219 research outputs found
Non-systemic transmission of tick-borne diseases: a network approach
Tick-Borne diseases can be transmitted via non-systemic (NS) transmission.
This occurs when tick gets the infection by co-feeding with infected ticks on
the same host resulting in a direct pathogen transmission between the vectors,
without infecting the host. This transmission is peculiar, as it does not
require any systemic infection of the host. The NS transmission is the main
efficient transmission for the persistence of the Tick-Borne Encephalitis virus
in nature. By describing the heterogeneous ticks aggregation on hosts through a
\hyphenation{dynamical} bipartite graphs representation, we are able to
mathematically define the NS transmission and to depict the epidemiological
conditions for the pathogen persistence. Despite the fact that the underlying
network is largely fragmented, analytical and computational results show that
the larger is the variability of the aggregation, and the easier is for the
pathogen to persist in the population.Comment: 15 pages, 4 figures, to be published in Communications in Nonlinear
Science and Numerical Simulatio
Interplay of network dynamics and ties heterogeneity on spreading dynamics
The structure of a network dramatically affects the spreading phenomena
unfolding upon it. The contact distribution of the nodes has long been
recognized as the key ingredient in influencing the outbreak events. However,
limited knowledge is currently available on the role of the weight of the edges
on the persistence of a pathogen. At the same time, recent works showed a
strong influence of temporal network dynamics on disease spreading. In this
work we provide an analytical understanding, corroborated by numerical
simulations, about the conditions for infected stable state in weighted
networks. In particular, we reveal the role of heterogeneity of edge weights
and of the dynamic assignment of weights on the ties in the network in driving
the spread of the epidemic. In this context we show that when weights are
dynamically assigned to ties in the network an heterogeneous distribution is
able to hamper the diffusion of the disease, contrary to what happens when
weights are fixed in time.Comment: 10 pages, 10 figure
Modeling the effects of variable feeding patterns of larval ticks on the transmission of Borrelia lusitaniae and Borrelia afzelii
Spirochetes belonging to the Borrelia burgdoferi sensu lato (sl) group cause
Lyme Borreliosis (LB), which is the most commonly reported vector-borne
zoonosis in Europe. B. burgdorferi sl is maintained in nature in a complex
cycle involving Ixodes ricinus ticks and several species of vertebrate hosts.
The transmission dynamics of B. burgdorferi sl is complicated by the varying
competence of animals for different genospecies of spirochetes that, in turn,
vary in their capability of causing disease. In this study, a set of difference
equations simplifying the complex interaction between vectors and their hosts
(competent and not for Borrelia) is built to gain insights into conditions
underlying the dominance of B. lusitaniae (transmitted by lizards to
susceptible ticks) and the maintenance of B. afzelii (transmitted by wild
rodents) observed in a study area in Tuscany, Italy. Findings, in agreement
with field observations, highlight the existence of a threshold for the
fraction of larvae feeding on rodents below which the persistence of B. afzelii
is not possible. Furthermore, thresholds change as nonlinear functions of the
expected number of nymph bites on mice, and the transmission and recovery
probabilities. In conclusion, our model provided an insight into mechanisms
underlying the relative frequency of different Borrelia genospecies, as
observed in field studies.Comment: 14 pages, 3 figures, to be published in Theoretical Population
Biolog
Complex and dynamic population structures: synthesis, open questions, and future directions
The population structure of an evolutionary algorithm influences the dissemination and mixing of advantageous alleles, and therefore affects search performance. Much recent attention has focused on the analysis of complex population structures, characterized by heterogeneous connectivity distributions, non-trivial clustering properties, and degree-degree correlations. Here, we synthesize the results of these recent studies, discuss their limitations, and highlight several open questions regarding (1) unsolved theoretical issues and (2) the practical utility of complex population structures for evolutionary search. In addition, we will discuss an alternative complex population structure that is known to significantly influence dynamical processes, but has yet to be explored for evolutionary optimization. We then shift our attention toward dynamic population structures, which have received markedly less attention than their static counterparts. We will discuss the strengths and limitations of extant techniques and present open theoretical and experimental questions and directions for future research. In particular, we will focus on the prospects of "active linking,” wherein edges are dynamically rewired according to the genotypic or phenotypic properties of individuals, or according to the success of prior inter-individual interaction
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