visits to forests, a park, summer cottage in the spring and summer, the fact of sucking a tick, and eating unboiled goat or cow's milk.
On examination, attention is drawn to the presence of hyperemia of the face, neck and upper body, injection of vessels of sclera, conjunctivitis and hyperemia of the oropharynx. Patients are flaccid, adynamic. It is necessary to carefully inspect the skin, since spots or different sizes of hyperemic spots may remain at the site of suction of the mites. All patients need to explore the neurological status.
What do need to examine?
How to examine?
What tests are needed?
How is tick-borne encephalitis treated?
Strict bed rest is shown, regardless of the general condition and state of health during the entire febrile period and 7 days after the temperature normalization. A special diet is not required (common table). During the feverish period, abundant drinking is recommended: fruit drinks, juices, bicarbonate mineral waters.
Etiotropic treatment of tick-borne encephalitis is prescribed to all patients with tick-borne encephalitis, regardless of whether there was an inoculation against tick-borne encephalitis or was used with the preventive purpose of an antiancephalitic immunoglobulin.
What prognosis does tick-borne encephalitis have?
In most cases, tick-borne encephalitis results in recovery. In the convalescent period in 20-50% of cases, the asthenic state of various duration develops - from several weeks to several months.
In focal forms, patients in most cases are disabled.