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The transmission potential of Rift Valley fever virus among livestock in the Netherlands: a modelling study.

Fischer EA, Boender GJ, Nodelijk G, de Koeijer AA, van Roermund HJ - Vet. Res. (2013)

Bottom Line: Counter-intuitively, these are the sparsely populated livestock areas, due to the high vector-host ratios in these areas.Culex pipiens s.l. is found to be the main driver of the spread and persistence, because it is by far the most abundant mosquito.Our investigation underscores the importance to determine the vector competence of this mosquito species for RVFV and its host preference.

View Article: PubMed Central - HTML - PubMed

Affiliation: Central Veterinary Institute, Part of Wageningen UR, Lelystad, The Netherlands. egil.fischer@wur.nl.

ABSTRACT
Rift Valley fever virus (RVFV) is a zoonotic vector-borne infection and causes a potentially severe disease. Many mammals are susceptible to infection including important livestock species. Although currently confined to Africa and the near-East, this disease causes concern in countries in temperate climates where both hosts and potential vectors are present, such as the Netherlands. Currently, an assessment of the probability of an outbreak occurring in this country is missing. To evaluate the transmission potential of RVFV, a mathematical model was developed and used to determine the initial growth and the Floquet ratio, which are indicators of the probability of an outbreak and of persistence in a periodic changing environment caused by seasonality. We show that several areas of the Netherlands have a high transmission potential and risk of persistence of the infection. Counter-intuitively, these are the sparsely populated livestock areas, due to the high vector-host ratios in these areas. Culex pipiens s.l. is found to be the main driver of the spread and persistence, because it is by far the most abundant mosquito. Our investigation underscores the importance to determine the vector competence of this mosquito species for RVFV and its host preference.

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Related in: MedlinePlus

Schematic flowchart of the model. The boxes (compartments) depict the variables: X = uninfected vector eggs, Y = infected vector eggs, Sv = susceptible vectors, Lv = vectors in the extrinsic incubation period, Iv = infectious vectors, Sh = susceptible hosts, Lh = latently infected hosts, Ih = infectious hosts, R = recovered and immune hosts. The solid-line arrows depict the flow out of and into compartments. Dashed line depict the influence of infectious vectors and infectious hosts on the flow from susceptible to latent infection and extrinsic incubation period. Next to the arrows are the parameters determining that flow or influence: h(t) = hatching rate at time t, b(t) = biting rate at time t, c = egg batch size, ζ = per egg vertical transmission probability, ϕv = transition rate of vector from extrinsic incubation period to infectious state, μv = mortality rate of vector, Λv = per bite transmission from one infected individual of host to a susceptible vector, Λh = the host specific per bite transmission from a vector to a host, ϕh = transition rate of host from the latent state to the infectious state, γ = recovery rate of host.
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Figure 1: Schematic flowchart of the model. The boxes (compartments) depict the variables: X = uninfected vector eggs, Y = infected vector eggs, Sv = susceptible vectors, Lv = vectors in the extrinsic incubation period, Iv = infectious vectors, Sh = susceptible hosts, Lh = latently infected hosts, Ih = infectious hosts, R = recovered and immune hosts. The solid-line arrows depict the flow out of and into compartments. Dashed line depict the influence of infectious vectors and infectious hosts on the flow from susceptible to latent infection and extrinsic incubation period. Next to the arrows are the parameters determining that flow or influence: h(t) = hatching rate at time t, b(t) = biting rate at time t, c = egg batch size, ζ = per egg vertical transmission probability, ϕv = transition rate of vector from extrinsic incubation period to infectious state, μv = mortality rate of vector, Λv = per bite transmission from one infected individual of host to a susceptible vector, Λh = the host specific per bite transmission from a vector to a host, ϕh = transition rate of host from the latent state to the infectious state, γ = recovery rate of host.

Mentions: The transmission potential of RVFV in the Netherlands is assessed using a deterministic mathematical model. Figure 1 shows the flowchart of the model. The parameters and descriptions are given in Table 1. Detailed information on the equations and model quantification is given in the Additional file 1. This model describes the local spread of the infection in a predefined small area in which all hosts and vectors mix homogeneously. In this study 5 by 5 kilometre area grids were used, based on the highest possible resolution for modelled mosquito abundances [19].


The transmission potential of Rift Valley fever virus among livestock in the Netherlands: a modelling study.

Fischer EA, Boender GJ, Nodelijk G, de Koeijer AA, van Roermund HJ - Vet. Res. (2013)

Schematic flowchart of the model. The boxes (compartments) depict the variables: X = uninfected vector eggs, Y = infected vector eggs, Sv = susceptible vectors, Lv = vectors in the extrinsic incubation period, Iv = infectious vectors, Sh = susceptible hosts, Lh = latently infected hosts, Ih = infectious hosts, R = recovered and immune hosts. The solid-line arrows depict the flow out of and into compartments. Dashed line depict the influence of infectious vectors and infectious hosts on the flow from susceptible to latent infection and extrinsic incubation period. Next to the arrows are the parameters determining that flow or influence: h(t) = hatching rate at time t, b(t) = biting rate at time t, c = egg batch size, ζ = per egg vertical transmission probability, ϕv = transition rate of vector from extrinsic incubation period to infectious state, μv = mortality rate of vector, Λv = per bite transmission from one infected individual of host to a susceptible vector, Λh = the host specific per bite transmission from a vector to a host, ϕh = transition rate of host from the latent state to the infectious state, γ = recovery rate of host.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3733972&req=5

Figure 1: Schematic flowchart of the model. The boxes (compartments) depict the variables: X = uninfected vector eggs, Y = infected vector eggs, Sv = susceptible vectors, Lv = vectors in the extrinsic incubation period, Iv = infectious vectors, Sh = susceptible hosts, Lh = latently infected hosts, Ih = infectious hosts, R = recovered and immune hosts. The solid-line arrows depict the flow out of and into compartments. Dashed line depict the influence of infectious vectors and infectious hosts on the flow from susceptible to latent infection and extrinsic incubation period. Next to the arrows are the parameters determining that flow or influence: h(t) = hatching rate at time t, b(t) = biting rate at time t, c = egg batch size, ζ = per egg vertical transmission probability, ϕv = transition rate of vector from extrinsic incubation period to infectious state, μv = mortality rate of vector, Λv = per bite transmission from one infected individual of host to a susceptible vector, Λh = the host specific per bite transmission from a vector to a host, ϕh = transition rate of host from the latent state to the infectious state, γ = recovery rate of host.
Mentions: The transmission potential of RVFV in the Netherlands is assessed using a deterministic mathematical model. Figure 1 shows the flowchart of the model. The parameters and descriptions are given in Table 1. Detailed information on the equations and model quantification is given in the Additional file 1. This model describes the local spread of the infection in a predefined small area in which all hosts and vectors mix homogeneously. In this study 5 by 5 kilometre area grids were used, based on the highest possible resolution for modelled mosquito abundances [19].

Bottom Line: Counter-intuitively, these are the sparsely populated livestock areas, due to the high vector-host ratios in these areas.Culex pipiens s.l. is found to be the main driver of the spread and persistence, because it is by far the most abundant mosquito.Our investigation underscores the importance to determine the vector competence of this mosquito species for RVFV and its host preference.

View Article: PubMed Central - HTML - PubMed

Affiliation: Central Veterinary Institute, Part of Wageningen UR, Lelystad, The Netherlands. egil.fischer@wur.nl.

ABSTRACT
Rift Valley fever virus (RVFV) is a zoonotic vector-borne infection and causes a potentially severe disease. Many mammals are susceptible to infection including important livestock species. Although currently confined to Africa and the near-East, this disease causes concern in countries in temperate climates where both hosts and potential vectors are present, such as the Netherlands. Currently, an assessment of the probability of an outbreak occurring in this country is missing. To evaluate the transmission potential of RVFV, a mathematical model was developed and used to determine the initial growth and the Floquet ratio, which are indicators of the probability of an outbreak and of persistence in a periodic changing environment caused by seasonality. We show that several areas of the Netherlands have a high transmission potential and risk of persistence of the infection. Counter-intuitively, these are the sparsely populated livestock areas, due to the high vector-host ratios in these areas. Culex pipiens s.l. is found to be the main driver of the spread and persistence, because it is by far the most abundant mosquito. Our investigation underscores the importance to determine the vector competence of this mosquito species for RVFV and its host preference.

Show MeSH
Related in: MedlinePlus