Sheep scab spatial distribution: the roles of transmission pathways

Emily Joanne Nixon,Ellen Brooks-Pollock,Richard Wall

doi:10.1186/s13071-021-04850-y

Emily Joanne Nixon, Ellen Brooks-Pollock + Show 1 more

Open Access

https://doi.org/10.1186/s13071-021-04850-y

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Abstract

BackgroundOvine 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.MethodsA 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.ResultsScab 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.ConclusionsPreventing 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.Graphical

Highlights

IntroductionOvine psoroptic mange (sheep scab) is a highly pathogenic contagious infection caused by the mite Psoroptes ovis
Ovine psoroptic mange is a highly pathogenic contagious infection caused by the mite Psoroptes ovis
Model description A stochastic networked metapopulation model for sheep scab [29] was used for the simulations described

Summary

Introduction

Ovine psoroptic mange (sheep scab) is a highly pathogenic contagious infection caused by the mite Psoroptes ovis. Ovine psoroptic mange (sheep scab) is the result of a hypersensitivity response to the faecal material of the parasitic mite, Psoroptes ovis [1] This highly pathogenic and infectious ectoparasitic condition impacts sheep husbandry systems in many parts of the world [2]. Economic losses resulting from scab are due to pruritus and excoriation, leading to wool loss [9], weight loss [10], reproductive losses [11] and, the mortality of infested hosts [12] These losses, along with the associated costs of treatment, food and labour, are estimated to cost the sheep industry in the UK approximately GBP 78–202 million per year [13]. Sheep scab represents a significant economic and animal welfare issue

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