Etiological Structure, Clinical and Epidemiological Characteristics of Infections Transmitted by Ixodic Ticks in the Sverdlovsk Region at the Present Stage

Abstract

Relevance. The Sverdlovsk region is a highly endemic territory for infections transmitted by ixodic ticks. The possibilities of laboratory diagnostics of tick–borne infections in the routine practice of a clinician in the region today are limited mainly by testing blood serum for antibodies to the tick-borne encephalitis virus (TBE virus) and Lyme disease (LD) pathogens – Borrelia burgdorferi sensu lato complex, therefore, among tick-borne infections in the region currently mainly TBE and LD are registered. In case of negative results for antibodies to the pathogens of the above infections, the diagnosis may remain unknown. Aims. To study the etiological structure of infections transmitted by ixodic ticks in the Sverdlovsk region at the present stage, as well as to characterize the epidemiological and clinical features of the course of tick-borne infections detected in conditions of a combination of natural foci. Materials and methods. The study included 227 patients undergoing inpatient or outpatient treatment during the epidemic season of tick activity in 2021 (June-August) at LLS MO "New Hospital" (Urban Center of Natural Focal Infections). The case histories (epidemiological, clinical and laboratory indicators) were studied from each patient, as well as the material (blood) was examined prospectively and retrospectively using molecular biological (PCR) and serological (ELISA, planar protein biochip) methods. Results and discussion. During the study, six diseases were identified among the examined patients: TBE, LD (erythematous and nonerythematous forms), Borrelia miyamotoi disease (BMD), human granulocytic anaplasmosis (HGA), human monocytic ehrlichiosis (HME), as well as "Viral fever transmitted by arthropods" (VFTA). Among the examined patients, the proportion of patients with monoinfection was 49,5%, with mixed infection – 50,5%. Additional studies conducted by us using specific PCR for the presence DNA rickettsia and the causative agent of Q-fever in the blood of patients gave negative results. The general epidemiological characteristics for the above identified infections were the vector-borne mechanism, the prevalence of diseases in groups of middle-aged and elderly people, the largest number of cases of infection with pathogens of any tick-borne infection occurred in Yekaterinburg and its surroundings, for all infections, the duration of tick bite in most cases did not exceed one day; there were differences by sex, incubation period. Clinical symptoms were similar, except for the erythematous form of LD (the presence of erythema migrans at the byte site of tick), because the vast majority of patients had a general infectious syndrome; general laboratory indicators varied. Confirmation of the diagnosis was based on the results of the complex application of molecular biological and serological research methods. Conclusions. The modern etiological structure of infections transmitted by ixodic ticks in the Sverdlovsk region is represented not only by TBE and LD, but also by new disease to our country, such as BMD, HGA, HME, while a high proportion of mixed infections in various combinations has been revealed.