Tick-borne encephalitis virus

Tick-borne encephalitis is an infectious disease that is registered in Russia from the Maritime Territory to the western borders in the forest zone, i.e., the habitats of the carriers - ixodids. As an independent nosological unit was isolated in 1937 as a result of work in the Siberian taiga complex expedition, headed by LA Zilber. The expedition included prominent virologists (MP Chumakov, VD Soloviev), clinicians, epidemiologists. Within 3 months. The viral nature of the disease was established , the features of the virus and the main epidemiological patterns, including natural focality, seasonality in connection with the activity of ticks, were determined. Simultaneously, the features of the clinic and pathomorphology of tick-borne encephalitis have been described, some ways of prevention and therapy have been developed. Further studies of this disease showed its prevalence not only in our country, but also abroad. Since the isolation of the tick-borne encephalitis virus, more than 500 strains have been found. In terms of the degree of pathogenicity for mice, the relation to fibroblast tissue cultures of chick embryos and other indicators, they were divided into 3 groups. The third group includes weakly virulent strains.

According to the type of vector, there are two main types of tick-borne encephalitis virus: persulcate, eastern (Ixodes persukatus) and castor, western (vector Ixodes ricinus). The study of the nucleotide sequence of genomic RNA in representatives of the eastern and western types of the virus revealed 86-96% homology in them. In recent years, the third type of virus has been isolated from Greece from the mites Rhipicephalus bursa. According to the clinical course, there are two main variants of the disease: eastern, leaking heavier, and western, having a lighter flow.

In about 80% of cases, infection occurs by transmissible transmission with a tick bite and in 20% by nutritional intake of raw goat, cow or sheep milk. There are also cases of laboratory infection. Children of pre-school and school age, as well as workers of geological parties, are more often ill.

The incubation period is from 1 to 30 days, usually 7-12 days after the tick sucking. The onset of the disease is usually acute: chills, severe headache, fever rise to 38-39 ° C, nausea, sometimes vomiting, muscle pain, twitching, meningeal signs develop.

There are three main forms of tick-borne encephalitis - febrile, meningeal and focal. The febrile form is 30-50%, there are no signs of meningitis, the outcome is favorable, asthenia is rarely observed. The meningeal form accounts for 40-60% of the incidence, is characterized by meningeal syndrome with changes in cerebrospinal fluid, fever can have a two-wave character.

Focal forms are observed less often (8-15%), characteristic signs are meningeal symptoms and focal lesions of the nervous system of different degree of severity, accompanied by paralysis, loss of sensitivity and other neurological symptoms, damage to the brain stem, which leads to impaired respiratory and cardiac activity. Mortality is high, after the illness there are persistent complications.

Laboratory diagnosis is carried out mainly by virological and serological methods. The virus is secreted from the blood, liquor, urine, less often nasopharyngeal swabs, feces and sectional material when infected with cell cultures. The virus is typified in various variants of the biological neutralization reaction of the virus. With a serological method, antibodies specific for the virus in DSC, neutralization, RTGA, and immunosorbent reactions are detected.

Treatment is symptomatic. To prevent the disease, vaccination against tick-borne encephalitis is used in the form of a killed culture vaccine.