The spread of tick-borne encephalitis (TBE) represents an important threat to human and animal health in many places of Eurasia. TBE enzootic cycles are strongly influenced by the non-systemic transmission of the infection between ticks co-feeding on the same rodent host. In this context, the frequency distribution of ticks on rodents plays a crucial role in amplifying TBE virus (TBEv) transmission. Here we analysed a 9-year time series (from 2000 to 2008) of Ixodes ricinus ticks (main TBE vector in Europe) feeding on Apodemus flavicollis mice (main TBE reservoir-competent host) sampled in a TBE focus in Trentino (Northern Italy). The tail of the distribution of the number of ticks per host was fitted by two theoretical distributions: the widely used Negative Binomial (NB) and the power-law (PL). In order to investigate the effect of different tail of tick distribution on the persistence and spread of a non-systemically transmitted pathogen, we simulated, through a stochastic network model, the transmission of TBEv between susceptible and infective ticks considering only co-feeding transmission. The dynamics of tick-host interaction is included in model simulations by distributing ticks on mice, independently from their epidemic state, accordingly to both fitted distributions. Empirical distribution of feeding ticks on mice was skewed and heavy-tailed. The fit with theoretical distributions indicated that the tail of tick infestation pattern on rodents is better described by PL distribution rather than by NB distribution. Model simulations indicated different outcomes of disease spreading when considering different distribution laws of ticks among hosts. Specifically, we found that the probability of pathogen persistence and spread was higher when the tail of the distribution is described by a PL distribution. In conclusion, our results suggest that the heterogeneity of the number of ticks feeding on rodents strongly influences the spreading of non-systematically transmitted tick-borne pathogens

Ferreri, L.; Giacobini, M.; Bajardi, P.; Bertolotti, L.; Bolzoni, L.; Rizzoli, A.; Rosa', R. (2013). Pattern of tick aggregation on rodents: larger than expected tail distribution enhances the spread of tick-borne pathogens. In: Epidemics4 - Fourth International Conference on Infectious Disease Dynamics, Amsterdam, The Nederlands, 19-22 November 2013. handle: http://hdl.handle.net/10449/23487

Pattern of tick aggregation on rodents: larger than expected tail distribution enhances the spread of tick-borne pathogens

Rizzoli, Annapaola;Rosa', Roberto
2013-01-01

Abstract

The spread of tick-borne encephalitis (TBE) represents an important threat to human and animal health in many places of Eurasia. TBE enzootic cycles are strongly influenced by the non-systemic transmission of the infection between ticks co-feeding on the same rodent host. In this context, the frequency distribution of ticks on rodents plays a crucial role in amplifying TBE virus (TBEv) transmission. Here we analysed a 9-year time series (from 2000 to 2008) of Ixodes ricinus ticks (main TBE vector in Europe) feeding on Apodemus flavicollis mice (main TBE reservoir-competent host) sampled in a TBE focus in Trentino (Northern Italy). The tail of the distribution of the number of ticks per host was fitted by two theoretical distributions: the widely used Negative Binomial (NB) and the power-law (PL). In order to investigate the effect of different tail of tick distribution on the persistence and spread of a non-systemically transmitted pathogen, we simulated, through a stochastic network model, the transmission of TBEv between susceptible and infective ticks considering only co-feeding transmission. The dynamics of tick-host interaction is included in model simulations by distributing ticks on mice, independently from their epidemic state, accordingly to both fitted distributions. Empirical distribution of feeding ticks on mice was skewed and heavy-tailed. The fit with theoretical distributions indicated that the tail of tick infestation pattern on rodents is better described by PL distribution rather than by NB distribution. Model simulations indicated different outcomes of disease spreading when considering different distribution laws of ticks among hosts. Specifically, we found that the probability of pathogen persistence and spread was higher when the tail of the distribution is described by a PL distribution. In conclusion, our results suggest that the heterogeneity of the number of ticks feeding on rodents strongly influences the spreading of non-systematically transmitted tick-borne pathogens
2013
Ferreri, L.; Giacobini, M.; Bajardi, P.; Bertolotti, L.; Bolzoni, L.; Rizzoli, A.; Rosa', R. (2013). Pattern of tick aggregation on rodents: larger than expected tail distribution enhances the spread of tick-borne pathogens. In: Epidemics4 - Fourth International Conference on Infectious Disease Dynamics, Amsterdam, The Nederlands, 19-22 November 2013. handle: http://hdl.handle.net/10449/23487
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