Brandenburg et al.
Seroprevalence of tick-borne encephalitis (TBE) virus antibodies in wild rodents from two natural TBE foci in Bavaria, Germany.
Pathogens. 2023;12(2):185. doi: 10.3390/pathogens12020185

TBE virus is maintained in complex natural endemic transition cycles, so-called microfoci, which may be rather small (may be smaller than a football ground, 0.5–1 ha), involving ticks as vectors. In Central Europe, Ixodes ricinus is the main vector transmitting TBE virus to a naïve host after a blood meal on a viremic host. The main mammalian hosts are rodents like the bank vole Clethrionomys glareolus and the yellow-necked mouse Apodemus flavicollis.

In a four-year study from 2019–2022, the rodent population in well-described TBE foci located in Bavaria, Germany, was serologically monitored for TBE antibodies using a capture-recapture method. Overall, 706 captures of small rodents were documented corresponding to 500 different individuals, and 100 individuals were re-captured 128 times.

TBE antibodies were detected in 17% of all investigated samples – about 19% in bank voles and 11% in the yellow-necked mouse. Antibodies persisted for a long time in mice, perhaps life-long. A higher percentage of positive TBE antibodies were revealed in male mice than in female mice, and this relation was also observed in adult mice compared to juvenile mice. No significant annual or seasonal differences were observed during the study period.

The movement of the mice was limited to a defined small area because recaptured animals were never identified more than 40 m away from the first capture. Thus, it was concluded that the virus cycle between juvenile ticks and rodents occurs in small areas with an average size of about 0.5 to 1 ha forming a natural focus. From these microfoci, infected adult ticks are transported by larger wild animals to other locations where a new microfocus can be established if appropriate biotic and abiotic conditions exist.

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