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1 November 2009 Inducing Active and Passive Immunity in Sheep to Paralysis Caused by Dermacentor andersoni
T. J. Lysyk, D. M. Veira, J. P. Kastelic, W. Majak
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Arcott sheep were evaluated as a model for studying active and passive immunity to tick paralysis caused by Dermacentor andersoni (Stiles). The incidence of tick paralysis in sheep increased from 0 at doses ≤0.33 ticks per kg to 100% at ≥0.8 ticks per kg. The dose required for 50% paralysis was 0.42 ticks per kg. Expressing dose as a ratio of initial ticks per unit body weight removed differences in response due to sheep weight. The interval from infestation to paralysis decreased from >12 d at 0.4 ticks per kg to <8 d at 1.3 ticks per kg. After exposure to a paralyzing doses of ticks, the incidence of paralysis varied among sheep that were naive (six of six, 100% paralysis), previously paralyzed (zero of six, 0% paralysis), and passively immunized with an intravenous treatment of 300 ml of serum from immune cattle (two of six, 33% paralysis). Sheep that were actively immunized by previous exposure had antibodies to a greater number of tick salivary antigens compared with those that were not immune. Antibodies to a 43.3-kDa antigen had 72% agreement with immunity to paralysis, and a sensitivity and specificity of 0.60 and 0.88, respectively. In conclusion, previously paralyzed sheep had developed antibodies against D. andersoni and were not susceptible to subsequent paralysis, whereas passive immunization conferred protection against paralysis in only some sheep.

T. J. Lysyk, D. M. Veira, J. P. Kastelic, and W. Majak "Inducing Active and Passive Immunity in Sheep to Paralysis Caused by Dermacentor andersoni," Journal of Medical Entomology 46(6), 1436-1441, (1 November 2009).
Received: 1 June 2009; Accepted: 1 August 2009; Published: 1 November 2009

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Dermacentor andersoni
Rocky Mountain wood tick
tick paralysis
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