Evaluation of the Effectiveness of Methods for Detecting Francisella tularensis in the Study of Field Material and Characterization of Isolated Strains of the Pathogen

The aim of the work was to perform a comparative analysis of the informative value of diagnostic methods in the study of various environmental objects for the presence of tularemia agent markers; molecular-genetic characterization of strains of the causative agent of tularemia.
Materials and methods. A comparative analysis of effectiveness of diagnostic methods for tularemia indication: PCR (polymerase chain reaction), AbNT (antibody neutralization test), ICT (immune-chromatographic test) in various samples of field material from the foci of the Rostov Region, Lugansk People’s Republic, Donetsk People’s Republic, Zaporozhe and Kherson Regions for the period of 2020–2023 was carried out. The molecular-genetic characteristics of the strains isolated from various sources was obtained using VNTR typing followed by the construction of a dendrogram applying the NJ method.
Results and discussion. The comparative analysis of the effectiveness has shown that the biological method remains the gold standard for detecting live bacteria, Francisella tularensis, in field material. Serological methods based on the detection of specific antigens are a reliable marker of the pathogen circulation in the focus of tularemia in cases where it is not possible to isolate live culture. If the AbNT results were questionable, the samples were additionally investigated using immune-chromatographic tests. It has been established that AbNT is the most informative method when studying the material from the nesting and burrowing substrate, bird regurgitates and droppings of predatory mammals. At the same time, according to our data, PCR diagnostic methods are the most adequate ones in relation to such environmental objects as hay, grain, fodder, water, etc. The 31 F. tularensis cultures studied are represented by six individual VNTR genotypes. The largest number of genotypes (4 out of 6) was found among small mammals, two genotypes were indicated in ticks and one – in a water sample. The combined use of serological and molecular-biological methods makes it possible to increase the reliability and accuracy of detecting the causative agent of tularemia in environmental objects.

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