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A Stochastic Model to Study Rift Valley Fever Persistence with Different Seasonal Patterns of Vector Abundance: New Insights on the Endemicity in the Tropical Island of Mayotte.

Cavalerie L, Charron MV, Ezanno P, Dommergues L, Zumbo B, Cardinale E - PLoS ONE (2015)

Bottom Line: Transmission rates had to be divided by more than five to best fit observed data.Five years after introduction, RVF persisted in more than 10% of the simulations, even under this scenario of low transmission.Hence, active surveillance must be maintained to better understand the risk related to RVF persistence and to prevent new introductions.

View Article: PubMed Central - PubMed

Affiliation: CRVOI, Centre de Recherche et de Veille sur les maladies émergentes dans l'Océan Indien, F-97490 Sainte Clotilde, La Réunion, France; CIRAD, UMR CMAEE, F-97490, Sainte Clotilde, France; INRA, UMR 1309 CMAEE, F-34398, Montpellier, France; AgroParisTech, F-75005, Paris, France; Université de la Réunion, F-97715 Saint Denis, La Réunion, France.

ABSTRACT
Rift Valley fever (RVF) is a zoonotic vector-borne disease causing abortion storms in cattle and human epidemics in Africa. Our aim was to evaluate RVF persistence in a seasonal and isolated population and to apply it to Mayotte Island (Indian Ocean), where the virus was still silently circulating four years after its last known introduction in 2007. We proposed a stochastic model to estimate RVF persistence over several years and under four seasonal patterns of vector abundance. Firstly, the model predicted a wide range of virus spread patterns, from obligate persistence in a constant or tropical environment (without needing vertical transmission or reintroduction) to frequent extinctions in a drier climate. We then identified for each scenario of seasonality the parameters that most influenced prediction variations. Persistence was sensitive to vector lifespan and biting rate in a tropical climate, and to host viraemia duration and vector lifespan in a drier climate. The first epizootic peak was primarily sensitive to viraemia duration and thus likely to be controlled by vaccination, whereas subsequent peaks were sensitive to vector lifespan and biting rate in a tropical climate, and to host birth rate and viraemia duration in arid climates. Finally, we parameterized the model according to Mayotte known environment. Mosquito captures estimated the abundance of eight potential RVF vectors. Review of RVF competence studies on these species allowed adjusting transmission probabilities per bite. Ruminant serological data since 2004 and three new cross-sectional seroprevalence studies are presented. Transmission rates had to be divided by more than five to best fit observed data. Five years after introduction, RVF persisted in more than 10% of the simulations, even under this scenario of low transmission. Hence, active surveillance must be maintained to better understand the risk related to RVF persistence and to prevent new introductions.

No MeSH data available.


Related in: MedlinePlus

RVF dynamics for different vector emergence scenarios.The 1st column shows the distribution of hosts for each health state: susceptible (SH) in green, infectious (IH) in red and recovered (RH) in blue, for 1500 model repetitions. The 2nd column shows the infectious vectors. The 3rd column shows the probability of virus persistence. Each line corresponds to a scenario (Fig 2).
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pone.0130838.g003: RVF dynamics for different vector emergence scenarios.The 1st column shows the distribution of hosts for each health state: susceptible (SH) in green, infectious (IH) in red and recovered (RH) in blue, for 1500 model repetitions. The 2nd column shows the infectious vectors. The 3rd column shows the probability of virus persistence. Each line corresponds to a scenario (Fig 2).

Mentions: Search engines were used to find publications on PubMed (http://www.ncbi.nlm.nih.gov/) and ScienceDirect (http://www.sciencedirect.com/) using key words “Rift Valley fever” AND “Mayotte” in English and French. Thirty-two publications were found. Local veterinary services and research institutions were interviewed to find seroprevalence data in unpublished documents, reports or databases. Original datasets were obtained upon request to the authors in order to specify temporal frames and to calculate confidence intervals when necessary.From May 2012 to April 2013, ruminants were selected to obtain a representative sample of the ruminant population of Mayotte. We divided Mayotte into five zones to cover each agro-ecosystem (Fig 3). The 30 farms included in the study were randomly selected from the most comprehensive database available in Mayotte from the Chambre de l’Agriculture, de la Pêche et de l’Aquaculture de Mayotte (CAPAM, a local public agricultural institution). All ruminants older than six months of age for cattle and three months of age for small ruminants (beyond colostral immunity) belonging to the same owner were eligible for inclusion in the study.


A Stochastic Model to Study Rift Valley Fever Persistence with Different Seasonal Patterns of Vector Abundance: New Insights on the Endemicity in the Tropical Island of Mayotte.

Cavalerie L, Charron MV, Ezanno P, Dommergues L, Zumbo B, Cardinale E - PLoS ONE (2015)

RVF dynamics for different vector emergence scenarios.The 1st column shows the distribution of hosts for each health state: susceptible (SH) in green, infectious (IH) in red and recovered (RH) in blue, for 1500 model repetitions. The 2nd column shows the infectious vectors. The 3rd column shows the probability of virus persistence. Each line corresponds to a scenario (Fig 2).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493030&req=5

pone.0130838.g003: RVF dynamics for different vector emergence scenarios.The 1st column shows the distribution of hosts for each health state: susceptible (SH) in green, infectious (IH) in red and recovered (RH) in blue, for 1500 model repetitions. The 2nd column shows the infectious vectors. The 3rd column shows the probability of virus persistence. Each line corresponds to a scenario (Fig 2).
Mentions: Search engines were used to find publications on PubMed (http://www.ncbi.nlm.nih.gov/) and ScienceDirect (http://www.sciencedirect.com/) using key words “Rift Valley fever” AND “Mayotte” in English and French. Thirty-two publications were found. Local veterinary services and research institutions were interviewed to find seroprevalence data in unpublished documents, reports or databases. Original datasets were obtained upon request to the authors in order to specify temporal frames and to calculate confidence intervals when necessary.From May 2012 to April 2013, ruminants were selected to obtain a representative sample of the ruminant population of Mayotte. We divided Mayotte into five zones to cover each agro-ecosystem (Fig 3). The 30 farms included in the study were randomly selected from the most comprehensive database available in Mayotte from the Chambre de l’Agriculture, de la Pêche et de l’Aquaculture de Mayotte (CAPAM, a local public agricultural institution). All ruminants older than six months of age for cattle and three months of age for small ruminants (beyond colostral immunity) belonging to the same owner were eligible for inclusion in the study.

Bottom Line: Transmission rates had to be divided by more than five to best fit observed data.Five years after introduction, RVF persisted in more than 10% of the simulations, even under this scenario of low transmission.Hence, active surveillance must be maintained to better understand the risk related to RVF persistence and to prevent new introductions.

View Article: PubMed Central - PubMed

Affiliation: CRVOI, Centre de Recherche et de Veille sur les maladies émergentes dans l'Océan Indien, F-97490 Sainte Clotilde, La Réunion, France; CIRAD, UMR CMAEE, F-97490, Sainte Clotilde, France; INRA, UMR 1309 CMAEE, F-34398, Montpellier, France; AgroParisTech, F-75005, Paris, France; Université de la Réunion, F-97715 Saint Denis, La Réunion, France.

ABSTRACT
Rift Valley fever (RVF) is a zoonotic vector-borne disease causing abortion storms in cattle and human epidemics in Africa. Our aim was to evaluate RVF persistence in a seasonal and isolated population and to apply it to Mayotte Island (Indian Ocean), where the virus was still silently circulating four years after its last known introduction in 2007. We proposed a stochastic model to estimate RVF persistence over several years and under four seasonal patterns of vector abundance. Firstly, the model predicted a wide range of virus spread patterns, from obligate persistence in a constant or tropical environment (without needing vertical transmission or reintroduction) to frequent extinctions in a drier climate. We then identified for each scenario of seasonality the parameters that most influenced prediction variations. Persistence was sensitive to vector lifespan and biting rate in a tropical climate, and to host viraemia duration and vector lifespan in a drier climate. The first epizootic peak was primarily sensitive to viraemia duration and thus likely to be controlled by vaccination, whereas subsequent peaks were sensitive to vector lifespan and biting rate in a tropical climate, and to host birth rate and viraemia duration in arid climates. Finally, we parameterized the model according to Mayotte known environment. Mosquito captures estimated the abundance of eight potential RVF vectors. Review of RVF competence studies on these species allowed adjusting transmission probabilities per bite. Ruminant serological data since 2004 and three new cross-sectional seroprevalence studies are presented. Transmission rates had to be divided by more than five to best fit observed data. Five years after introduction, RVF persisted in more than 10% of the simulations, even under this scenario of low transmission. Hence, active surveillance must be maintained to better understand the risk related to RVF persistence and to prevent new introductions.

No MeSH data available.


Related in: MedlinePlus