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Human mobility and the worldwide impact of intentional localized highly pathogenic virus release.

Gonçalves B, Balcan D, Vespignani A - Sci Rep (2013)

Bottom Line: However, such studies do not consider the effects of human mobility patterns.These results have two major implications: i) intentional release of a highly pathogenic agent within a country will have global effects; ii) the release event may trigger outbreaks in countries lacking the health infrastructure necessary for effective containment.The presented study provides data with potential uses in defining contingency plans at the National and International level.

View Article: PubMed Central - PubMed

Affiliation: Aix-Marseille Université, CNRS, CPT, UMR 7332, 13288 Marseille, France.

ABSTRACT
The threat of bioterrorism and the possibility of accidental release have spawned a growth of interest in modeling the course of the release of a highly pathogenic agent. Studies focused on strategies to contain local outbreaks after their detection show that timely interventions with vaccination and contact tracing are able to halt transmission. However, such studies do not consider the effects of human mobility patterns. Using a large-scale structured metapopulation model to simulate the global spread of smallpox after an intentional release event, we show that index cases and potential outbreaks can occur in different continents even before the detection of the pathogen release. These results have two major implications: i) intentional release of a highly pathogenic agent within a country will have global effects; ii) the release event may trigger outbreaks in countries lacking the health infrastructure necessary for effective containment. The presented study provides data with potential uses in defining contingency plans at the National and International level.

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Related in: MedlinePlus

Timeline of international smallpox spread.Top) Intentional spread by five individuals avoiding detection and medical care. Bottom) Virus release with the exposure of 10 civilians. (A–B) Probability of observing an international outbreak (presence of cases outside the initial target country) at the time of initial detection and the following three weeks. (C–D) Number of affected countries conditional to the international outbreak. (E–F) Number of cases outside the target country conditional to global outbreak. Boxplots display the median, 50% and 95% reference ranges from 5,000 simulated events with the baseline parameters of Table 1.
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f2: Timeline of international smallpox spread.Top) Intentional spread by five individuals avoiding detection and medical care. Bottom) Virus release with the exposure of 10 civilians. (A–B) Probability of observing an international outbreak (presence of cases outside the initial target country) at the time of initial detection and the following three weeks. (C–D) Number of affected countries conditional to the international outbreak. (E–F) Number of cases outside the target country conditional to global outbreak. Boxplots display the median, 50% and 95% reference ranges from 5,000 simulated events with the baseline parameters of Table 1.

Mentions: In Fig. 2 we report the number of countries affected and the smallpox cases observed outside the targeted country for the baseline transmission rate and for different delays after the initial outbreak detection. It is possible to observe that even at the moment of detection of the small-scale outbreak, with R0 = 5, the 50% reference range indicates that 2 to 4 countries have already imported at least one exposed individual. This is also observed with the number of exposed individuals dispersed in countries outside the target. The risk analysis for each country is composed of two components: the probability that a country will have at least one infected individual and the expected number of infected cases conditional to this event. In order to provide a global visualization of the risk worldwide, we provide risk maps at the level of single census area. In Fig. 3 we show a worldwide map that shows the probability of observing exposed individuals at the detection and after two weeks from detection of the release at the scale of the census area used in the numerical simulation. The statistics are obtained by analyzing 5,000 different stochastic realizations of the smallpox release with the same initial conditions. It is also important to stress that the reported outbreak probabilities refer to initial seeding events and small-scale outbreaks that may or may not lead to large-scale epidemics depending on local containment policies. In each different realization however the number of cases is generally localized in specific census areas. For instance if we consider Germany, we might observe a realization with 3 cases in Frankfurt, while in a different realization we may have 4 cases in Munich.


Human mobility and the worldwide impact of intentional localized highly pathogenic virus release.

Gonçalves B, Balcan D, Vespignani A - Sci Rep (2013)

Timeline of international smallpox spread.Top) Intentional spread by five individuals avoiding detection and medical care. Bottom) Virus release with the exposure of 10 civilians. (A–B) Probability of observing an international outbreak (presence of cases outside the initial target country) at the time of initial detection and the following three weeks. (C–D) Number of affected countries conditional to the international outbreak. (E–F) Number of cases outside the target country conditional to global outbreak. Boxplots display the median, 50% and 95% reference ranges from 5,000 simulated events with the baseline parameters of Table 1.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3713588&req=5

f2: Timeline of international smallpox spread.Top) Intentional spread by five individuals avoiding detection and medical care. Bottom) Virus release with the exposure of 10 civilians. (A–B) Probability of observing an international outbreak (presence of cases outside the initial target country) at the time of initial detection and the following three weeks. (C–D) Number of affected countries conditional to the international outbreak. (E–F) Number of cases outside the target country conditional to global outbreak. Boxplots display the median, 50% and 95% reference ranges from 5,000 simulated events with the baseline parameters of Table 1.
Mentions: In Fig. 2 we report the number of countries affected and the smallpox cases observed outside the targeted country for the baseline transmission rate and for different delays after the initial outbreak detection. It is possible to observe that even at the moment of detection of the small-scale outbreak, with R0 = 5, the 50% reference range indicates that 2 to 4 countries have already imported at least one exposed individual. This is also observed with the number of exposed individuals dispersed in countries outside the target. The risk analysis for each country is composed of two components: the probability that a country will have at least one infected individual and the expected number of infected cases conditional to this event. In order to provide a global visualization of the risk worldwide, we provide risk maps at the level of single census area. In Fig. 3 we show a worldwide map that shows the probability of observing exposed individuals at the detection and after two weeks from detection of the release at the scale of the census area used in the numerical simulation. The statistics are obtained by analyzing 5,000 different stochastic realizations of the smallpox release with the same initial conditions. It is also important to stress that the reported outbreak probabilities refer to initial seeding events and small-scale outbreaks that may or may not lead to large-scale epidemics depending on local containment policies. In each different realization however the number of cases is generally localized in specific census areas. For instance if we consider Germany, we might observe a realization with 3 cases in Frankfurt, while in a different realization we may have 4 cases in Munich.

Bottom Line: However, such studies do not consider the effects of human mobility patterns.These results have two major implications: i) intentional release of a highly pathogenic agent within a country will have global effects; ii) the release event may trigger outbreaks in countries lacking the health infrastructure necessary for effective containment.The presented study provides data with potential uses in defining contingency plans at the National and International level.

View Article: PubMed Central - PubMed

Affiliation: Aix-Marseille Université, CNRS, CPT, UMR 7332, 13288 Marseille, France.

ABSTRACT
The threat of bioterrorism and the possibility of accidental release have spawned a growth of interest in modeling the course of the release of a highly pathogenic agent. Studies focused on strategies to contain local outbreaks after their detection show that timely interventions with vaccination and contact tracing are able to halt transmission. However, such studies do not consider the effects of human mobility patterns. Using a large-scale structured metapopulation model to simulate the global spread of smallpox after an intentional release event, we show that index cases and potential outbreaks can occur in different continents even before the detection of the pathogen release. These results have two major implications: i) intentional release of a highly pathogenic agent within a country will have global effects; ii) the release event may trigger outbreaks in countries lacking the health infrastructure necessary for effective containment. The presented study provides data with potential uses in defining contingency plans at the National and International level.

Show MeSH
Related in: MedlinePlus