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A new algorithm quantifies the roles of wind and midge flight activity in the bluetongue epizootic in northwest Europe

A new algorithm quantifies the roles of wind and midge flight activity in the bluetongue epizootic in northwest Europe
A new algorithm quantifies the roles of wind and midge flight activity in the bluetongue epizootic in northwest Europe
The 2006 bluetongue (BT) outbreak in northwestern Europe had devastating effects on cattle and sheep in that intensively farmed area. The role of wind in disease spread, through its effect on Culicoides dispersal, is still uncertain, and remains unquantified. We examine here the relationship between farm-level infection dates and wind speed and direction within the framework of a novel model involving both mechanistic and stochastic steps. We consider wind as both a carrier of host semio-chemicals, to which midges might respond by upwind flight, and as a transporter of the midges themselves, in a more or less downwind direction. For completeness, we also consider midge movement independent of wind and various combinations of upwind, downwind and random movements. Using stochastic simulation, we are able to explain infection onset at 94 per cent of the 2025 affected farms. We conclude that 54 per cent of outbreaks occurred through (presumably midge) movement of infections over distances of no more than 5 km, 92 per cent over distances of no more than 31 km and only 2 per cent over any greater distances. The modal value for all infections combined is less than 1 km. Our analysis suggests that previous claims for a higher frequency of long-distance infections are unfounded. We suggest that many apparent long-distance infections resulted from sequences of shorter-range infections; a 'stepping stone' effect. Our analysis also found that downwind movement (the only sort so far considered in explanations of BT epidemics) is responsible for only 39 per cent of all infections, and highlights the effective contribution to disease spread of upwind midge movement, which accounted for 38 per cent of all infections. The importance of midge flight speed is also investigated. Within the same model framework, lower midge active flight speed (of 0.13 rather than 0.5 m s(-1)) reduced virtually to zero the role of upwind movement, mainly because modelled wind speeds in the area concerned were usually greater than such flight speed. Our analysis, therefore, highlights the need to improve our knowledge of midge flight speed in field situations, which is still very poorly understood. Finally, the model returned an intrinsic incubation period of 8 days, in accordance with the values reported in the literature. We argue that better understanding of the movement of infected insect vectors is an important ingredient in the management of future outbreaks of BT in Europe, and other devastating vector-borne diseases elsewhere.
bluetongue culicoides flight wind fields mechanistic and stochastic simulation disease spread culicoides biting midges brevitarsis kieffer diptera virus serotype 8 western-europe northern europe trajectory analysis local dispersal united-kingdom 2006 epidemic air streams
1471-2954
2354-2362
Sedda, L.
ae6a74e0-ff67-4678-aefc-9976179294f6
Brown, H. E.
8839128c-c6d7-4af2-96b6-c12ea9b94442
Purse, B. V.
d403efa0-e1ba-4a78-9e8a-bd8afe6623d0
Burgin, L.
380edf82-48f0-4654-9466-03a79e139db0
Gloster, J.
d1c9ffcc-dcf1-4e85-9acb-5e305c34ee55
Rogers, D. J.
658f04d4-bdb9-4ab2-bebb-539a94f85e99
Sedda, L.
ae6a74e0-ff67-4678-aefc-9976179294f6
Brown, H. E.
8839128c-c6d7-4af2-96b6-c12ea9b94442
Purse, B. V.
d403efa0-e1ba-4a78-9e8a-bd8afe6623d0
Burgin, L.
380edf82-48f0-4654-9466-03a79e139db0
Gloster, J.
d1c9ffcc-dcf1-4e85-9acb-5e305c34ee55
Rogers, D. J.
658f04d4-bdb9-4ab2-bebb-539a94f85e99

Sedda, L., Brown, H. E., Purse, B. V., Burgin, L., Gloster, J. and Rogers, D. J. (2012) A new algorithm quantifies the roles of wind and midge flight activity in the bluetongue epizootic in northwest Europe. Proceedings of the Royal Society B: Biological Sciences, 279 (1737), 2354-2362. (doi:10.1098/rspb.2011.2555).

Record type: Article

Abstract

The 2006 bluetongue (BT) outbreak in northwestern Europe had devastating effects on cattle and sheep in that intensively farmed area. The role of wind in disease spread, through its effect on Culicoides dispersal, is still uncertain, and remains unquantified. We examine here the relationship between farm-level infection dates and wind speed and direction within the framework of a novel model involving both mechanistic and stochastic steps. We consider wind as both a carrier of host semio-chemicals, to which midges might respond by upwind flight, and as a transporter of the midges themselves, in a more or less downwind direction. For completeness, we also consider midge movement independent of wind and various combinations of upwind, downwind and random movements. Using stochastic simulation, we are able to explain infection onset at 94 per cent of the 2025 affected farms. We conclude that 54 per cent of outbreaks occurred through (presumably midge) movement of infections over distances of no more than 5 km, 92 per cent over distances of no more than 31 km and only 2 per cent over any greater distances. The modal value for all infections combined is less than 1 km. Our analysis suggests that previous claims for a higher frequency of long-distance infections are unfounded. We suggest that many apparent long-distance infections resulted from sequences of shorter-range infections; a 'stepping stone' effect. Our analysis also found that downwind movement (the only sort so far considered in explanations of BT epidemics) is responsible for only 39 per cent of all infections, and highlights the effective contribution to disease spread of upwind midge movement, which accounted for 38 per cent of all infections. The importance of midge flight speed is also investigated. Within the same model framework, lower midge active flight speed (of 0.13 rather than 0.5 m s(-1)) reduced virtually to zero the role of upwind movement, mainly because modelled wind speeds in the area concerned were usually greater than such flight speed. Our analysis, therefore, highlights the need to improve our knowledge of midge flight speed in field situations, which is still very poorly understood. Finally, the model returned an intrinsic incubation period of 8 days, in accordance with the values reported in the literature. We argue that better understanding of the movement of infected insect vectors is an important ingredient in the management of future outbreaks of BT in Europe, and other devastating vector-borne diseases elsewhere.

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More information

Published date: 2012
Additional Information: 940KN Times Cited:15 Cited References Count:48
Keywords: bluetongue culicoides flight wind fields mechanistic and stochastic simulation disease spread culicoides biting midges brevitarsis kieffer diptera virus serotype 8 western-europe northern europe trajectory analysis local dispersal united-kingdom 2006 epidemic air streams
Organisations: Global Env Change & Earth Observation

Identifiers

Local EPrints ID: 361774
URI: http://eprints.soton.ac.uk/id/eprint/361774
ISSN: 1471-2954
PURE UUID: 46407c77-1dfd-4520-ae34-d092e32b9284

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Date deposited: 12 Feb 2014 12:44
Last modified: 14 Mar 2024 15:56

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Contributors

Author: L. Sedda
Author: H. E. Brown
Author: B. V. Purse
Author: L. Burgin
Author: J. Gloster
Author: D. J. Rogers

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