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Sheep scab outbreaks in Great Britain between 1973 and 1992: spatial and temporal patterns
N P French1, E Berriatua, R Wall
1Department of Veterinary Clinical Science & Animal Husbandry, University of Liverpool, Leahurst, Neston, UK. n.p.french@liv.ac.uk
Veterinary Parasitology
|July 28, 1999
Summary
Sheep scab outbreaks, caused by the mange mite Psoroptes ovis, show seasonal patterns and local spread. Control policy changes influenced outbreak frequency and seasonality over 20 years.
Area of Science:
- Veterinary Epidemiology
- Parasitology
- Spatial Analysis
Background:
- Sheep scab, caused by the mange mite Psoroptes ovis, re-emerged in the UK in 1973 after a 20-year eradication period.
- From 1973 to 1992, 1480 flock outbreaks were reported, with control measures deregulated in June 1992.
Purpose of the Study:
- To analyze the spatial and temporal patterns of sheep scab outbreaks.
- To investigate the influence of control policies and seasonal factors on outbreak dynamics.
Main Methods:
- Time series analysis to identify seasonal and long-term trends.
- Geographical Information System (GIS) for spatial pattern analysis.
- Space-time interaction analysis (K-function) to detect clustering and spread.
Main Results:
- Significant seasonal cyclicity observed, with peak outbreaks in winter months.
- A shift in seasonality towards autumn months noted after the removal of compulsory summer dipping in 1988.
- Evidence of an 8-year cyclical pattern correlating with national control policy changes.
- Strong evidence of space-time clustering (p < 0.001) and local spread (< 12 km within 5 months).
Conclusions:
- Sheep scab outbreaks exhibit complex spatial and temporal dynamics influenced by seasonality and control policies.
- Local transmission is a significant factor in the spread of sheep scab.
- Policy interventions and changes in dipping practices demonstrably impact disease patterns.