Pruritus is a common feature in sheep infected with the BSE agent

Timm Konold¹^,2 , Gemma Bone¹ , Alberto Vidal-Diez¹ , Raul Tortosa³ , Andrew Davis⁴ , Glenda Dexter¹ , Peter Hill⁵ , Martin Jeffrey⁶ , Marion M Simmons¹ , Melanie J Chaplin¹ , Susan J Bellworthy¹ and Christine Berthelin-Baker⁷

¹Veterinary Laboratories Agency Weybridge, Woodham Lane, Addlestone, UK

²Royal Veterinary College, Population Biology and Disease Control Research Group, North Mymms, Hatfield, UK

³Department of Animal Medicine and Surgery, Institute of Neuroscience, Veterinary Faculty, Universitat Autònoma de Barcelona, Barcelona, Spain

⁴Pathology, Infectious Disease & Biosecurity, School of Veterinary Science, University of Queensland, Brisbane, Australia

⁵ADAS Drayton, Alcester Road, Stratford upon Avon, UK

⁶Veterinary Laboratories Agency Lasswade, Pentlands Science Park, Bush Loan, Penicuik, UK

⁷All Animals Neurology & Neurosurgery, Atlanta, Georgia, USA

author email corresponding author email

BMC Veterinary Research 2008, 4:16doi:10.1186/1746-6148-4-16


Published:	29 April 2008

Abstract

Background

The variability in the clinical or pathological presentation of transmissible spongiform encephalopathies (TSEs) in sheep, such as scrapie and bovine spongiform encephalopathy (BSE), has been attributed to prion protein genotype, strain, breed, clinical duration, dose, route and type of inoculum and the age at infection. The study aimed to describe the clinical signs in sheep infected with the BSE agent throughout its clinical course to determine whether the clinical signs were as variable as described for classical scrapie in sheep. The clinical signs were compared to BSE-negative sheep to assess if disease-specific clinical markers exist.

Results

Forty-seven (34%) of 139 sheep, which comprised 123 challenged sheep and 16 undosed controls, were positive for BSE. Affected sheep belonged to five different breeds and three different genotypes (ARQ/ARQ, VRQ/VRQ and AHQ/AHQ). None of the controls or BSE exposed sheep with ARR alleles were positive. Pruritus was present in 41 (87%) BSE positive sheep; the remaining six were judged to be pre-clinically infected. Testing of the response to scratching along the dorsum of a sheep proved to be a good indicator of clinical disease with a test sensitivity of 85% and specificity of 98% and usually coincided with weight loss. Clinical signs that were displayed significantly earlier in BSE positive cases compared to negative cases were behavioural changes, pruritic behaviour, a positive scratch test, alopecia, skin lesions, teeth grinding, tremor, ataxia, loss of weight and loss of body condition. The frequency and severity of each specific clinical sign usually increased with the progression of disease over a period of 16–20 weeks.

Conclusion

Our results suggest that BSE in sheep presents with relatively uniform clinical signs, with pruritus of increased severity and abnormalities in behaviour or movement as the disease progressed. Based on the studied sheep, these clinical features appear to be independent of breed, affected genotype, dose, route of inoculation and whether BSE was passed into sheep from cattle or from other sheep, suggesting that the clinical phenotype of BSE is influenced by the TSE strain more than by other factors. The clinical phenotype of BSE in the genotypes and breed studied was indistinguishable from that described for classical scrapie cases.