A Spatial Simulation Model for the Dispersal of the Bluetongue Vector Culicoides brevitarsis in Australia

Abstract

BackgroundThe spread of Bluetongue virus (BTV) among ruminants is caused by movement of infected host animals or by movement of infected Culicoides midges, the vector of BTV. Biologically plausible models of Culicoides dispersal are necessary for predicting the spread of BTV and are important for planning control and eradication strategies.MethodsA spatially-explicit simulation model which captures the two underlying population mechanisms, population dynamics and movement, was developed using extensive data from a trapping program for C. brevitarsis on the east coast of Australia. A realistic midge flight sub-model was developed and the annual incursion and population establishment of C. brevitarsis was simulated. Data from the literature was used to parameterise the model.ResultsThe model was shown to reproduce the spread of C. brevitarsis southwards along the east Australian coastline in spring, from an endemic population to the north. Such incursions were shown to be reliant on wind-dispersal; Culicoides midge active flight on its own was not capable of achieving known rates of southern spread, nor was re-emergence of southern populations due to overwintering larvae. Data from midge trapping programmes were used to qualitatively validate the resulting simulation model.ConclusionsThe model described in this paper is intended to form the vector component of an extended model that will also include BTV transmission. A model of midge movement and population dynamics has been developed in sufficient detail such that the extended model may be used to evaluate the timing and extent of BTV outbreaks. This extended model could then be used as a platform for addressing the effectiveness of spatially targeted vaccination strategies or animal movement bans as BTV spread mitigation measures, or the impact of climate change on the risk and extent of outbreaks. These questions involving incursive Culicoides spread cannot be simply addressed with non-spatial models.

Bluetongue virus infection in naïve cattle: Identification of circulating serotypes and associated Culicoides biting midge species in Trinidad

“…Due to its close proximity to South America, Trinidad is highly susceptible to the influx of arboviruses from South America both through the movement of animals and animal products (including illegal movement), and the movement of infected vectors ( Sellers et al, 1978 , Alba et al, 2004 , Burgin et al, 2012 ). It is known that Culicoides can be passively dispersed in wind currents for up to 100km over water ( Kelso and Milne, 2014 ).…”

Simulation of the Transmission by Vectors of Bluetongue Disease and Analysis of the Control Strategy

“…Such results have been confi rmed by other authors, who performed fi eld trials [2]. Such situation has an important impact on the possible magnitude of the epizootia as well as on the planning of the preventive measures [3]. On the basis of current knowledge on BT, it is clear that global distribution of BT is constantly changing.…”

“…Data obtained by this method, were in fact hypothetic temperatures and these values were the basis of developing a sub-model that simulates vector density at a daily level, average bite rate, hatching of the vector rate, rate of Culicoida development, as well as vectors death rate. The dynamic model of the vector population has been simulated by a series of differential equations as follows: [3] where: 1. dp a -changing the number of adult vectors, during the time period dt, 2. dp i -changing the number of immature vectors, during the time period dt, 3. p a -number of mature vectors in the time interval t, 4. p i -number of immature vectors, in the time interval t, 5. p imax -maximal number of immature vectors that can be supported by the ecosystem where they replicate. 6. d i -death rate of immature vectors, 7. d a -death rate of adult vectors, 8. b -vectors laying eggs rate.…”

“…This model has been mostly developed in order to simulate BT transmission with the following vectors: Culicoides obsoletus and C. pulicarus complex since these two vector species are endemic in northern Europe and are dominant in Serbia [2]. On the other side, Culicoides immicola is the dominant vector for BT in Italy and in the Mediterranean region [3].…”

Spatial models of vector-host epidemics with directed movement of vectors over long distances

“…A variety of mathematical models of bluetongue epidemics have been developed, including stochastic event-based probabilistic models [29], [34], [47], discrete time stage structured models [49], data-based atmospheric dispersion model [1], ordinary differential equations models [13], [30], ordinary functional differential equations models [28], partial differential equations models with diffusion, but without advection [14], and partial differential equations models with diffusion and advection, but only vectors [16]. We will use the vector-host diffusion and advection terms of the model in Section 3 to focus on the spatial propagation of a bluetongue epidemic by short range and long range movement of BTV infected midges.…”