Development of a Scale for Objective Assessment of Tick Numbers as an Element of Analysis of a Tularemia Focus (Using the Example of the Dzhungar Focus)

Ixodidae ticks are the main reservoir and vector of the tularemia pathogen (Francisella tularensis), ensuring the long-term persistence of natural foci of the foothill-stream type. Given the micro-focal structure of the Dzhungar focus, the lack of a standardized scale of vector abundance limits the capability to accurately predict epizootic activity. The aim of this study was to develop an objective regional scale for grading the abundance of pasture ticks and to conduct a retrospective analysis of the relationship between their abundance and the intensity of tularemia epizootics in the Dzhungar focus. Materials and methods. The results of 270 counts of adult ticks of the genus Dermacentor, Ixodes, Hyalomma and Haemaphysalis (the “flag-hour” method), conducted in 2010–2025, were analyzed. Statistical processing was performed using PAST 4.11 and Microsoft Excel software. To construct a 5-level gradation scale (from “very low” to “very high”), we used a logarithmic data transformation followed by quintile analysis to stabilize the variance of the non-parametric sample. Results and discussion. The abundance distribution was found to be characterized by pronounced right-sided asymmetry (range – 0–156 individuals/flag-hour, median 17.0, mean 23.9). The developed scale allowed us to classify abundance as follows: <8 (very low), 8–13 (low), 13.1–22 (medium), 22.1–38 (high), and >38 (very high). A retrospective analysis revealed a paradox: maximum epizootic activity (isolation of 32 F. tularensis strains in 2018) was observed at “medium” vector abundance, while only sporadic occurrences were recorded at “very high” abundance (2022 and 2025). Hypotheses regarding increased mortality of infected specimens and the presence of specific tick haplotypes in high-infestation zones are discussed.

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