Experimental infestations of Sarcoptes scabiei (De Geer) were established to study development of cutaneous hypersensitivity in pigs. Forty-eight pigs in six isolation rooms were used in two trials lasting 51 and 65 days, respectively. Treatments of 0 (control), 100 (low dose), and 1000 mites (high dose) per pig were randomly assigned to rooms. Intradermal skin tests with a sterile mite extract were done weekly to assess hypersensitivity. Control pigs never responded to the extract, whereas most infested pigs progressed through phases of (1) no response, (2) delayed hypersensitivity alone, (3) immediate and delayed hypersensitivity together, and (4) immediate hypersensitivity alone. High-dose pigs developed delayed and immediate hypersensiti than low-dose pigs (P<0.05). When related to cumulative mite-days, a measure of exposure to mite antigens, low-dose and high-dose pigs developed delayed responses after experiencing the same level of exposure. Thereafter, immediate responses developed sooner in low-dose pigs, suggesting that immediate hypersensitivity develops at a rate that is independent of rate of antigen exposure.
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Drs. M. Dahl, T. Molitor and D. Ragsdale engaged in helpful discussions while planning this research. We thank V. Cervenka, K. Kjer, D. Moe Nelson, R. Warzynski for help handling pigs; and Drs. D. Ragsdale and B. Stromberg commented on earlier drafts of the manuscript. Contribution No. 17,497 of the Minnesota Agricultural Experiment Station based on research supported by the Station and additional grants from the University of Minnesota Swine Center.
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