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Incidence from coincidence: patterns of tick infestations on rodents facilitate transmission of tick-borne encephalitis virus

Published online by Cambridge University Press:  01 February 1999

S. E. RANDOLPH
Affiliation:
Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK
D. MIKLISOVÁ
Affiliation:
Institute of Zoology, Slovak Academy of Sciences, 842 06 Bratislava, Slovakia
J. LYSY
Affiliation:
Institute of Zoology, Slovak Academy of Sciences, 842 06 Bratislava, Slovakia
D. J. ROGERS
Affiliation:
Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK
M. LABUDA
Affiliation:
Institute of Zoology, Slovak Academy of Sciences, 842 06 Bratislava, Slovakia

Abstract

Tick-borne encephalitis (TBE) virus has a highly focal distribution through Eurasia. Endemic cycles appear to depend on the transmission of non-systemic infections between ticks co-feeding on the same rodent hosts. The particular features of seasonal dynamics and infestation patterns of larval and nymphal Ixodes ricinus, but not Dermacentor reticulatus, from 4 regions within TBE foci in Slovakia, are such as to promote TBE virus transmission. The distributions of larvae and nymphs on their principal rodent hosts are highly aggregated and, rather than being independent, the distributions of each stage are coincident so that the same ca. 20% of hosts feed about three-quarters of both larvae and nymphs. This results in twice the number of infectible larvae feeding alongside potentially infected nymphs compared with the null hypothesis of independent distributions. Overall, co-feeding transmission under these circumstances brings the reproductive number (R0) for TBE virus to a level that accounts quantitatively for maintained endemic cycles. Essential for coincident aggregated distributions of larvae and nymphs is their synchronous seasonal activity. Preliminary comparisons support the prediction of a greater degree of coincident seasonality within recorded TBE foci than outside. This identifies the particular climatic factors that permit such patterns of tick seasonal dynamics as the primary predictors for the focal distribution of TBE.

Type
Research Article
Copyright
1999 Cambridge University Press

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