Clinical and laboratory characteristics of tick-borne encephalitis in the Novosibirsk region in 2024 with identifi cation of severity predictors

Introduction. Tick-borne encephalitis (TBE) is a transmissible disease endemic for the Novosibirsk region (NR). The incidence of TBE in the NR is 2,7–5,8 times higher than the Russian average. Despite the fact that the infection is vaccine-preventable, fatal cases are recorded in the NR year after year. Western Siberia is characterized by the circulation of the Siberian subtype of the virus, which affects the central nervous system (CNS) in two-thirds of cases, and in 20–30% of cases, manifestations are focal, with a high risk of mortality or permanent disability.

Aim. To analyze cases of TBE in patients of Novosibirsk City Infectious Diseases Clinical Hospital No. 1 (CIDCH) and to establish factors influencing the form and severity of the disease in unvaccinated patients, as well as predictors of the early prognosis of unfavorable severe TBE.

Materials and methods . Clinical, epidemiological, and laboratory data were analyzed in 68 patients diagnosed with TBE, hospitalized at CIDCH in 2024. Febrile TBE was recorded in 32% of patients, meningeal TBE – in 41,5%, and focal TBE – in 26,5%. The diagnosis of TBE was verified by detecting immunoglobulin M and G antibodies to the TBE virus using enzyme-linked immunosorbent assay. The results of a complete blood count (CBC), biochemistry for inflammatory markers, and cerebrospinal fluid analysis were estimated in all patients, as well as levels of serum and cerebrospinal fluid of interleukin-6 (IL-6) and ferritin were measured.

Results . The average age of patients with the febrile form of TBE was 48 ± 4,2 years. All patients had fever and intoxication. The CBC showed leukocytosis in 27,3% of patients, and absolute lymphopenia in 36,3%. Elevated C-reactive protein (CRP) levels were found in more than half of patients (54,5%). The average age of patients with the meningeal form of TBE was 50,3 ± 5,4 years. The majority of patients (86%) had high fever, while low fever was observed in 4 patients. Severe intoxication and general cerebral syndromes were detected in 93% of cases; the cerebrospinal fluid analysis revealed lymphocytic pleocytosis in 83,3% of patients – from 16 to 648 cells/ml. Leukocytosis was found in 57% of cases, and absolute lymphopenia – in only 14,3% of patients. An increase in CRP values   was observed in 13 people, and ferritin – in only 4 people. Among patients with focal forms of TBE, men predominated (77,8%); the average age was 49,7 ± 5,1 years. The meningoencephalo-poliomyelitic form of TBE was diagnosed in 61,1% of patients, while the rest had the meningoencephalitic form of TBE. A fatal outcome was recorded in 3 patients. The CBC revealed leukocytosis in 89% of cases, and absolute lymphopenia in 33%. CRP and ferritin levels were elevated in only half of the patients. Lumbar puncture results revealed pleocytosis – from 100 to 537 cells/μl, neutrophilic in 27,8%. Cerebrospinal fluid IL-6 was significantly elevated – up to 600–800 pg/ml.

Conclusion. In unvaccinated patients with TBE, age, time limits for seeking medical care, leukocyte count, lymphopenia, peripheral blood hematocrit, and CRP levels did not correlate with disease severity. Duration and grade of fever, as well as leukocytosis and blood IL-6 levels differed significantly between patients without and with CNS involvement. Pleocytosis levels   were significantly higher in patients with focal TBE. Increased cerebrospinal fluid IL-6 levels were observed in severe cases, as well as a direct correlation with pleocytosis levels, which most reliably reflects the severity of CNS involvement in TBE and may predict an unfavorable course of TBE. The identified predominance of males among patients with focal TBE, as well as late seroconversion in a significant proportion of patients, require further study in a larger patient population.

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