[Possibilities of serological verification of siberian tick borne type with use of test system for identification of antibodies to Rickettsia conorii.]

The real epidemiological impact of Spotted Fever Group rickettsioses including Siberian tick-borne typhus (STT) in Russia is not sufficiently studied. One of the reasons is the actual absence of either certified domestic diagnostic kits or the evidence for using foreign test kits for laboratory verification of this group of tick-borne infections in medical practice. Objective of our study was to study the diagnostic accuracy of the ELISA test system based on Rickettsia conorii antigens for serological verification of STT. The ROC analysis was performed and operational characteristics (sensitivity, specificity, accuracy, likelihood ratio of positive and negative results) of the STT serological verification test to identify IgM to rickettsia at different times from the onset of the disease using a test system to detect antibodies to Rickettsia conorii were calculated based on the results of a survey of two groups of patients comparable by gender and age (34 patients with pathognomonic signs of STT and 76 clinically healthy people). It was found that the detection of IgM antibodies to rickettsia using the Rickettsia conorii IgM/IgG ELISA test system (Vircell) allows the disease to be verified 10-14 days after the onset of clinical symptoms in 72% (56-88%) of STT patients. We recommend the interpretation of results of the test system "Rickettsia conorii ELISA IgM/IgG" for serological verification of STT which differ from the manufacturer's recommendations regarding verification of Mediterranean fever caused by R. conorii in the following way: the diagnosis of STT should be considered laboratory confirmed when the index of IgM antibodies (IAT) exceeds 8.0; if the IAT is less than 5.0 then a repeated examination of the patient after 10-14 days will be necessary; if the IAT is in the range of 5.0-8.0 then the sample should be re-examined and / or the patient should be examined after 10-14 days. The use of the test system "Rickettsia conorii ELISA IgM / IgG" is promising for laboratory diagnosis and seroepidemiological studies of Spotted Fever Group rickettsioses in Russia.

[Clinical and laboratory diagnosis of tick-borne rickettsioses in areas of low risk of infection Rickettsia sibirica.]

For the first time, a comparative description of clinical and laboratory parameters in patients with clinical signs of tick-borne rickettsiosis in a natural focus with a low risk of infection with R. sibirica and circulation of R. raoultii is given, depending on the results of serological verification of the diagnosis. Established almost complete coincidence of clinical and laboratory parameters in patients with tick-borne rickettsiosis, regardless of the presence of antibodies to R. sibirica and / or R. raoultii. It was shown that even the complex use of complement fixation test, indirect immunofluorescent test and ELISA for the detection of antibodies to R. sibirica does not allow verification of the diagnosis in a third part of patients with pathognomonic signs of tickborne rickettsiosis. In seropostive patients, antibodies to R. sibirica prevailed, which makes it impossible to differentiate cases of tick-borne rickettsiosis of different species etiology. The possible reasons of the phenomenon of «seronegativeness¼ of patients with tick-borne rickettsiosis and approaches to its study are discussed. It is concluded that with the existing diversity and insufficient knowledge of rickettsiae circulating in natural foci, and the current state of laboratory diagnostics, the basis for the diagnosis of «Tick-borne rickettsiosis¼ should be the clinical and epidemiological signs of this infectious disease, which must be recorded in the established order even no serological verification. For such cases, ICD-10 has two encoding options: A 79.9 - Rickettsiosis, unspecified (infection caused by rickettsia, no other indication) and A 77.9 - Spotted fever, unspecified (tick-borne fever, no other indication) [mkb-10.com].

[Evaluation of the effectiveness of the serological methods for the identification of antibodies in patients with tissue ricketsiosis on the territories of a different risk of Rickettsia sibirica infection.]

Cases of tick-borne rickettsiosis in Siberia and the Far East are associated with R. sibirica, the causative agent of Siberian tick typhus (STT). In connection with a sharp reduction in the nomenclature of diagnostic products and an increase in the spectrum of species of founding rickettsiae on the territory of Russia, new approaches to the laboratory verification of diagnoses are needed. We present an evaluation of the effectiveness of serological research methods (complement fixation test, indirect immunofluorescence, and ELISA) in patients with tick-borne rickettsioses in areas of different risk of infection with R. sibirica. Patients were diagnosed with STT from the highly endemic territory of the Altai Republic and from the Naziayevsky district of the Omsk region, where natural foci of rickettsioses of the spotted fever group was detected with the circulation of two species of pathogenic rickettsia, R. sibirica and R. raoultii. As a control group, samples of sera from epidemic seasons from clinically healthy people in Omsk were used. To verify the diagnosis of Siberian tick typhus, the use of serological methods is most appropriate, of which the most sensitive is ELISA, which allows detecting antibodies at an earlier time. In the ELISA for confirmation of the diagnosis, the first serum can be examined only on IgM. Investigation of the 2nd serum should be performed in ELISA for the presence of IgM and IgG antibodies with R. sibirica antigen. Reaction of indirect immunofluorescence (RNIF) for the study of paired sera should be conducted with specific antigens of rickettsia circulating in this focus. In laboratories not equipped for setting ELISA, it was recommended to use CFT. When the titer increases in two or more times and IgM and IgG are detected in the second serum, taking into account clinical manifestations, the diagnosis of "Siberian tick typhus" can be considered confirmed.