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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

Effect of non-livestock hosts on the Floquet ratio RT for a sparsely populated livestock area. The RT was calculated for an area with livestock density of 200 animals per 5 × 5 km and on the x-axis the number of additional hosts per livestock host. Additional hosts were either refractory (i.e. birds), susceptible with shorter infectious period (i.e. rodents), or susceptible and equal to livestock characteristics.
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Figure 7: Effect of non-livestock hosts on the Floquet ratio RT for a sparsely populated livestock area. The RT was calculated for an area with livestock density of 200 animals per 5 × 5 km and on the x-axis the number of additional hosts per livestock host. Additional hosts were either refractory (i.e. birds), susceptible with shorter infectious period (i.e. rodents), or susceptible and equal to livestock characteristics.

Mentions: When the vectors are biting on animals other than livestock, the RT is lower than without additional hosts. If these animals are refractory, i.e. resistant to infection, the RT is lower than when these animals also contribute to the transmission of RVFV. For our sparsely populated livestock area (Table 2) the RT crosses the threshold when the number of refractory hosts is 0.65 times the number of livestock animals, while this occurs if the number of rodent hosts exceeds 3.48 times the number of livestock animals. If the number of livestock (or animals which have epidemiological equal properties) increases by 7.39 times the threshold is crossed as well (Figure 7).


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)

Effect of non-livestock hosts on the Floquet ratio RT for a sparsely populated livestock area. The RT was calculated for an area with livestock density of 200 animals per 5 × 5 km and on the x-axis the number of additional hosts per livestock host. Additional hosts were either refractory (i.e. birds), susceptible with shorter infectious period (i.e. rodents), or susceptible and equal to livestock characteristics.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 7: Effect of non-livestock hosts on the Floquet ratio RT for a sparsely populated livestock area. The RT was calculated for an area with livestock density of 200 animals per 5 × 5 km and on the x-axis the number of additional hosts per livestock host. Additional hosts were either refractory (i.e. birds), susceptible with shorter infectious period (i.e. rodents), or susceptible and equal to livestock characteristics.
Mentions: When the vectors are biting on animals other than livestock, the RT is lower than without additional hosts. If these animals are refractory, i.e. resistant to infection, the RT is lower than when these animals also contribute to the transmission of RVFV. For our sparsely populated livestock area (Table 2) the RT crosses the threshold when the number of refractory hosts is 0.65 times the number of livestock animals, while this occurs if the number of rodent hosts exceeds 3.48 times the number of livestock animals. If the number of livestock (or animals which have epidemiological equal properties) increases by 7.39 times the threshold is crossed as well (Figure 7).

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