1,721,091 research outputs found
On the optimal control of SIR model with Erlang-distributed infectious period: isolation strategies
No full textMathematical models are formal and simplified representations of the knowledge related to a phenomenon. In classical epidemic models, a major simplification consists in assuming that the infectious period is exponentially distributed, then implying that the chance of recovery is independent on the time since infection. Here, we first attempt to investigate the consequences of relaxing this assumption on the performances of time-variant disease control strategies by using optimal control theory. In the framework of a basic susceptible–infected–removed (SIR) model, an Erlang distribution of the infectious period is considered and optimal isolation strategies are searched for. The objective functional to be minimized takes into account the cost of the isolation efforts per time unit and the sanitary costs due to the incidence of the epidemic outbreak. Applying the Pontryagin’s minimum principle, we prove that the optimal control problem admits only bang–bang solutions with at most two switches. In particular, the optimal strategy could be postponing the starting intervention time with respect to the beginning of the outbreak. Finally, by means of numerical simulations, we show how the shape of the optimal solutions is affected by the different distributions of the infectious period, by the relative weight of the two cost components, and by the initial conditions
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Understanding the dynamics of West Nile virus in Emilia-Romagna, Italy
Full text linkWest Nile Virus (WNV) has been identified for the first time in Italy in 1998, and more
continuously since 2008 with a total of 173 neurological human cases between 2008 and 2015.
Still the circulation of the virus appears to have been episodic with most cases concentrated in a
few years and a few hotspots shifting in different years.
The region Emilia Romagna, which is one of the most affected areas, has set up since 2009 a
systematic program of mosquito and corvids (known to be among the most competent bird
species for WNV) trapping and testing. Data collected through this program have been analysed
through a mathematical model in order to understand the main drivers of the observed
dynamics.
The analysis has mainly been based on an SIR (for competent birds)-SI (mosquitoes) model,
with an environmentally driven population model, validated on independent data [1], for
mosquito dynamics, and a simple population model for bird dynamics, in which the free
parameters were the mosquito biting rate and the host-vector ratio.
Our results showed that simplest models with constant mosquito feeding behaviours are
incompatible with the observed seasonal patterns of infected mosquitoes and birds. On the
other hand, including a seasonal shift in mosquito feeding behaviour, as proposed in [2] and
confirmed also for Italy in [3], makes model outputs much more consistent with observed data.
Other improvements of the model allow for the age structure of the bird population, or for the
presence of other untested competent bird species. Finally, multi-year simulations of a spatiallystructured
model show a qualitative agreement with observed patterns of spatial spread.
Our findings can be of particular interest for public health policy makers, as they provide
important insights on WNV dynamics in order to improve surveillance, and risk assessment of
WNV in the area
Dynamics of a metapopulation epidemic model with localized culling
No full textA two-patches metapopulation mathematical model, describing the dynamics of Susceptibles and Infected in wildlife diseases, is presented. The two patches are identical in absence of control, and culling activities are performed in only one of them. Firstly, the dynamics of the system in absence of control is investigated. Then, two types of localized culling strategies (proactive end reactive) are considered. The proactive control is modeled by a constant culling effort, and for the ensuing model the disease free equilibrium is characterized and existence of the endemic equilibrium is discussed in terms of a suitable control reproduction number. The localized reactive control is modeled by a piecewise constant culling effort function, that introduces an extra-mortality when the number of infected individuals in the patch overcomes a given threshold. The reactive control is then analytically and numerically investigated in the frame of Filippov systems. We find that localized culling may be ineffective in controlling diseases in wild populations when the infection affects host fecundity in addition to host mortality, even leading to unexpected increases in the number of infected individuals in the nearby areas
Dynamics of a metapopulation epidemic model with localized culling
Full text linkA two-patches metapopulation mathematical model, describing the dynamics of Susceptibles and Infected in wildlife diseases, is presented. The two patches are identical in absence of control, and culling activities are performed in only one of them. Firstly, the dynamics of the system in absence of control is investigated. Then, two types of localized culling strategies (proactive end reactive) are considered. The proactive control is modeled by a constant culling effort, and for the ensuing model the disease free equilibrium is characterized and existence of the endemic equilibrium is discussed in terms of a suitable control reproduction number. The localized reactive control is modeled by a piecewise constant culling effort function, that introduces an extra-mortality when the number of infected individuals in the patch overcomes a given threshold. The reactive control is then analytically and numerically investigated in the frame of Filippov systems. We find that localized culling may be ineffective in controlling diseases in wild populations when the infection affects host fecundity in addition to host mortality, even leading to unexpected increases in the number of infected individuals in the nearby areas
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