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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

Predicted persistence and host infection dynamics with low transmission rates and observed seroprevalence in Mayotte.(A) Persistence predicted by the model with parameters found in Table 2 and a lower set of transmission rates (cHV = 0.09, cVH = 0.04, k = 0.6). (B) Host infection dynamics predicted by the model with parameters found in Table 2 and a lower set of transmission rates (cHV = 0.09, cVH = 0.04, k = 0.6). Susceptible hosts (SH) are in green, infectious (IH) in red and recovered (RH) in blue. (C) Observed seroprevalence in ruminants in Mayotte from 2004 to 2013 is in purple. Seroprevalence predicted by the model, from 2007 on, is in blue. Blue dots represent the median and arrows the 5 and 95% percentiles of the 1500 repetitions.
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pone.0130838.g007: Predicted persistence and host infection dynamics with low transmission rates and observed seroprevalence in Mayotte.(A) Persistence predicted by the model with parameters found in Table 2 and a lower set of transmission rates (cHV = 0.09, cVH = 0.04, k = 0.6). (B) Host infection dynamics predicted by the model with parameters found in Table 2 and a lower set of transmission rates (cHV = 0.09, cVH = 0.04, k = 0.6). Susceptible hosts (SH) are in green, infectious (IH) in red and recovered (RH) in blue. (C) Observed seroprevalence in ruminants in Mayotte from 2004 to 2013 is in purple. Seroprevalence predicted by the model, from 2007 on, is in blue. Blue dots represent the median and arrows the 5 and 95% percentiles of the 1500 repetitions.

Mentions: In the serological survey of 2012–2013, we found 30, 33, and 29 positive animals out of 131, 157, and 161, respectively. Using all available knowledge (literature [7,10], an internal report of 2009 and the 2012–2013 serological survey), the seroprevalence observed between 2004 and 2013 ranged from 3% to 35%. At virus introduction, remaining seroprevalence was set to 16.2% as found in the raw data of the study from Cêtre [7] (Fig 7C and Table 3).


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)

Predicted persistence and host infection dynamics with low transmission rates and observed seroprevalence in Mayotte.(A) Persistence predicted by the model with parameters found in Table 2 and a lower set of transmission rates (cHV = 0.09, cVH = 0.04, k = 0.6). (B) Host infection dynamics predicted by the model with parameters found in Table 2 and a lower set of transmission rates (cHV = 0.09, cVH = 0.04, k = 0.6). Susceptible hosts (SH) are in green, infectious (IH) in red and recovered (RH) in blue. (C) Observed seroprevalence in ruminants in Mayotte from 2004 to 2013 is in purple. Seroprevalence predicted by the model, from 2007 on, is in blue. Blue dots represent the median and arrows the 5 and 95% percentiles of the 1500 repetitions.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0130838.g007: Predicted persistence and host infection dynamics with low transmission rates and observed seroprevalence in Mayotte.(A) Persistence predicted by the model with parameters found in Table 2 and a lower set of transmission rates (cHV = 0.09, cVH = 0.04, k = 0.6). (B) Host infection dynamics predicted by the model with parameters found in Table 2 and a lower set of transmission rates (cHV = 0.09, cVH = 0.04, k = 0.6). Susceptible hosts (SH) are in green, infectious (IH) in red and recovered (RH) in blue. (C) Observed seroprevalence in ruminants in Mayotte from 2004 to 2013 is in purple. Seroprevalence predicted by the model, from 2007 on, is in blue. Blue dots represent the median and arrows the 5 and 95% percentiles of the 1500 repetitions.
Mentions: In the serological survey of 2012–2013, we found 30, 33, and 29 positive animals out of 131, 157, and 161, respectively. Using all available knowledge (literature [7,10], an internal report of 2009 and the 2012–2013 serological survey), the seroprevalence observed between 2004 and 2013 ranged from 3% to 35%. At virus introduction, remaining seroprevalence was set to 16.2% as found in the raw data of the study from Cêtre [7] (Fig 7C and Table 3).

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