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A hierarchical network approach for modeling Rift Valley fever epidemics with applications in North America.

Xue L, Cohnstaedt LW, Scott HM, Scoglio C - PLoS ONE (2013)

Bottom Line: Spatial effects and climate factors are also addressed in the model.A surprising trend is fewer initial infectious organisms result in a longer delay before a larger and more prolonged outbreak.Cattle movement between farms is a large driver of virus expansion, thus quarantines can be efficient mitigation strategy to prevent further geographic spread.

View Article: PubMed Central - PubMed

Affiliation: Kansas State Epicenter, Department of Electrical and Computer Engineering, Kansas State University, Manhattan, Kansas, United States of America.

ABSTRACT
Rift Valley fever is a vector-borne zoonotic disease which causes high morbidity and mortality in livestock. In the event Rift Valley fever virus is introduced to the United States or other non-endemic areas, understanding the potential patterns of spread and the areas at risk based on disease vectors and hosts will be vital for developing mitigation strategies. Presented here is a general network-based mathematical model of Rift Valley fever. Given a lack of empirical data on disease vector species and their vector competence, this discrete time epidemic model uses stochastic parameters following several PERT distributions to model the dynamic interactions between hosts and likely North American mosquito vectors in dispersed geographic areas. Spatial effects and climate factors are also addressed in the model. The model is applied to a large directed asymmetric network of 3,621 nodes based on actual farms to examine a hypothetical introduction to some counties of Texas, an important ranching area in the United States of America. The nodes of the networks represent livestock farms, livestock markets, and feedlots, and the links represent cattle movements and mosquito diffusion between different nodes. Cattle and mosquito (Aedes and Culex) populations are treated with different contact networks to assess virus propagation. Rift Valley fever virus spread is assessed under various initial infection conditions (infected mosquito eggs, adults or cattle). A surprising trend is fewer initial infectious organisms result in a longer delay before a larger and more prolonged outbreak. The delay is likely caused by a lack of herd immunity while the infection expands geographically before becoming an epidemic involving many dispersed farms and animals almost simultaneously. Cattle movement between farms is a large driver of virus expansion, thus quarantines can be efficient mitigation strategy to prevent further geographic spread.

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Related in: MedlinePlus

Disease epidemic characteristics based on model output with different numbers of initially infected Culex mosquitoes on a small farm.Time to peak infection is the time until the maximal number of cases is observed and epidemic duration is the amount of time an epidemic persists.
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pone-0062049-g003: Disease epidemic characteristics based on model output with different numbers of initially infected Culex mosquitoes on a small farm.Time to peak infection is the time until the maximal number of cases is observed and epidemic duration is the amount of time an epidemic persists.

Mentions: Numerical values and definitions are in the Supporting Information. We define that if there is at least one cattle infected, then the farm is infected. represents the number of infected farms. represents the cumulative number of infected cattle throughout simulation. is the total number of infected cattle when the number of infected cattle farms is maximum. denotes the time to peak number of infected farms, that is, the time it takes from the first day to the day on which the largest number of infected farms appears as shown in Fig. 3. denotes epidemic duration, defined as the number of days with more than infected cattle farms. The average number of infected farms in each day is in the range of , the average cumulative number of infected cattle during simulation is within the range , and the average time to peak is within .


A hierarchical network approach for modeling Rift Valley fever epidemics with applications in North America.

Xue L, Cohnstaedt LW, Scott HM, Scoglio C - PLoS ONE (2013)

Disease epidemic characteristics based on model output with different numbers of initially infected Culex mosquitoes on a small farm.Time to peak infection is the time until the maximal number of cases is observed and epidemic duration is the amount of time an epidemic persists.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3646918&req=5

pone-0062049-g003: Disease epidemic characteristics based on model output with different numbers of initially infected Culex mosquitoes on a small farm.Time to peak infection is the time until the maximal number of cases is observed and epidemic duration is the amount of time an epidemic persists.
Mentions: Numerical values and definitions are in the Supporting Information. We define that if there is at least one cattle infected, then the farm is infected. represents the number of infected farms. represents the cumulative number of infected cattle throughout simulation. is the total number of infected cattle when the number of infected cattle farms is maximum. denotes the time to peak number of infected farms, that is, the time it takes from the first day to the day on which the largest number of infected farms appears as shown in Fig. 3. denotes epidemic duration, defined as the number of days with more than infected cattle farms. The average number of infected farms in each day is in the range of , the average cumulative number of infected cattle during simulation is within the range , and the average time to peak is within .

Bottom Line: Spatial effects and climate factors are also addressed in the model.A surprising trend is fewer initial infectious organisms result in a longer delay before a larger and more prolonged outbreak.Cattle movement between farms is a large driver of virus expansion, thus quarantines can be efficient mitigation strategy to prevent further geographic spread.

View Article: PubMed Central - PubMed

Affiliation: Kansas State Epicenter, Department of Electrical and Computer Engineering, Kansas State University, Manhattan, Kansas, United States of America.

ABSTRACT
Rift Valley fever is a vector-borne zoonotic disease which causes high morbidity and mortality in livestock. In the event Rift Valley fever virus is introduced to the United States or other non-endemic areas, understanding the potential patterns of spread and the areas at risk based on disease vectors and hosts will be vital for developing mitigation strategies. Presented here is a general network-based mathematical model of Rift Valley fever. Given a lack of empirical data on disease vector species and their vector competence, this discrete time epidemic model uses stochastic parameters following several PERT distributions to model the dynamic interactions between hosts and likely North American mosquito vectors in dispersed geographic areas. Spatial effects and climate factors are also addressed in the model. The model is applied to a large directed asymmetric network of 3,621 nodes based on actual farms to examine a hypothetical introduction to some counties of Texas, an important ranching area in the United States of America. The nodes of the networks represent livestock farms, livestock markets, and feedlots, and the links represent cattle movements and mosquito diffusion between different nodes. Cattle and mosquito (Aedes and Culex) populations are treated with different contact networks to assess virus propagation. Rift Valley fever virus spread is assessed under various initial infection conditions (infected mosquito eggs, adults or cattle). A surprising trend is fewer initial infectious organisms result in a longer delay before a larger and more prolonged outbreak. The delay is likely caused by a lack of herd immunity while the infection expands geographically before becoming an epidemic involving many dispersed farms and animals almost simultaneously. Cattle movement between farms is a large driver of virus expansion, thus quarantines can be efficient mitigation strategy to prevent further geographic spread.

Show MeSH
Related in: MedlinePlus