Sheep scab spatial distribution: the roles of transmission pathways

Emily J Nixon*, Ellen Brooks Pollock, Richard Wall

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

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Abstract

Background
Ovine psoroptic mange (sheep scab) is a highly pathogenic contagious infection caused by the mite Psoroptes ovis. Following 21 years in which scab was eradicated in the UK, it was inadvertently reintroduced in 1972 and, despite the implementation of a range of control methods, its prevalence increased steadily thereafter. Recent reports of resistance to macrocyclic lactone treatments may further exacerbate control problems. A better understanding of the factors that facilitate its transmission are required to allow improved management of this disease. Transmission of infection occurs within and between contiguous sheep farms via infected sheep-to-sheep or sheep–environment contact and through long-distance movements of infected sheep, such as through markets.

Methods
A stochastic metapopulation model was used to investigate the impact of different transmission routes on the spatial pattern of outbreaks. A range of model scenarios were considered following the initial infection of a cluster of highly connected contiguous farms.

Results
Scab spreads between clusters of neighbouring contiguous farms after introduction but when long-distance movements are excluded, infection then self-limits spatially at boundaries where farm connectivity is low. Inclusion of long-distance movements is required to generate the national patterns of disease spread observed.

Conclusions
Preventing the movement of scab infested sheep through sales and markets is essential for any national management programme. If effective movement control can be implemented, regional control in geographic areas where farm densities are high would allow more focussed cost-effective scab management.
Original languageEnglish
Article number344
Number of pages9
JournalParasites and Vectors
Volume14
Issue number1
Early online date29 Jun 2021
DOIs
Publication statusPublished - 29 Jun 2021

Bibliographical note

Funding Information:
This work was supported financially by the Biotechnology and Biological Sciences Research Council-funded South West Biosciences Doctoral Training Partnership (training grant reference BB/M009122/1). The funding body had no role in the design of the study, or of the collection, analysis and interpretation of the data, nor in the writing of the manuscript. EBP is supported by the National Institute for Health Research Health Protection Research Unit (NIHR HPRU) in Evaluation of Interventions at the University of Bristol and Medical Research Council grants MC/PC/19067 and MR/V038613/1.

Funding Information:
We are grateful to the Animal and Plant Health Agency (APHA) for providing sheep movement and holding data from the Animal Movement and Livestock System (AMLS) via the RADAR data warehouse.

Publisher Copyright:
© 2021, The Author(s).

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