Synchrony of Sylvatic Dengue Isolations: A Multi-Host,Multi-Vector SIR Model of Dengue Virus Transmission in Senegal

Isolations of sylvatic dengue-2 virus from mosquitoes,humans and non-human primates in senegal show synchronized multi-annual dynamics over the past 50 years. host demography has been shown to directly affect the period between epidemics in other pathogen systems,therefore,one might expect unsynchronized multi-annual cycles occurring in hosts with dramatically different birth rates and life spans. however,in senegal,we observe a single synchronized eight-year cycle across all vector species,suggesting synchronized dynamics in all vertebrate hosts. in the current study,we aim to explore two specific hypotheses: 1) primates with different demographics will experience outbreaks of dengue at different periodicities when observed as isolated systems,and that coupling of these subsystems through mosquito biting will act to synchronize incidence; and 2) the eight-year periodicity of isolations observed across multiple primate species is the result of long-term cycling in population immunity in the host populations. to test these hypotheses,we develop a multi-host,multi-vector susceptible,infected,removed (sir) model to explore the effects of coupling multiple host-vector systems of dengue virus transmission through cross-species biting rates. we find that under small amounts of coupling,incidence in the host species synchronize. long-period multi-annual dynamics are observed only when prevalence in troughs reaches vanishingly small levels (<10-10),suggesting that these dynamics are inconsistent with sustained transmission in this setting,but are consistent with local dengue virus extinctions followed by reintroductions. inclusion of a constant introduction of infectious individuals into the system causes the multi-annual periods to shrink,while the effects of coupling remain the same. inclusion of a stochastic rate of introduction allows for multi-annual periods at a cost of reduced synchrony. thus,we conclude that the eight-year period separating amplifications of dengue may be explained by cycling in immunity with stochastic introductions. © 2012 althouse et al.