Two major ruminant acute phase proteins, haptoglobin and serum amyloid A, as serum biomarkers during active sheep scab i
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RESEARCH
VETERINARY RESEARCH
Open Access
Two major ruminant acute phase proteins, haptoglobin and serum amyloid A, as serum biomarkers during active sheep scab infestation Beth Wells1*, Giles T Innocent2, Peter D Eckersall3, Eilidh McCulloch4, Alasdair J Nisbet1 and Stewart TG Burgess1
Abstract Two ruminant acute phase proteins (APPs), haptoglobin (Hp) and serum amyloid A (SAA), were evaluated as serum biomarkers (BMs) for sheep scab–a highly contagious ectoparasitic disease caused by the mite Psoroptes ovis, which is a major welfare and production threat worldwide. The levels of both APPs increased in serum following experimental infestation of sheep with P. ovis, becoming statistically significantly elevated from pre-infestation levels at 4 weeks post-infestation. Following successful treatment of infested sheep with an endectocide, Hp and SAA serum levels declined rapidly, with half lives of less than 3 days. In contrast, serum IgG levels which specifically bound the P. ovis-derived diagnostic antigen Pso o 2 had a half-life of 56 days. Taking into account pre-infestation serum levels, rapidity of response to infestation and test sensitivity at the estimated optimum cut-off values, SAA was the more discriminatory marker. These studies illustrated the potential of SAA and Hp to indicate current sheep scab infestation status and to augment the existing Pso o 2 serological assay to give disease-specific indications of both infestation and successful treatment.
Introduction Sheep scab, caused by the infestation of sheep skin with the highly contagious mite Psoroptes ovis, affects the productivity and welfare of sheep as it produces intensely pruritic lesions and wool loss. These factors, along with the high cost of treatment, mean this disease has significant economic implications for the sheep industries of affected countries [1]. In the UK, the incidence of the disease has increased to a level that it is now endemic [2] with the national annual prevalence estimated at > 7000 outbreaks [3]. This has resulted in the disease being made notifiable in a number of countries (e.g. in Scotland through the Sheep Scab (Scotland) Order 2010 [4]), which has renewed the focus on accurate diagnosis for effective control. Accurate diagnosis can be challenging - clinical signs in P. ovis infested sheep may be minimal during early infestation (up to several months in the field) and easily missed but these animals represent a source of infestation [5]. In such a
* Correspondence: [email protected] 1 Moredun Research Institute, Pentlands Science Park, Midlothian EH26 0PZ, UK Full list of author information is available at the end of the article
situation, mites can be difficult to locate and the sensitivity of the microscopic detection of mites in skin scrapings from these animals can be as low as 18% [6]. In addition to P. ovis, other ectoparasites such as ticks and lice can induce skin reactions which may appear similar to those seen in early infestation with P. ovis [7,8] and dual infestations with more than one ect
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