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Published on: January 19, 2014
Sheep scab spatial distribution: the roles of transmission pathways
Emily Joanne Nixon1, Ellen Brooks-Pollock2,3, Richard Wall4
1School of Biological Sciences, University of Bristol, Bristol, BS8 1TQ, UK. emily.nixon@bristol.ac.uk.
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.
Insights
Controlling sheep scab (Psoroptes ovis) requires preventing infected sheep movement through markets. Spatial modeling shows regional control is effective in high-density farm areas when movement is restricted.
Area of Science:
- Veterinary Epidemiology
- Parasitology
- Disease Modeling
Background:
- Ovine psoroptic mange, caused by Psoroptes ovis, is a significant sheep disease re-emerging in the UK.
- Increasing resistance to treatments and understanding transmission are crucial for effective sheep scab management.
- Transmission occurs through direct contact and long-distance movement of infected sheep.
Purpose of the Study:
- To investigate the impact of different transmission routes on the spatial spread of sheep scab outbreaks.
- To inform improved management strategies for Psoroptes ovis infections.
Main Methods:
- Utilized a stochastic metapopulation model to simulate disease spread.
- Analyzed various model scenarios following initial infection in connected farm clusters.
Main Results:
- Sheep scab spreads between contiguous farms but self-limits spatially without long-distance movements.
- Long-distance sheep movements are essential to replicate observed national disease spread patterns.
- Farm connectivity influences the spatial extent of outbreaks.
Conclusions:
- Preventing the movement of scab-infested sheep via sales and markets is critical for national control programs.
- Targeted regional control in high-density farm areas can be cost-effective if movement is managed.
- Effective movement control is key to successful sheep scab management.
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